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1H.“

EFFECTS OF PfiITION AND AWE. UPON
{RBI RECIROCARDIOGRAM OF 'JEE NORMAL DOG

mom moms m

AN ABSTRACT OF

ATEEBIB

Submitted to the College of Science and. Arts,
Division of Biological Science
Michigan State University of Agriculture and
Applied Science in partial fulfillnent of
the requirements for the degree of

ESTER OF SOME

Departmnt of Physiology

1956

 

APPROVED /% (a WM

ABSTRACT

Electrocardiograms from unipolar and bipolar limb leads and
six precordial leads were taken on twenty ”normal" mongrel dogs
anesthetized with 30 mg./kg. body wt. of sodium pentobarbital in
the right side, supine, left side and prone positions. Tracings
were also made on six trained mongrel dogs in the supine position
while unanesthetized, and while anesthetized on two different
occasions.

The amplitudes of the major deflection of the QRS group were
measured for each position and each limb lead, and effects of
position on these leads were compared by Student "t“ tests. Seven
cases of significant change in the ECG due to change of position
were found for these leads. All cases of significant difference
were explainable by assumptions. (1) The heart may rotate in a
clockwise direction (looking from an apex perspective) when the
position changes from right side to prone, and in a counter-clock-
wise direction with a right side to supine positional change.

(2) The heart may also shift from side to side, or up and down
with changes of position. (3) The electrocardiographic result of
a change in position is influenced by both of these cardiac shifts,
but, of course, the particular positional charge will determine
which shift will dominate. Effects of changes in position are not
always predictable, however. Effects of anesthesia, or time-to-

tine variation on the major QR or S deflection were not predict-

able .

Q waves occurred most frequently in lead I with the animal
on its right side, and least frequently in lead I with the ani-
mal on its left side. These observations were confirmed by
simultaneous comparison of leads aVR and aVL, and attributed to
the influence of the former on lead I. It was proposed that,
with a shift from the left to the right side, segments of ear-
liest depolarization (mid-anterior septum and anterior right
ventricle) may shift from the proximal to the distal region of
lead aVR, according to the ”zonal interference” theory of Nahum
and co -workers.

Anesthesia (sodium pentobarbital) suppresses Q waves, as was
indicated by the fact that 65% of the tracings taken on unanes-
thetized dogs (leads I, II, III and a VF) contained Q waves,
whereas only 12$ of those taken on anesthetized dogs did.

Positional effects, and effects of anesthesia on the P an}. T
waves and ST segment were small and not predictable. Depression
of the ST segment was usually accompanied by a deep 8 wave, which
my be due to interference between depolarization and repolariza-
tion potentials in different segments.

Heart rate has a slight influence on the length of the PR and
91' intervals. Host of the variation in heart rate, however, is
”absorbed" by the Te? isoelectric segment .

lembutal in large doses (30 mg./kg. body wt.) causes tachy-
cardia, but in light doses (20 mg./kg.) yields nearly normal heart
rates. 1

Analyses of precordial leads, to detemine QRS and 'f spatial

vectors and transitional pathways, indicated that additional leads

to those previously reported would be desirable. Three leads
in addition to lead V1 were proposed for the right chest, and

one additional lead was proposed for the left chest.

EFFECTS OF PCBITION AND AWE UPON
THE HECTROCARDICBRAM OF HE NORMAL Dd}

BY

IEONARD THOMS BLOUI]

ATEISIS

Submitted to the College of Science and Arts,
Division of Biological Science
Michigan State University of Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

m 01‘ SCIENCE

Department of Physiology

1956

ACKNOWLEDGEMENTS

The author wishes to acknowledge Dr» H} D. Collings, Professor,
of the Department of’Physiology, Michigan State University, for
his aid in selecting the project and invaluable assistance and
counsel during its pursual; R. G. Schirmer, Associate Professor,
of the Department of’Surgery and Medicine, Michigan.State‘Uni-
versity for his encouragement at the beginning; Dr. W. D. Baten,
of the Agricultural Experiment Station, Michigan State Univer-
sity, and Dr. G. B. Spurr of the Institute of Clinical Investi-
gation, Department of Physiology, University of Tennessee,

for their assistance in the statistal treatment; Dr. R. R.
Overman, Professor of Clinical.Physiology,‘University of
Tennessee, for making facilities available for reproduction

of the figures; and.my wife, Beverly, for her patience and

assistance during the course of the project.

TO

MY

WIFE

TABIE OF CONTENTS

Introduction ................. .. 1
Historical Survey ............... 3
Procedure and Materials ............ 15
Results--------------.. ..... 21
Discussion and Conclusions .. - ......... hl
Summary --------------- - - - - - 59

TABLE 1.

TABIE 2.

TABLE 3.

TABLE 14.

TABIE5.

TABLE6.

LISTOFTABIIB

Major Q, R or S Deflections - - - - - 22

“t" Values for Comparison of
Positional Effects on Q, R or
S Deflections ....... .. - - .. - his

Frequency of Occurrence of Q
orSVaves-.. ----- ...... 28

Amplitude and Direction of P
and T Waves and ST Segment ..... 32

Location of the Transitional
PathwayforQRSandT -- - .. - .. .. 37

PR, QIB and QT Intervals;
Heart Rates - - - - .. ....... 39

FIG .

FIG .

FIG 0

FIG 0

FIG .

FIG.

FIG.

FIG.

1.

9.

LIST OF FIGURES

Revolving Dog Board and Stand .....

Needle Electrode ....... - - - -

Precordial Switch ...........

Precordial Electrode Placement - - - -

Types of Unipolar Tracings .. - .. ..

Spatial QBS and T Vectors ...... -

TVectors - DogC ---- .....

The Dog Heart - .. .. - .‘ ........

Examples or Classification by Rank

16

16

16

18

35

143

51

INTRODUCT ION

Though the dog is frequently used in experimental electrocardio-
graphic (ECG) studies, extensive and systematic data concerned with
the normal dog picture has been lacking. Many authors have nade
recordings on normal dogs, but the work has not, on the whole, en-
riched our knowledge of such factors as body position or the in-
fluence of anesthetics on the normal record. One recent publica-
tion made a systematic approach to the effects of position on the
ECG, but only bipolar limb leads and unipolar chest leads were em-
ployed.

Unipolar limb lead data have been meager, and no positional
studies have been found which employed these important leads.
Goldberger points out several reasons why unipolar limb lead data
are more useful than bipolar data. To name a few: The spread of
a stimulus through the heart can be correlated with the pattern of
a unipolar lead; a positive potential is always recorded by an up-
ward deflection in a unipolar lead; the effect of changes in posi-
tion of the heart on the electrocardiogram can be easily demon-
strated; several clinical conditions can be best diagnosed by uni-
polar pattems.

Except in a few cases, placement of electrodes in ECG studies
on dogs has lacked any standardization. Several authors have
patterned chest lead positions closely after analogous placement
on the human subject. Considering the marked difference in elec-
trocardiographic position of the heart that has been reported be-

tween the humn subject and the dog, perhaps a modification of

such placement on the latter is in order. In dogs, the plane
which is defined by the transitional pathway of the spatial vec-
tor is probably markedly different from that in humans.

The primary intent of the present work is to provide unipolar
lhnb lead data and interpretation of these as related to body
position, and anesthetized compared to trained dogs. .Additional
data concerning the influence of these variables on the standard
lflmb leads and precordial leads are presented. In addition,
some investigations on placement of precordial.electrodes are

discussed.

HISTORICAL SURVEY

General.

According to Lannek (l2), Norr, in 1922, was one of the first
to use a clinical approachto the dog ECG. He employed glass tanks
filled with saline, or bandages soaked in zinc sulfate, as limb
electrodes. The prone or side position was used, but the latter
was found "unsuitable” due to "abnormal position” of the heart.

Eaupt, in 1929, (as reported by Lannek) found the needle elec-
trodes, which had been proposed by Lautenschlager, to be "most
suitable”.

Katz, Soskin and Frisch (9), in 1931+, used saline soaked band-
ages with a copper spiral wrapped around them for electrodes.
They obtained records on three normal dogs twice a week for four
months, using standard bipolar extremity leads. They found ir-
regular fluctuations in the records of the same dog on different
days, and attributed these to variations in position of the dog's
heart at different times, since it was found to be ”relatively
much more mobile than the humn heart”.

Mainzer and Krause (17), in 1937, examined tracings taken on
eight normal dogs in the right side and left side, sitting and
standing positions. They reported that the record obtained in
the standing position was ”useless” due to mscls tremor arti-
facts. In the sitting position, the tracing was said to be most
reproducible, approaching that of reclining man. The ECG taken
in the right or left side position showed mrked day to day vari-

ation which the authors attributed to different degrees of

rigidity of the mediastinum.

Gyarmti, in 1939, (according to Lannek), using standard limb
leads, emphasized that different Ems were obtained with the body
in different positions.

Lalich, Cohen and walker (10), in 191+l, trained a group of
dogs to lie quietly on either side. A series of records, rang-
ing from two to seventeen, were taken on each dog over a period
of four weeks. No consistent correlation between ECG variations
and the side the animal was lying on could be established. The
electrical axis in over sixty per cent of the records was found
by these authors to lie between 50° and 75°, with a usual day to
day shift of less than 15°.

Wilson and co-workers (2%), in 19%, described inspection
methods for determining the electrocardiographic position of the
human heart, which were later applied to the position of the dog
heart by Petersen, et al. (22). Six possible positions were
listed, viz., vertical, semi-vertical, intermediate, semi-hori-
zontal, horizontal and indeterminate. The method was based on
comparison of the ventricular complexes of the unipolar extremity
leads to those of the unipolar chest leads. The ”indeterminate”
position was included to encompass all cases where no obvious re-
lationships existed.

lahum, Chernoff and Kaufman (20), in 191+8, pointed out the re-
lationships that exist between the unipolar am the bipolar ex-
tremity leads. The complexity of possible reasons for certain

configurations in the latter was clearly pointed out. On the

Other hand, they indicate that much more specific information
about certain configurations of the ECG is obtainable from.uni-
polar lead data. Goldberger (2), supports this argument with
several important reasons why unipolar leads are more useful
than bipolar leads.

Lannek (12), in l9h9, conducted.an extensive investigation
into influence of sex, age, respiration, day to day variation
and breed upon certain characteristics of the bipolar'limb and
chest leads. He used stainless steel needles for electrodes,
inserted approximately five millimeters subcutaneously. It was
noted, however, that no difference in the ECG was observable
even when the electrodes were allowed to barely pierce the skin,
as long as the stratum corneum was penetrated.

Petersen and coeworkers (22), in 1951, described fifty trac-
ings taken on thirty-two normal young beagles, ranging in age
from five to twenty-eight months, and ranging in weight from.six
to twelve and a half kilograms. The dogs were placed in the su-
pine position, since the "lateral positions cause variability of
results”. They were untrained.and unanesthetized, and were strap-
ped down to a trough-shaped table. The electrocardiographic
position of the heard (according to‘Hilson's method), was found
to be either vertical or semivertical in all cases. It was fur-
ther noted that variations were small enough in serial tracings
taken in the supine position to render these ”useful".

Grollman and coeworkers (h), in 1952, trained dogs to submit
to restraint in the supine position and took leads I, II, III,

avn, aVL, and aVF and unipolar chest leads as described by the

American Medical Association for man. Curved needles, inserted
subcutaneously, were used for electrodes.

Lombard and Uitham (l5) , in 1955, anesthetized dogs with mor-
phine and sodium pento'barbital to obtain ECGs. Straight needle
electrodes were used. Electrode placement differed somewhat from
the human scheme in that a V ”anterior” (Va) electrode was placed
midway between V1 and Y2, directly over the sternum.

The authors reported that changes in position affect the ECG
in a random way with the exception of Q waves and ST segments,
”which precludes any possibility of being able to predict whether
or not such variations will occur“. They recommended that all
recordings be taken in the same position at all times throughout a
given experiment.

Order of Cardiac Excitation.

 

Harris (6), in l9hl, described the order of excitation of the
ventricles of the dog. He reported that the points of earliest
excitation were "the central area of the right ventricle and the
nearjmid septum“. The impulse arrives at other ventricular areas
later, and latest at the pulmonary conus. It arrives at all parts
of the endocardium almost simultaneously, but proceeds through the
uocardium to the surface much more slowly, according to this
author.

Nahum, Chernoff and Kaufman (18), in 1919 , pointed out that the
ventricular complexes of the unipolar limb leads tend to resemble
each other closely, and that when simultaneously recorded in these

three leads, could be readily analyzed to determine the spread of

excitation in the dog ventricle. ”Analysis of the deflection
positions of the QRS group in each lead from moment to moment
allows determination of the time when depolarization occurs in
the various segments.” They reported that the usual order of
excitation was: mid-anterior septum-- anterior right ventricle--
posterior right ventricle-- left apex and posterior left ventri-
cle-- pulmonary conus.

These same authors (19), in l9h8, proposed a ”zonal interfer-
ence” theory to explain the electrocardiographic configurations
observed in the unipolar limb leads. ‘Using a technique of ”ex-
tra—systoles' (artifically elicited by stimulation of various
points on the surface of the heart), they found that a "proximal"
zone and a ”distal” zone could be determined for each lead. Be-
tween these zones, a net isoelectric ”intermediate” zone of vary-
ing width was mapped for each 16364 .According to the authors,
when depolarization occurs in the “proximal” zone of a given lead,
a downward deflection occurs; when in the distal zone, an upward
deflection results; and when in the intermediate zone, either no
deflection, or a not zero transitional wave occurs. These deflec-
tions were stated to be independent of tin pathway by which the
excitation arrives. IDepolarization in both "active” zones at the
same time causes a deflection which depends on the irrelative
”strengths” with respect to a given lead, or depends on "interfer-
ence'I between the two depolarizations. The authors ascribed an
upright “T” wave to repolarization progressing more slowly in the
”distal" segments than in the ”proximal” segments; whereas invert-

ed "T" waves indicate the opposite condition.

7

Nahum and Hoff (21) , in 195.9, in describing the precordial
soc, stated that the precordial leads differ from unipolar limb
leads only in that the areas involved in the ”interference” are
unequal in size and differently located. They stated further
that it is a matter of indifference whether the endocardial or
epicardial surface of the mocardium is first to be excited.

Heart Rates.

 

Heart rates in unanesthetized dogs have been reported to range
from 62 to 2113 cycles per minute during the taking of EOGs the
higher rates being attributed to an excited state, or to certain
breed differences. The predominant rhythm, typically, was re-
ported to be sinus arrhythmia (5, 8, 12, 16, 22).

Lalich, Walker and Cohen (11), in l9hl, found that sodium
pentobarbital in anesthetic doses causes tachycardia.

Amplitudes and Intervals .

 

Harris and Hussey (7), in 1936, reported extreme variability
in the normal ECG of the dog. They conducted a study with fifty
dogs. TI was found positive in thirteen, isoelectric in ten,
diphasic in two and inverted in twenty -five . Of the twenty-five
deg: with inverted TI waves, TH was positive in six, diphasic in
nine and negative in ten, and TIII was positive in fifteen diphasic
in four and negative in six, indicating random variations in TH)
and nondependable relationships in TI and TIII‘ The authors em-
phasized that the interpretation of the tracing after coronary
closure is of no great value unless it is studied in comparison

with a control tracing, which served to reinforce the concept that

more normal data were needed on the dog. However, in the analy-
sis of ST segments, much less variability was noted. Only one
case of ST segment deviation was found.

Betlach (l), in 1937, studied day to day variations in one
animal. Sixty-three tracings were taken over a three month
period. He reported that fifty-two per cent of the records had
a negative T wave in leads I, II and III; forty per cent had a
negative T in leads I and II, but diphasic T in lead III; and
eight per cent had a negative TI, a diphasic TII and positive
TIII‘

He also observed that other caused negative T waves to become
positive in all three bipolar leads; cyclopropane had the same
effect in leads II and III; and sodium amytal and sodium pento-
thal caused no significant changes in any of the leads. In the
anesthetic studies, four dogs were used which had been trained to
lie on their right sides for control tracings.

Lepeschkin (13), in 1938, noted that a relationship between

the QT interval and the heart rate (R-R interval) existed, where-

by: QTIF \quR

where F a 6, 7.95 or 8.25 as reported by various authors.

Lalich EP- 31. (11), in l9hl, noted that sodium pentobarbital
produces tachycardia, may produce ST segment deviation and may
cause inversion of positive T waves. In the normal dog, they ob-
served that inverted or diphasic (+ —+) T waves are most common.

The same authors (10), in l9hl, studied serial tracings taken

on normal dogs over a four week period on the left or right side.

They reported P amplitude variation associated with sinus arrhyth-
sis in sixteen cases in lead II and twelve cases in lead III. P
wave inversion was observed in leads I and III, but never in lead
II. They noted further that when a Q wave occurred in lead I,
the T wave was frequently inverted. It was stressed that when
the amplitude of Q exceeded 1+ m. the following T wave was invert-
ed in ninety per cent of the cases in all three leads. Q waves
were deepest and most frequent in lead II. whenever T shifted
from inverted to upright, Q became small or disappeared. NS waves
were present most frequently in lead III. It was noted that when-
ever an S wave occurred, an upright T wave was usually found in
any lead especially lead III. Upright T waves in lead III, and
inverted T waves in lead Iwere common, and a reciprocal relation-
ship was often found. The authors also noted that Q and S were
found together most frequently in lead III and least frequently
in lead I. then they occurred together in either lead, one of
the waves was usually very small. In lead II, however, when Q
and S occurred together, both often exceeded 2 n. in amplitude.
Luisada, Heise and Hantmn (16), in 19%, used dogs of three
sizes in a study of the ECG. A snall dachshund, middle sized
mongrel and a large dane were selected. They reported respira-
tory arrhythmia in all three dogs, especially the dachshund.
Sharp, upright P waves were observed in all cases. The T waves
were usually diphasic, and the ST segment was often misplaced.
The intervals, measured in seconds, were: PR 2 0.10 to 0.13,

gas : 0.07 to 0.08 and QT = 0.20 to men.

10

Hafkesbring and Hertenberger (5), in 191+? , used mongrel fe-
male dogs averaging eight kilograms in weight. Serial tracings
were taken on each dog. line cases of ST segment deviation were
noted. The T waves were found variable. Intervals reported were:
ER : 0.091 to 0.13% seconds, and.QRS = 0.026 to 0.059 seconds.

Lannek (12), in 19h9, reported findings of a rather extensive
investigation using pure.bred dogs. IHe noted that PI was often
isoelectric, PII and?III were positive on inspiration, but PIII
sometimes became negative during expiration. It was stated that
R wave amplitudes, while usually not of great diagnostic value in
themselves, became important when abnormally small, and on calcu-
lation of the negative T wave as a percentage of the‘R amplitude.
T waves were reported diphasic in six, thirty—two and twenty-four
per>cent of the cases in leads I, II and III, respectively. In
all leads a regular (—+) pattern was observed. Shifting of the
ST segment toward the negative was felt to be, clinically, the
:Iost significant feature. The authors related.QT and the heart
rate by the fonlula:

qr : 16 i: .03(R-R) :l: 3.8
'where the interval was expressed in hundredths of a second, and
3.8 indicates limits of - 2! the standard error.

The Q18 axis was reported to be of little clinical importance,
and normal variation was found to be wide. The mean axis was cal-
culated to be 79° and a standard deviation of t2h.6° was determined.

With respect to nor-ally encountered variables, large differ-

ences in the tracings were found between different breeds of dogs,

11

small differences due to age were reported in mature dogs, and
little or no difference between sexes could be ascertained.

Petersen, gt_al. (22), in 1951, analyzing fifty tracings taken
on beagles, observed that two patterns were normally encountered
in the ventricular portion of the ECG, viz., a large group in
which a small or no 8 wave was present in aVF associated with a
QS pattern and inverted.T waves in avR and aVL; and a smaller
group in which a prominent S wave in aVF was associated with a
QB.pattern in.aYR and avL. The T wave was usually isoelectric
in lead I; always upright in leads II, III and an and usually
inverted in leads aVR and.aYL, according to the authors. It was
also observed that positive T waves never became negative in leads
II, III and.aVF on serial tracings taken on the same dog. Inter-
vals and amplitudes for the ”mean beagle dog” were also reported
by the authors. '

Grollman, 33'. _a_l_. (h), in 1952, observed that the QRS complex
was small and.T wave frequently inverted in lead I, whereas the
R wave was large and.T upright in leads II, III and.aflr. Large
QB deflections and isoelectric'T waves were observed in ave and
aNL. It was stated that, using precordial leads, moderate R
waves, small 8 waves, (or almost equal R and S waves), and posi-
tive T waves were found in leads'V1_3. 'Large R waves, small 8
waves were reported for'Vh_5. The authors reported interval
ranges of; PR = 0.06 to 0.18 and.QRS 2 0.03 to 0.08 seconds.
The large variability was probably related to the condition of

”restraint in the supine position”.

12

Lepeschkin (11+), in 1951 , quoted FuJiwara concerning a rela-

tionship between the PR interval and heart rate in dogs, viz.
PR 8 6.h2 (113)0'122

Hoffman and Suckling (8), in 19515 studied the effect of heart
rate upon the unipolar electrogram of a papillary muscle fiber.
Using an intracellular microelectrode, they found that the T wave
varies directly in magnitude with the rate of repolarization of
the membrane as reported by many earlier authors, and is not pro-
duced by after-potentials or oxidative recovery processes. This
adds new support to the old theory that the T wave represents re-
polarization of the membrane. The authors noted further that the
only significant change in configuration of the ECG produced by
large variations in heart rate was in the duration of the QT inter-
val where a linear relationship was demonstrated by single fiber
recordings.

Lombard and Witham (15), observed that the T wave was most vari-
able in dogs anesthetized with morphine and sodium pentobarbital.
With changes in position, the only significant difference in the
ST segnent was found between tracings taken with the dog on the
left side and belly in leads III and V6; the right side and belly
in lead V5; and the back and left side in lead V6. A contour
method was described for classification of leads I, II, III and
the unipolar chest leads. The authors reported that they were
unable to confirm the idea of Lalich and co-workers, that a rela-
tion existed between the presence of Q waves and tlm direction

of T waves.

13

The longest PR, QRS and QT intervals found in any of the leads
were reported, viz.’PR = 0.08 to 0.15, was : 0.01 to 0.06 and
QT : 0.20 to 0.38.

A large variability was found in the QRS axes of the fifty

dogs, from -123° to +151".

1h

PROCEJIJRE AND MTERIAIS

Positional Dogs .

 

Twenty mongrel dogs of both sexes, ranging in weight from 7.5
to 18 kilograms were used to study effects of position on the
ECG. All dogs were anesthetized with 30 mg./kg. body wt. of
sodium pentobarbital.

A revolving dog board and stand was designed, which permitted
a rapid and reproducible change of position witholt interference
with electrodes. The dog was placed in the supine position on
a trough-shaped board, and the animal's legs were fixed in posi-
tion by padded ropes. A retaining cloth was then tied in posi-
tion around the thighs, abdomen, chest and neck such that when
the dog was turned to the side or prone positions, it was held
in a firm but gentle manner. By this means, pressure upon the
diaphragm was minimized, to avoid influence on the ECG. The
board was provided with a pin which locked it in 90° positions,
(supine, right side, prone and left side) (Fig. l).

Electrodes and Placement.

 

Hypodermic needles (#22) were bent into a hook shape such
that approximately one centimeter could be inserted subcutaneous-
1y. By application of a slight pressure on the lead wire, these
electrodes remained in place even while the dog was being ro-
tated. Banana plugs were used to connect the needles to stand-
ard BOG cable tips. A one-eighth inch diameter center hole was

bored in the plugs, which allowed a snug fit over the cable tips

15

rslsinlnq cloth ‘

encheflsq vase

lacuna
pm

  
  

 

 

 

 

FIG. i.

Revolving doq

e—i (Position) 2 ——,

tang:

 

 

 

\ \

H6 3

Precordiol

switch

 

board

 

 

 

 

and Hand.
"""" '1
1
L - -..- _--J
bosons slug

3

 

 

0000's!

 

FIG. 2. Noodle

electrode

 

(Fig. 2). Limb electrodes were inserted on the lateral side
about 3-5 cm. above the knee Joint in the ”fleshy" part of each
leg. Chest electrodes were placed as described in Fig. h. For
all of the positional studies and most of the trained deg studies,
six chest positions were employed, viz. , VI, Va, V2, V1,, V5 and
V6. These were patterned after the standard human chest elec-
trode placement. The extra (Va) position corresponds to the
”sternum” position used by Lombard and witham (15). The addi-
tional positions VB, V9, V10, V12, 713 and VIII» were employed to
study further the adequacy of “standard" placement with respect
to Q83 and T spatial vectors. This study will be discussed later.

ECG Instrument and Precordial Switch.

 

A h-channel Sanborn (Model 67) direct writing electrocardio-
graph was used for the studies. Remarkable stability was noted,
and very little difficulty with artifacts was encountered. A
hPDI‘ non-shorting switch (Fig. 3) was equipped with a box contain.-
ing female phone plug adapters, into which the standard chest
cable tips could be inserted. Shielded leads from the switch
were attached to banana plugs for connection with the precordial
electrodes. In this mnner, the six chest leads could be traced,
three at a time, with a simple flip of the switch, rather than
dis -connecting the plugs from the electrodes each time. The
chest leads were connected to channels B, C and D, which left
channel A open for heart sounds or any other desired tracing.

(In this study leads CR1“ cm, and 0L1, were traced in channel A

with the switch in position 1, and supplementary tracings

17

 

 

 

 

'\
--‘-¢‘---
\
'0.
\

@©@

as
One

1:; l4 (done! side)

 

 

 

 

FIG. 4. Precordiol Electrode Placement.

 

H

E?

 

FSKSwmmu F'I'OD H

 

Numbers refer—to V lead subscripts, as in the text.

KBITION GP memos:

Junction of B. hth intercostal space and sternum
Midway between 1 and 2, on the sternum

Junction of L. hth intercostal space and sternum

5th interoostal space, 1/3 distance between 2 and 6
Hidway between it and 6

L. lid-axillary line, on horizontal line with Ii» and 5
R. mid-axillary line, on horizontal line with 9 and 10
Midway between 8 and 10

3rd intercostal space, 1 cm. to R. of R. nipple line
7th Intercostal space, on a diagonal line with a and 1i
9th intercostal space, on a diagonal line with a, h and 12
11th intercostal space, 1/3 distance between L. mid-
axillary line and mid-dorsal line.

18

(sounds, etc.) could be introduced directly into channel A when
the switch was in position 2 (open). No artifacts were encount-
ered due to the switch.

Trained Dogs .

 

Six mongrel dogs were trained to lie quietly in the supine
position for extended periods. Tracings were made on the dogs,
which were then immediately anesthetized and the same tracings
repeated. Twenty mg./kg. body wt. of sodium pentobarbital was
used for the group, since a preliminary study indicated that
approximately normal heart rates were obtained at this level.
The dogs were completely unconscious at this stage, but still
had a positive paw-pinch reflex. Comparison of the two sets of
tracings would allow some generalizations to be made concerning
effects of light anesthesia. The two sets were taken as close
together as possible, as noted above, to avoid or minimize time-
to-time variation. Three of these dogs (A, B and C) were further
trained to lie quietly in all four positions, and tracings were
mde.

Day -to allay Variati on .

 

The same six dogs were used to study day-to—day changes in the
ECG. They were again anesthetized with 20 mg./kg. sodium pento-
barbital after an interval of two to five days following the first
run anesthetized. The study was designated (Anesthetized-aid Run).

Respiratory Influence .

 

Approximately fifteen cardiac cycles were recorded at each

tracing, which covered an interval of one or two respiratory

19

cycles. Data were then taken from the recording at random, but
including highs and lows. In this manner, respiratory effects
were minimized.

Measurements .

 

The major deflection of the QBS group was measured in milli-
meters of amplitude from the top or bottom of the isoelectric
T - P segment to the peak of the wave. Upright waves were called
positive and inverted waves were preceded by a negative sign.

The PR interval, QRS interval and QT interval were measured
in seconds of duration by relating the paper speed (50 al./sec.)
to the linear distance measured for each interval. The PR inter-
val is measured from the beginning of the P wave to the beginning
of the QRS complex. The QIB interval is measured from the begin-
ning to the end of the QB cmplex. The QT wave is measured from
the beginning of the Q18 complex to the end of the T wave. The
Q16 canplex may start with a negative (Q) or positive (R) deflec-

tion, and terminate with a positive (R) or negative (3) deflection.

RESULTS

Q, R or 8 Amplitude.

 

The amplitude of the mJor ventricular depolarization deflec-
tion (whether Q, R, or S) was measured for each position for tre
bipolar and unipolar limb leads, from the positional tracings
(Table 1). For the trained dogs, Q, R, or S amplitudes were de-
termined for the same leads in the supine position with the ani-
mals unanesthetized or anesthetized (Table lb). Each datum of
tables 1 and lb represents the mean of five random measurements
taken over one or two respiratory cycles. The major deflection
of the QRS complex represents the spread of excitation through
the main portion, or a large segment or segments of tie right and
left ventricles. It is positive (upright, i.e. R or R') when the
segmeut(s) is (are) ”distal” to the lead which is tracing the
phenomenon. 0n the other hand, the deflection is negative (in-
verted, i.e. Q or 8) when the segment(s) is (are) ”proximal” to
the lead tracing it. For this reason, it was measured in the hepe
that it would serve as a useful index of the influence of various
positions of the animal by reflecting shifts of the heart.
"Types" of Uniylar Precordial and Extremity EGs.

ECGs were classified according to "type” by methods similar to
those of Lombard and Hitham. These authors stated that if wide
variations in the magnitude of tin T wave, are. occasional large
84' segment deviations-are recognized as co-on occurrences in
the dog electrocardiogram, the bipolar limb leads could be classi-

fied into four types based on the contour of the QRS complex.

21

mm 1. Major Q, R, or s Deflection (mean), in Millimeters.
Positional Dogs.

 

 

 

 

 

 

 

LEAD POSITION DOG6 D007 13008 DOG9 D0010 1300,11
R 7.6 5.7 5.3 8.6 9.0 12.3
I P 8.2 3.8 5.2 7.11 11.1 10.2
L 5.1 2.8 3.2 6.7 8.1+ 9.5
s 5.7 2.5 5.6 6.3 5.2 9.2
R 26.1 21+.2 12.5 30.1 27.3 20.6
H P 27.0 23.3 13.3 30.8 28.1 17.8
L 25!; 21.6 12.8 30.0 29.1; 18.5
s 25.0 21.6 11+.0 27.8 27.0 21.11
R 19.0 18.9 6.9 21+.3 17.0 8.0
III P 19.6 19.14 7.2 25.h 16.8 8.2
L 20.3 19.h 6.9 2h.h 20.6 9.7
s 19.8 20.0 7.7 21.9 21.3 12.5
i R -17.5 -15.0 __ -19.3 -18.2 -16.0
aVR P -18.1 -13.9 -9.5 -19.8 -18.8 -11+.0
L -16.6 712.1; .8.9 -18.5 -18.5 -12.2
s 16.1 -12.3 -9.8 -17.1 -16.6 411.9
R .7.7 .8.5 -11.3 .h.6 -2.2
an P .8.0 .8.3 -10.8 -5.2 -1.1
L .7.2 .8.3 .9.9 .6.6 -2.3
s .7.3 .8.6 .8.1 .7.6 41.0
R 21.0 20.0 --- 25.3 20.6 13.2
P 22.2 20.0 8.1+ 26.0 22.0 11.8

e.VF
L 21.8 19.0 7.9 25.1 23.0 12.0
s 21.0 18.7 8.5 22.8 22.9 1h.9

22

TABLE 1.

(Continued)

 

 

 

 

 

 

 

LEAD POSITION DOG 12 Doc 13 D00r 1h Doc- 15 DOG 16 DOG 17
R 8.2 6.1 6.h 5.0 h.6 3.9
I P 7.8 5.5 7.7 h.8 3.9 3.6
L 7.0 h.h 8.5 h.2 5.3 3.8
s 6.9 3.9 h.6 h.1 3.8 3.2
n 18.6 19.7 19.8 2h.8 15.0 17.h
II P 18.5 20.2 16.9 25.1 15.6 20.1
L 17.9 20.3 15.7 23.8 17.8 22.0
s 19.0 19.1 19.7 2h.2 16.9 20.5
R 9.9 13.2 1h.5 26.6 10.9 18.1
III P 10.3 13.8 11.3 20.8 12.1 20.5
L 10.1 15.h 7.6 20.2 11.8 19.1
s 12.1 15.1 15.0 21.7 12.2 18.8
R -13.6 -13.0 -12.2 -13.0 .8.6 .9.6
P -12.8 -12.9 -11.9 -13.9 47.8 -9.3
“R L -12.8 -12.8 42.1; 43.5 40.1 41.1.
s -13.0 -11.8 ---- -13.9 .8.5 -11.2
R 4.7 .5.8 .6.0 .7.5 4.6 -9.1
an P -308 th -3e6 .7e7 -109 .8e0
L -3e2 .505 -105 .706 Ill-e9 .801
s .h.5 .5.2 --- 47.5 -h.2 .8.h
R 1h.3 15.2 15.7 19.h 10.7 15.8
avr P 12.7 15.5 13.0 20.7 9.7 17.1
L 12.5 16.7 10.6 20.h 10.7 18.5'
s 1h.1 --- 20.2 11.9 17.0

15.6

23

TABLE 1. (Continued)

 

 

 

 

 

 

 

LEADPCB'N D0018 D0019 D0020 D0021 D0022 D0023 DOG21+
R 3.8 11.5 1.7 6.5 8.6 5.9 11.3
I P 3.h h.5 1.7 6.0 7.5 6.8 11.1
L 11.3 11.6 1.8 11.1». 6.2 7.3 3.8
s 3.9 3.9 1.0 0.7 5.8 5.h 3.8
R 11.1 15.5 13.8 16.5 23.7 10.9 12.1
II P 12.1 16.h 16.1 15.1 22.9 12.8 13.2
L 12.9 11.8 16.6 13.5 23.h 11.1; 13.6
s 13.0 15.6 1h.7 13.8 ' 23.7 12.8 13.11
R 6.5 11.0 12.0 10.2 15.5 .7.9 7.5
In P 8.0 17.7 111.8 9.2 15.5 .7.7 8.5
L 8.1+ 12.9 111.9 9.0 17.7 -9.5 8.6
s 8.8 12.3 1h.0 9.1 18.5 9°&9.1 9.1
R .9.5 .9.5 .7.1 .6.7 46.11 .8.2 .7.9
aVR P .911 .9.6 .8.8 .5.5 -15.7 .841 .8.3
L .8.8 -10.0 .8.8 --.... 411.6 .8.7 .8.1
s .8.8 -9.5 .7.0 ---- -15.9 .7.6 .7.9
R 4.0 -5.h -5.5 11.1 -5.2- 5.1 -2.5
an P -3.8 41.5 -5.6 3.2 -2.9 h.1 -2.5
L J+.5 -5.7 6.». ---- .6.2 5.1 -3.2
s .14 -5.3 .6.1 an -5.1 5.5 -2.7
R 9.0 12.3 12.5 9.0 18.2 8.3 9.1
”F P 10.2 12.2 1h.1 7.6 16.5 6.7 9.1
L 10.7 13.8 111.3 mm 18.0 5.2 10.5
s 10.5 13.0 12.5 ---- 19.h 9.1 9.7

21+

 

 

 

 

 

 

 

 

 

 

 

 

TABLE lb. Major Q, R, or S deflection; Trained Dogs; Supine
Position.
D00

IEAD RUN# ATE 3m CTR DTR Em FTR
Unanesthetized 10.5 3.9 17.2 7.3 5.0 8.1
I Anesth. 1st 10.1 3.7 16.0 7.2 2.0 7.5
Anesth. 2nd 11.3 3.7 9.0 6.8 2.9 7.7
Unan. 20.h 11.2 22.1 21.0 11.8 30.1
II Anesth. 18+. 20.9 10.9 23.8 22.1 10.3 30.0
Anesth. 2nd 19.6 9.6 20.5 22.1 10.3 29.3
Unan. 11.3 5.8 3.9 13.9 5.0 19.6
III Anesth. lst 12.1 5.9 7.0 15.7 7.8 20.0
Anesth. 2nd 9.7 6.0 8.6 111.1 8.0 20.6
Unan. 45.7 .6.1 -19.6 -Ih.1 .7.5 -19.1
aVR Anesth. let 411.7 -6.8 ~17.3 -l.5.l ~5.1 418.5
Anesth. 2nd 45.6 -6.1 -12.? -13.6 -6.7 -18.5
Unan. -2.8 2.6 AA 7.0 1.8 11.3
aVI. Anesth. lst -3.9 3.2 3.2 kit 2.”. 5.8
Anesth. 2nd -2.5 3.2 3.1 5.2 1.8 7.5
Unan. 111.9 7.6 12.6 19.9 8.1 21.11
aVF Anesth. lst 15.1 7.h 13.8 17.5 8.11 23.0
Anesth. 2nd 12.9 6.9 12.9 16.0 9.2 23.1

Following this line of reasoning, the unipolar limb leads of the
present study were classified into four types according to the
contour of the QRS complex of leads 3 YR, aVL am am, when trese
were simultaneously compared.(Fig. 5). The types were labeled
according to the direction of the initial, intermediate, and final
deflections of the QRS complex. For example, type RSR'aVL indi-
cates an initial upward deflection, followed by an intermediate
downward deflection, and a final upward deflection, in lead aVL.
In the other cases, an initial downward deflection was always called
Q” a downward deflection following the first upward.deflection was
called S, and all upward deflections were called.R, (or if two up-
ward deflections were present, the second'was called R').

The precordial leads were classified into three types accord-
ing to the location of the transitional pathway. For example, V1
and/or'va indicates that high.R waves appeared in leads to the
left of'Va, but diphasic waves, with equal areas in the upward
and downward components, appeared in leads‘vl or‘Va or both.

Q and S Haves.

The frequencies of occurrence of Q and S waves one millimeter
or more deep were tabulated for the unipolar and bipolar extreme
ity leads (Table 3). Lalich (10) reported a relationship between
0 and T waves, and Lombard and Hitham (15) indicated an influence
of position on the frequency and magnitude of Q waves. It was de-
sired to confirm these findings, if possible, and to show any
similar relationships or influence on the 8 wave, or interrela-

tionships of these two negative deflections of the Q18 complex.

26

 

 

 

 

 

 

 

 

TYPE 3': sVR oVL sVF
RSR;VR A

and 60 “N
ORsoVF v
QRoVL

and 20 W5 A LV-
RsoVF
0R

OVR

and 5 ‘4? %
QRsoVF U
Rss'avR A

and I5 ' Ii—‘F-\fl-
RsoVF

 

 

 

 

 

(a) Unipolar Limb Leeds

 

 

 

 

 

 

 

 

 

 

 

TYPE 31'.“ 0 2 4 5 e
'V. 764" J)" J" ‘L‘L‘L
Mona/.rvawm ’4’» ’A‘ »L\ aAa~ «J...

 

 

(b) Precerdiel Leeds

FIG. 5.

Types

 

Tracings.

 

 

 

TABLE 3.

Frequency of Occurrence of Q or S Waves at Least One mm. Deep.

 

 

IEAD II III
POSITION R P S R P L S R P L S
DOG NUMBER

5 Q Q Q q8 8 (18 q s s s s
6 Q q q qS qS S qS S S qS qS
7 q - - S S S S S S S S
8 s s s S S S S s s S S
9 Q <1 <1 8 s s s s s s s

10 - - - S S S S S S S qS

ll - - - s s s s s qs qs qs

12 Q <1 - qs qs s s s s s s

13 Q <1 - <18 <18 <18 <18 <18 <18 <18 <18

11!- Q q q qS qS S qS S S qs S

15 - - - s s S s S S S S

16 q - 3 QB s s s s s s s

17 q q - qs qs s qs s s s qs

18 q - - s s s s s s s s

19 <1 q - <19 3 S s S S S S

20 s s S S S S S S S S

21 q* q* q -* J S qs s* s* S S

22 Q - - Qs qs s qs qs qs qs qS

23 q - - S S S S S S S S

211 q - - qS qS qS qS S S S qS

28

(Continued)

TABLE 3.

 

LEAD

P

R

RBITION

 

DWNUMBER

(18

Q Q. Q Q

Q.

S—

8—

S qS

qS

Q. Q Q. Q

Q

S—

S.

S.

Q. Q. Q. Q. Q

7

Q. Q. Q. ‘Q

Q.

Q
Q. Q. Q. Q

.S.

S

Q. Q. Q. Q

10

S.

a:

Q. -Q. Q. Q. q

11

qs qs qs qs

Q Q. Q Q

?

qs qs

S.

S.

Q. Q. Q. 'Q

Q. Q. Q Q

15
16

S.

S—

S.

S.

qs (138

Q. Q. Q. 'Q

17
18

Q. Q. Q. Q

Q

Q.

Q.
Q. Q. Q. ‘Q
0* q* death

QQQQ <18

Q.

S.

S—

19

S

Q. Q. Q. Q
q* q* death

20

8* 8* death

21

S.

S—

S.

22

qs qs qs qs

S
qs qs qs qS

as Q».

S. S—

23
an

TABLE 3. (Continued)

 

 

 

 

LEAD I II III
PCBITION R P L S R P. L S R P L S
DOG NUMBER
A unanesth. Q Q - - Qs qs qs qS qs S Qs S
A anesth. q - - - S S S S S S S S
B unanesth. S q q S qS S qS S qS S qS (13
B anesth. q - - - S S S S S S S S
C unanesth. Q q Q qs QS qS Q3 qS S S QS S
C anesth. q q q q S S S S S S S S

IEAD a‘v'R aVL all?
A unanesth. S_ S S S Q Q §_ Q qs qS qs S
A anesth. S S Q Q Q Q Q Q s s _ S S
B unanesth. q Q S q S Q q S qS S qS S
B anesth. S S Q Q Q q q I s s s S
C unanesth. S S _S_ S Q Q Q q Q8 8 Q8 S
C anesth. S.- S_ Q Q Q q q Q S S S S

 

KEYFCETABLE3:

q Indicates presence of a Q wave

s Indicates presence of an S wave
qs Indicates presence of both waves

- Indicates absence of both waves

Q or 8 Indicates a deep deflection ( > 3 m.)

S Indicates an 8 wave between an R wave

and an R '

* Dog was dying during the tracing, cause unknown.

30

P and T Waves and ST Segment.

 

It was further desired to point out any interrelationships of
the repolarization deflections (ST segnent and '1' wave), or their
dependence on preceding depolarization activity (QIB complex).
Influence of position on these deflections and the P wave was
also considered. In order to evaluate the tracings in these re-
spects, P and T waves and ST segments were tabulated according to
direction and amplitude. Since it was desired to somewhat quanti-
tate such statements as ”small deflection” and ”large deflection” ,
arbitrary standards were (employed in the tabulation (Table 11).
More refined measurement was not considered warranted in this case,
due to relatively large variability previously reported (15). The
arbitrary groups were felt to be adequate for qualitative or semi-
quantitative comparisons, and were based on apparent groupings of
data upon preliminary examination.

Spatial Vectors ; Transitional Pathway.

 

QRS and T spatial vectors are gaining more and more popularity
as a means of diagnosing cardiac abnormalities. The frontal plane
proJections (i.e. the QRS and T mean axes) of times are much less
infomtive, as will be pointed out later. Since it was antici-
pated that the vectors might show noml variations from time to
time, or variations due to anesthetic, spatial Q38 and T vectors
were determined for all the trained dog tracings (unanesthetized,
and anesthetized lat and 2nd runs) (Fig. 6). The location of the
transitional pathway would be expected to indicate cardiac shifts,

since it is related to the spatial orientation of the vectors.

31

II III
PTST PTST PTSI‘ PTS‘I‘ P‘I‘ST

I

Amplitude and Direction of P and T Waves and ST Segment.
PTm

LEAD
DO} PCBITION

 

 

musk

DDDD
UUUU
5555

quI
DDdD
DDDD

UUUu
dddd

fifiDD

DDDD
fiUUU
.UuUnUwu

DDDD
UUUU
«Unufiuu

IIII

IIII
UUuU

RPLS

 

5555
TTTT
UUUU

UUUU
IIII
IIdI

UUUU
quu

DDDD

5555
TITT
UUUU

5555
DTTT
UUUU

IIII
dIII
UUUU

RPLS

 

DDD
UUU
UUU

«UUU
DDD
DDD

DDDD
UUUU
UUUU

.5555
UUUU
UUUU

dDdd
UUUU
UUUU

RPLS

 

 

dddd
TTTT
UUfifi

IIII
dddd
fiddD

IIII
TTTT
DDDD

dddd
uuUU
UUUfi

dddI
uTTT
5355

IIII
dddd

uUUI

RPLS

10

 

IIII
UUUU
UUUU

IIII
IIdd
uuuu

IIII
DDDD
DDDD

IIII

uUUU
IIII

IIII
UUUU
UUUU

IIII
uuuu
UUUU

RPLS

11‘

 

IIII
TTTT
UUuu

IIII
ddId
IIIu

IIII
TTTT
DDDD

IIII

HTTT
uuuu

IIII
TTTT
UUUU

uuuu
DDdd
UUUU

RPLS

12

32

TABLE h. (Continued).

HI

H

I

IMD

Dm NMHW

PTST PTM PTST PTM PTST

PTM

 

RPLS

B

 

III
uTT
555

III
dII
dII

III
IuT
DDD

IIII
uuTT
5555

IIII
TuTT
5555

IIII
IdII
uUUU

RPLS

M

 

IIII
5555
5555

111.1

DDDD
dddd

IIII
DDDD
DDDD

IIII
5555
5555

111d
5555
5555

1111
1.111
uuuu

RPLS

5

 

IIII
5555
5555

.1111
Dddd
TTud

IIII
dDDD
DDDD

IIdd
5555
5uU5

IIId
5555
5555

11.1.5
TTuu
UUUu

RPLS

m

 

IIII

5555
5555

111.1.
DDDD
dIdi

IIII
DDDD
DDDD

IIII
5555
5555

IIII
5555
5555

1111
ddII
uuun

RPLS

U

 

IIII
5555
UUUU

IIIU

DDDD.

dIdd

IIII
DDDD
DDDD

III-l.

UUUU
UUuu

.1qu
UuUU
5555

1111
IIII

UUUU

RPLB

m

 

qu
qu
qu
qu

IIII
dddd
IIdI

IIII
TITT
DDdD

qu
qu
qu
qu

IIII
TTTT
5555

IIII
dddd
uuuu

RPLS

H

 

DDDD
5555
5555

IIII
dddd
dddd

5555
dddd
dddd

DDDD
5555
5555

DDDD
5555
5555

11.11
dIId
quu

RPLS

m

E

 

(Continued).

TABLE h.

I' II III

LEAD

PTST

P T ST P T ST

P T ST

DOG POSITION P T ST

P T ST

 

TITITIT.
m.u u_T
nunununu

.1.1.1.1
dIId
.d.1.1.d

IIII
quT
DDDD

IIII
.T ununu
"envnvnu

TITIT.T.
m.m.nonu
wunuaunu

vivivxvx
.d.1 u.1
uuuu

Duvauau

22

 

.1.Q.Q.Q
"U u unu
”U u uuu

T.T+T.T.
Dddd
.1 u_1.d

TITITITI
Idad
nuauaynu

dddd
nononvnv
"U ununu

.1.1.d.d
"ensue".
"04040wu

IIII
dIdI
uuuu

Dunxvuna

23

 

dddD
"U u unu
u u unu

TIT_u u

.dddd

.i.i.d.1

IIII
dddd
dddd

aunununu
nununu u
ununuuu

Txvxvivi
nunonon.
"ensue".

IIII
ddII
uuuu

Puvxvuno

2h

 

5 d I u d I D u I u I I u d I
I u I d d I u T I

u d I
u.T I

A anesth.

u

unanesth.

u u I .

 

.111
.d_1
.1 u

IT.
dd
dd

u T I
u I I

B anesth.
unanesth.

 

U’T I
u T I

II
Id
In

II
TT
UD

.dI

TI
Rd

.1.1
TT
"Unu

C anesth.
unanesth.

 

II
.QI
5T.

.1.1
Dd
none

u d I
u d I

D anesth.
unanesth.

 

u d I
u I I

E anesth

unanesth.

 

u --- very small upward deflection
'5 --- average upward deflection

5'--- very large upward deflection

KEY:

d --- very small downward deflection

D --- average downward deflection
5 --- very large downward deflection

I --- isoelectric (no deflection)

T --- diphasic deflection

3h

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DOO Unaaesthetised Anesthetized Anesthetized
lot has and Run
1' -12 'r 40"
A T 7 0° '
\10Rs 65‘ 0R8 6I' 0R5 di’
8 T 62' E e
T 79. QRS 53' T 9|. 0R8 68
QRS 68'
T i79‘ T -75° T 430' a
C NR: 4l' 0R840' 0R8 55'
T 400' T -98‘ T 432'
D
0R3 72' 088 72' 0R8 74‘
E
T 91- be T loo-‘47 1:030 4»
CBS 59' CBS 78' 088 68q
F
T new” 72- T BOA“ 72- T ”0' Ass 72°
FIG. 6. Spatial CBS and T Vectors - Trained Dogs.

 

 

35

It may be defined as that path formed by the intersection of the
chest and a plane which is located at the base of, and perpendic-
ular to, the QRS vector or the T vector, as the case may be. The
QRS and.T transitional pathways were determined for the position-
al dogs and the trained dogs (Tables 5 and 5b), in an attempt to
show influence of positional changes or anesthetic on cardiac
orientation.

Intervals.

PR, QRS and.QT intervals were measured for the positional and
for the trained dogs (Table 6). These intervals have been con-
sidered of importance in ECG studies because of their relation-
ship to cardiac impulse conduction time. The PR interval is in-
dicative of the time required for the impulse to travel from the
sine-atrial node through the atrio.ventricular node and bundle of
His and its branches to tie ventricular PurkinJe system. The QRS
interval indicates the time required for the wave of depolariza-
tion to pass throughout the ventricular myocardium. The QT inter-
val is indicative of the entire period of repolarization of the
ventricles, the phenomenon being mainly reflected in the T wave.
This interval also corresponds somewhat to the period of ventric-

ular systole.

36

TABLE 5.

DEFLECTION

Location of the transitional pathway for’QRS or T.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

176 indicates that the pathway
(anatomically) of lead‘Vg.

(anatomically) of lead‘vl;

0,133 'I'
”FESTTIfifiI
R P L s R P L s

DOG l 1 4 3

5 fVl rvl fVl V1 V6 V6 1V6 V6

6 r71 1 Va fill 75 v6 3 V6 " v5 ‘
7 rv1 " v1 .173 v8 ..v2 71 .Va ‘76 1V6 ’ V6 3 V6 '-

8 er 4 Ve Va .V2 7.5L .v2 1V6 1V6 ’ 1V6 ’- 1V6 ‘7’

9 W1 4 er 71 W1 v2 ”1 Va 3 V1; 4 V11 1
10 W1 4 ivl v1 v1 .va‘ Va Va .172 2. v2 5 v2 4
11 rvl “ :vl Pvl 1‘71 ’ 1V6 1V6 1 1V6 ' 1V6 1
12 r71 N1 Pvl rvl 1V6 1V6 L 1V6 3 1V6 4
13 z-v1 4 er W1‘ W1 75 V6 5’- 1V6 4 V6 2
11 N1 rv1 i-vl 1‘71 v2 ”h It 1 Vt ..v5 4 1757;
15 r71 4 v1 .153L Va .72 v1 ..v8 1V6 1V6 " 1V6 4 1V6 '
16 :v1 4 er W1 W1 1V6 1V6 ’ 1V6 4 1V6 ‘
17 :v1 ivl v,5L i-v1 1V6 1V6 2' 1V6 4 1V6
18 N1 4 rvl 1‘71 1:111 1V6 1V6 1' 1V6) 4 t v
19 £1 4 rv1 r-vl er v5 v6 4 V6 1V6 z
‘r— 3 41 2
2O r51 rWi r51 rfli 1N3 1N3 1N6 lflg
22 Pvl rv1 i-v1 :vl ' v5 V6 1 1V6 1V6
23 WI 4 ivl rv1 rvl 1V6 1V6 3 1V6 4 1V6 '
2h r51 rvl rv 1 rVi 1N5 1N3 3 1V6 4 INS
KEY: Pvl indicates that the pathway is located to the right

is located to the left

"Type" given in body; "Rank” given by number in upper

right corner.

37

A blank indicates no rank could be given.

TABLE 511. Location of QRS and T Transitional Pathways.

Dog Unanestheti zed Anesthetized Anesthetized

 

 

 

 

 

 

1st run lst run 2nd run ,
QRS T QBS T QRS -T
A Va 1V6 Va V6 Va 1V6
(Va) (V12 4713) **
B r71 1V6 i-vl 1V6 er 1V6
f (V9'v10) (Vin)
C Va V6 Va V6 V1.Va V5

”10““) (V12)

 

 

 

 

 

 

D Wl' - :v1 v5 W1 7,,
(Va) (V1512)

E V1 1V6 rvl V6 W1 V6
(VB-v9) (v1.2)

F er Vh Vl-Va Ve-Vh Vl-Va vlL
(VIC-Na) (7),)

 

 

 

 

 

** Parenthesis indicate the additional chest positions noted

in the text by ”Anesthetized - Run 3".

38

TABIE 6. PR, one And QT Intervals (in seconds);

Heart Rates; Supine Position.

 

D00 PR 0113 QT Heart Rate
5 0.12 0.01 0.21 '71
6 0.10 0.01 0.20 170
7 0.09 0.01 0.20 110
8 0.11 0.01 0.20 160
9 0.10 0.05 0.21 130

10 0.10 0.01 0.17 187

11 0.10 0.01 0.20 130

12 0.11 0.01 0.21 115

13 0.10 0.01 0.20 108

11 0.10 0.01 0.21 115

15 0.09 0.01 0.19 113

16 0.10 0.01 0.20 157

17 0.11 0.01 0.22 117

18 0.12 0.01 0.22 76

19 0.09 0.01 0.22 112

20 0.10 0.01 0.20 117

21 0.09 0.03 0.20 110

22 0.08 0.01 0.18 170

23 0.09 0.03 0.20 135

21 0.10 0.01 0.23 92

39

TABLE 6. (Continued).

 

 

 

DOG PR QRS QT Heart Rate __
A lst Run 0.09 0.01 0.22 75
unanesth.
B " 0.11 0.05 0.23 61
C " 0.10 0.01 0.19 91
D " 0.09 0.01 0.20 90
E " 0.13 0.01 0.22 105
F " 0.11 0.01 0.20 119
.A let Run 0.09 0.01 0.20 101
anesth.
B ” 0.11 0.05 0.23 91
C " 0.13 0.01 0.25 71
D “ 0.10 . 0.01 0.21 117
E " 0.13 0.05 0.22 107
F " 0.13 0.01 0.22 91
A 2nd Run 0.10 0.03 0.20 103
anesth.
B " 0.11- 0.05 0.21 82
C ” 0.13 0.05 0.25 87
D " 0.10 0.01 - 0.22 100
E " 0.12 0.01 0.22 112
F " 0.11 0.01 0.23 78

1O

DISCUSSION AND CONCLUSIONS

Major Q, R i or S Deflection Amplitude.

 

Positional Dogs.

Table 2 is a summry of ”t" tests which were made on the data
of table 1. All combinations of positions were compared by per-
forming the "t" test on the differences between values of the two
positions in question for the positional dogs. From sixteen to
nineteen values for each lead and position were used. In a few
cases, a lead had been omitted, or was marred by artifacts. The
table "t” value for fifteen to eighteen degrees of freedom at the
0.05 level is 2.10 to 2.13. Any values of ”t" greater than 2.13
weie called significant, as indicated by an underline in table 2.
In such cases, the two positions in question were deemed signifi-
cantly different in their influence on the ECG.

Position caused a significant change in amplitude of the major
ventricular deflection only when the dog was switched from the
right side to supine (or vice versa) in lead aVR, and when switch-
ed from the right side to prone (or vice versa) in lead aVL.
(Table 2). In the case of bipolar leads, significant changes
occurred when the position was changed from right side to left
side, right side to supine, prone to left side and prone to supine
in lead I, and from right side to supine in lead III. 0n the
whole, it wouldappear that no predictable effect due to positional
change occurs. It might be speculated, however, that the heart

rotates in a clockwise direction (looking from an apex perspective)

11

TABLE 2. "t" Values for Comparison of Positional Effects on
Q ,R or' S Deflections.

 

POSITIOIB RvsP RvsL RvsS vaL vaS LvsS

 

LEAD
aVR 1.13 0.69 +2.12 0.81 1.78 0.97
aVI. +325 0.26 0.06 1.12 1.78 0.16
an? 0.13 0.26 1.72 . 0.81 1.18 0.05
I < 1.0 +3.28 +_5_._6_7_ +:_2_._2_8_ +3116 +2.02
II (1.0 (0.2 (1.0 (1.0 <1.0 <1.0

 

KEY: + or .. refer the relationship between the positions,
(4- indicates that the first named position gave
the greater value numerically).

Underlined values indicate a significant difference
between positions.

The sample size for the tetest was 16 - 19; the table
”t“ was 2.10 to 2.13 at the 0.05 level.

R- rt. side; L-left side; P-prone; S-supine.

11a

L '-\.—"' .‘

 

1'

a.

when the position changes from right side to prone, and in a
counter-clockwise manner with a right side to supine position-
a1 change (Fig. 8). If this is true, then lead sVL (Fig. 8b)
would “see” more of the left ventricle with the animal in the
right side position than in the prone position. ‘Lead.aVL would
be expected to record a larger negative "QRS" deflection in the
right side position than in the prone position, according to the
"zonal interference” theory (19). (According to the theory, as
noted above, depolarization occurring in a zone “proximal” to a
given lead will record a negative deflection in that lead, and
the magnitude will be related to the quantity of myocardium.in-
valved). This was the case (Table 2). Similarly, lead aVR (Fig.
8a) would "see“ more of the left ventricle with the animal on its
right side than when supine. A larger negative deflection in aTR
would be expected with the animal on its right side. This also
was the case (Table 2). Since no other instances of significant
difference occurred, the other cases for the unipolar leads could.
not be tested according to this proposal.

using the same type of reasoning for lead I, the four cases of
significant difference were analyzed, The augmented unipolar limb
leads avn and aTL are approximately related to lead I by the ex-
pression: lead I : 2/3(aVI. - aVR) (Goldberger - 2). Since the
constant (2/3) affects aTL and aVR equally, it is omitted from con-
sideration in the following discussion of mutual influence of aVL
and aYR on the direction and relative amplitude of the QRS deflec-

tions in lead I. Considering the above relationship, the right

12

  
  
  
  

int vena cava

Posterior

(R. to Supine)

(R. to Supine)

(b) aVL “secs“

FIG. 8. The Dog Heart - Right and Left Views.

 

 

 

h3

side position should produce a larger positive deflection than the
supine position. (That is, lead I = (e minus Q ) :9 for the
right side, and lead I = (6 minus 5 ) = t for the supine position.
Such was the case (Table 2). Similarly, if the rotation of the
heart is clockwise with a body position change from prone to the
left side, TL would "see” more of the left ventricle in the prone
position, and YRwould "see” more Of the left ventricle in the left
side position. Lead I would be expected to record a larger posi-
tive deflection with the animl on its left side. This was not the
case. However, if it is further assumed that two positional forces
are interacting to produce a given deflection, viz. , (1) rotation
of the heart and (2) simple shifting of the heart from side to side,
or up and down, this discrepancy may be reconcilable. That is, the
latter force might be assumed to have a greater effect than the
former when considering left side versus prone or supine positions,
due to a restricted left-wise rotation of the heart. If this is
true, aVL would record a larger negative deflection and aTR wcnld
record a smaller negative deflection from the left side, as oppos-
ed to the prone position. Lead I should record a larger positive
deflection with the animal prone than with it on its left side.
This was the case (Table 2).

Considering prone and supine positions for lead I, it would be
premmed that the rotation of the heart has a greater influence
than mere shifting. Lead aVL would then record a larger negative
deflection from a prone than from a supine position. Lead I would

record a larger positive deflection with the dog in the prone
than in the supine position. This was the case. On the other

11

hand, when the right versus the left positions are considered,
shifting of the heart from side to side would be expected to
have a greater influence than rotation. In this event, lead
an. would record a larger negative deflection for the left side
and aVR would record a larger negative deflection for the right
side. Lead I should record a larger positive deflection for the
right side than for the left side. This was the case (Table 2).

The only other case of significant positional influence was
for right side versus supine in lead III. According to the pro-
posal above, lead aVI. would ”see" more of the left ventricle with
the animal in the supine position. If it is assumed that lead
a7! is less influenced by positional changes than are aVL and
aVR (as is indicated in table 2), then lead III should record a
larger positive deflection with the animal in tin supine position.
This was the case.

while these preposals appear to explain satisfactorily all
seven cases of significant positional effects, it must be empha-
sized that they are speculative, and could be given more emphasis
if more cases of significance had been found. While those remin-
ing cases do not discount the proposals, they serve to verify the
observation that positional effects on the ECG cannot always be
predicted for unipolar or bipolar limb leads.
Trained Dogs.

There was no predictable relationship or variation between trac-
ings taken with the dogs trained, unanesthetized or with them anes-

thetized. Furthermore, day to day variation in lightly

15

anesthetized animals was not predictable (Table lb). However,
variation due to either factor was not great, except in a few
instances, with the dogs in the supine position.

Petersen and co-workers (22) reported similar findings in
1951. As indicated by earlier investigators, (10, 12, l5, 17),
control tracings for any experimental studies would certainly
seem advisable. The supine position yields reasonably small
variations from time-to.time, and at the seine time is best suit-
ed for most experimental work. On this basis, it seem advis-
able to recommend that the supine position be employed for such
studies.

Frequency of Occurrence of Q and S Waves.

 

Positional Dogs.

Position has no predictable effect on amplitude or frequency
of occurrence of Q or S waves in leads aVF, II or III. In lead
I, however, Q waves were recorded most frequently (751» of tin
cases) with the dog on its right side (Table 3). They were sel-
dom found with the animl in the supine position or on its left
side (25% and 5% respectively). This observation is verified by
a comparison of leads TR and VI. simultaneously. Since lead I =
2/3(aVL - aVR), whenever an 1611' wave appears in aVR, associated
with a deep Q in aVL, one would expect to find a Q wave in lead I.
This occurred in 72$, 25% and 25% of the cases (Table 3) with the
animal on its right side , prone, and on its left side respective-
ly, which is in good agreement with lead I data. If Nahum's

interference theory (15) is applied in this case, along with the

further observation that no deep Q waves were present in lead aVF,

16

some generalizations might be made. Since a shift of the heart

to the right side from the left causes an initial small positive
deflection to appear in aVR, the initially active ventricular

zones have apparently moved into the distal region of this lead.
According to the proposed theories of order of excitation, (6,

18, 19 and 21), the first sepents to be depolarized are the mid-
anterior septum and anterior right ventricle. If the apex of the
heart is tipped to the right when tm animal is placed on its right
side, the initially active segments could move into tin distal
region of lead aVR (Fig. 8a). Since the proposals agree, it might
be assumed that the heart is tipped significantly in switching the
dog from the left side to the right side position. These findings,
along with the observations made above, (Major Q, R or S Amplitude)
seem to support the conviction of others that the dog's heart is
quite mobile (9, 12, 17).

The statement by Lalich, gt al.. (10) that whenever a Q wave is
present, especially a deep Q, an inverted T wave frequently follows
in lead I, was not confirmed (Tables 3 and h). The same disagree-
ment was expressed by Ionbard and Uithan (15). Furthermore, the
present work indicates that Q waves appear in leads I and II with
about equal frequencies, and are most often deepest in lead I
(Table 3). S waves were seldom recorded in lead; I , but appeared
in 99$ of the cases in lead II, and in 100% of the tracings, some-
times tagether with a Q wave, in lead III.

Trained Dogs.
Q waves were found in 65$ of the tracings taken on unanesthetiz-

ed positional dogs (A, B and C) for leads I, II, III and aVF

1*?

(where the major deflection is usually upright) (Table 3).
When the dogs were anesthetized with 30 rug/kg body wt. of
sodium pentobarbital, Q waves appeared in only 12% of the
tracings for these leads. No other effects of anesthetic

were apparent from table 3.

P and T Waves and ST Segments.

 

Bipolar lead amplitudes for P and T waves and ST segments
can be predicted quite accurately from unipolar lead data
(Table h), as was expected according to theory, but the con-
verse is certainly not true. Such bipolar data are therefore
considered to be extraneous, and are also mch less informa-
tive than unipolar data (2).

Position has little effect on the P or T waves or the ST
segment in unipolar lead tracings. When deviation does occur,
it is random.

When the ST segment was depressed in leads II, III and aVF,
it was usually accompanied by a deep S wave. This may indicate
“interference" between depolarization and repolarization poten-
tials occurring in different segments simultaneously, and has been
reported to occur in all the unipolar leads with a relatively high
frequency (15). The fact that it occurred in these three leads
indicates that the primary region involved is that proximal to
lead aVI". The influence on the ST segment in leads II and III is

presumed to be dependent on the fact that they both involve aVF.

1&8

Anesthesia (20 mg/kg. body wt. of sodium pentobarbital) has no
predictable effect on the P or T waves or the ST segment for any
of the limb leads. The only changes noted were slight , and of a
random nature.

Intervals and heart Rates.

Little difference was found between durations of PR, QRS or QT
for any of the above studies, in spite of a considerable variation
in heart rates (Table 6). Lower rates did produce slightly longer
PR and QT intervals, as was expected, but the effect was not appre-
ciable, indicating that most of the variation was reflected in the
T-P isoelectric segment. Mean interval lengths (in seconds) along
with their standard deviations, for the 26 positional and trained
dogs, were: PR : 0.102 0.01h

ops -.-. 0.01m 0.00h
and QT = 0.207 0.017.
These means are consistent with those reported by others (1+, 5,
15), but the variations were lower.

The tachycardia reported by Lalich, Walker and Cohen (11), due
to sodium pentobarbital, has been confirmed for 30 nag/kg. body wt.
of the anesthetic. However, 20 mg/kg body wt. yields approximate-

ly normal heart rates.

1+9

Precordial Leads

 

Chest electrode placement, as described above differed from
the scheme used by Lombard 8t Witham (15). While this may have
led to a different pattern of T waves, it was not expected to
yield significantly different QRS patterns. These authors, how-
ever, noted that chest leads could be classified into three gen-
eral types, viz., a large troup (7a) in which the transitional
pathway of QRS involved V1 and/or Y2; a smaller group (21%) in
which the pathway involved V3 and/or Vt and a, very small group
(11%) in which the pathway involved V5 and/or V6. The classifi-
cation is explained above, under ”Results".

Using the same method of ('typing” for the positional dogs,
and for trained dogs, (anesthetized and unanesthetized) (Fig. 5),
the following observations were made.

1. QRS Complex.

Two classifications were employed. (1) The tracings were
”typed" according to Lombard's method, (as explained above, und-
er 'REULTS”), for each position. (2) The positions were "ranked”
according to the one in which the transitional pathway was locat-
ed farthest to the left (called #1), and. the one in which it was
located farthest to the right, (called #h). These locations were
determined from the six chest leads, by observing the 12.3 pattern.
The point at which there was a change from a large R wave - smll
8 wave pattern to a moderate R wave - 8 wave pattern, wtmre approx-
imately half of the QB area was above, and half below the iso-

electric line, corresponds with the location of tlm transitional

50

pathway (see examples, FIG. 5b). Left and right as used above
refer to the anatomical location on the dogs chest (FIG. It).

If more than one position failed to show a transitional pathway,
but did show the characteristic approach to a pathway (see FIG.
5b), that position which indicated the least tendency for transi-
tion was called #1.

(a) 1128 Transitional Pathway.

Right Prone Left Supine
Lead: V1 V1 V1 V 2
Rank: 14 3 2 l

(b) r Transitional Pathway.

Bight Prone Supine
Lead: V1, V5 V6 V6
Rank: 1 2 h 3

FIG.:9. Examples of Classification by Bank.

The classification by rank is further clarified in figure 9.
In example 9a, the QRS transitional pathway was indicated in
lead V1 of the left side tracing, and in lead V2 of the supine
tracing. It was not present in any of the leads of the right

side or prone tracings, but the V1 pattern of the prone tracing

51

tracing indicated close proximity to a pathway. The V1
pattern of the right side tracing indicated that the path-
way was probably located quite a distance to the right of
lead.V1. 0f the four positions, the right side showed the
right-most location of the pathway, the prone position was
second to this, the supine position third, and the left side
showed the leftamest location. The positions were ranked
accordingly.

1.1 Positional Degs.

1.11 Classification by Type.

Three general types could be ascertained, viz. (l).A large
group was found (95% of right side, 79% of prone, 53% of left
side and.7h$ of supine records) in which the transitional path-
way could not be found in any of the six leads employed, but was
indicated to be located somewhere to the right of lead‘Vl (desig-
nated rvl) (Table 5). (2) A smaller group occurred (0% of right
side, 16% of prone, 32$ of left side and 2h$ of supine records)
in which the pathway involved V1 and/or Va. ( 3) A small group
occurred (0% of right side, 5% of prone, 16% of left side and 5%
of supine records) in which the transition was located between
Va and‘Ve. In two cases, the transition could not be determined.
The electrode placements are given in figure h. These results
differ from those of Lombard and Witham, principally in the large
group where no pathway could be found. Indications are that it
would have appeared in a lead located to the right of‘Vl, had such

a lead been employed. The largest group reported by Lombard and

52

Witham showed a transition involving V1 and/or Va‘ It is possi-
ble that if Vl had been located one centimeter farther to the
right of the midline, these results and those of Lombard would
have agreed. However, as stated above, electrode placement was
believed to be identical in both studies for V1,. Va and V2. In
any case, the discrepancy is not a great one, and seems to indi-
cate desirability of additional electrodes to the right of V1 if
the chest leads are to be useful in the Grant and Estes Method of
interpretation (3).

1.12 Classification by "Bank".

The second classification indicated that the transitional path-
way was located farthest right most frequently when the animal was
in the right side position (631; of the cases). The transitional
pathway which was located farthest left could not be ascribed with
any degree of certainty to any of the remaining positions, nor
could any intermediate location of the patmay be determined.

2 test was run on the data, and indicated that the right side

A 1
position gave significantly different results from those of the
other positions (0.01 level).
1.2 Trained Dogs.
1.21 Anesthetized vs. Unanesthetized Degs.

The types were identical in four of six cases (2 cases of Va,
2 cases of N1) whether anesthetized or not, indicating no shift
in the transitional pathway due to anesthesia. In the other two

cases, variation indicated a random shift due to anesthetic. In

no case was the shift of appreciable magnitude.

53

1.22 Day-to -Day Variation in Anesthetized Dogs.

The tracings were essentially identical for the QBS complex in
five of six cases, regardless of the time interval between records.
In the other case (Dog B) a slight shift to the right was noted in
the second tracing. .Apparently day-to-day effects have little or
no influence on the Q38 transitional pathway.

1.23 Additional Chest Leads.

In an effort to determine where the pathway does exist in those
cases where tracings indicate an rvl location, the trained.dogs
were anesthetized a third.time. Six.new chest positions were trac-
ed, (along'with‘va and‘vh as controls). The third run agreed per-
fectly with the second run in those cases where the transitional
pathway had been located to the left of VI (dogs A, c and r) (Fig.
5b). In the other three cases, where an rvl location had been in-
dicated by the second run, the pathway was indeed identified at the
right of lead V1 by examination of tracings V8 (deg D); in another,
it was located between V8 and‘V9; (dogIE); and in the third case,
it was located between v9 and vlo (dog 13). On the basis of these
findings, the positions'V8 and'V9 and/or'Vlo would appear to be
desirable additions to previously reported leads, when precordial
leads are taken, since they would aid in more definitely establish-
ing the spatial vector in many cases. The importance of the latter
has already been discussed.

2. "T" Wave.
Two classifications analagous to those described for the QRS

complex were used, viz. , according to "type" or ”rank”. In the

511-

latter case, the position in which the transitional pathway was
found farthest right was labeled #1, and that in which the path-
way was located farthest left was labeled #h. (See examples,
FIG. 9b). In cases where the pathway could not be located, but
was indicated to exist to the left of V6, the position with the
largest T wave in V6 was labeled #h. Other positions were rank-
ed between these two extremes when possible.

2.1 Positional Dogs.

2.11 Classification by Type.

Application of the first classification disclosed that all
data could be described by four "types” (Table 5). (a) a rather
large group (h7% of right side, 53% of prone, 58% of left side
and h7% of supine records) occurred in which the transitional
pathway could not be found, but was indicated to be located sene-
where to the left of V6. (b) A smaller group (32% of right side,
32% of prone, 21% of left side and 32% of supine records) occurred
in which the pathway was located at V5 pr V6. (c) A smll group
(5% of right side, 11% of prone, 5% of left side and 11% of supine
records) was found in which the pathway was located somewhere in
the interval between 72 and V5, (d) A small group (5% of right
side, 5% of prone, 5% of left side and 5% of supine records)
occurred in which the pathway involved Va and/or V2.

It is apparent from these observations that additional elec-
trode(s) to the left of V6 might be desirable in order to ascer-
tain the transitional pathway for the "T" vector.

2.12 Classification by "Rank”.
When tracings were "ranked", according to the second classifica-

55

tion, it was found that the transitional pathway for T is located
farthest right most frequently with the animal in the right side
position (100% of the cases); was located farthest left with the
animal in the left side position (63% of the cases); and inter-
mediate ranking was randomly divided between the prone and supine

positions . A Xe

test showed the second statement to be signifi-
cant at the 0.01 level. These findings are entirely in agreement
with possible shifting of the heart, and reinforce the statement
of earlier investigators ( 9, 12, 15) that the dog‘s heart is quite
mobile.

2.2 Trained Degs: Additional Chest Leads.

As noted above, a number of cases were observed in which the T
wave transitional pathway was apparently located to the left
(anatomically) of v6. Additional leads were added (v12, v13 and
Vlh) to extend the previous scheme diagonally downward and to the
left, in an effort to locate the pathway in the cases mentioned
above. Leads Va and V}, were also included as controls.

The third run agreed quite well with the second run as to
”type” in those cases where the transitional pathway had been
located to the right of V6 (Dogs C, D, H and F, Table 5b).

In the two cases where the pathway was indicated to be located
to the left of V6 by run two, it was found in the additional chest
leads of run three (712313 for dog A and V1,, for dog B).

In the case of dog 3, however, lead V6 showed approximately the

same proximity to the pathway that V11, did, and V or 13 did not

12
confirm the location of run two, hence a shift of T vector between

56

runs was indicated, and no conclusions could be drawn from the
observations. It is suspected that the lesser incidence of loca-
tion of the pathway to the left of V6 for this study versus that
previously done on the positional dogs was due to the lighter
state of anesthesia (2O mg/kgfiembutal) used in the trained dog
studies compared to deep anesthesia Bang/kg.) used for positional
studies. On the basis of the latter, however, it would seem de-
sirable to include one electrode to the left of V6 (on the dorsal

side) and perhaps in line with 7h: V5 and V6, in order to be cer-

 

tain of including the transitional pathway of the T wave spatial
vector in the leads traced.

Spatial Vectors .

 

l. QRS Vector.

From the Q33 vectors, (Fig. 6) it can be observed that the
”within dog” variation was usually smll regardless of state or day-
to-day effects (the widest range being 18° in the frontal plane
projection between the anesthetized and unanesthetized records of
Dog E). It should be noted, however, that this much variation in
the frontal plane projection is not necessarily a good measure of
vector variation for reasons to be discussed later under "T"
Vector. The variation "between dogs" was larger.

2. ""13“I Vector.

From superficial examination of the frontal plane projection,
both ”within dog" and "between dogs" variation appear larger. For
example, the shift a... 179° to 45°, which indicates a 106°

range (Dog C, unanesthetized vs. anesthetized, FIG. 6). Closer

57

 

 

 

examination of the three dimensional figure, however, illustrates
an important point. The mean T axis values in the frontal plane
by theuelves are worthless in those cases wl'mre the vector is
approaching a perpendicular to that plane. This is more clearly
illustrated by Fig. 7, which shows enlarged three dimensional rep-
resentations of the three T vectors for deg C . Pencils have been
drawn to indicate that the vector points almost straight toward
the viewer. It can be understood that a mll change in the three
dimensional orientation of the pencil (vector) represents a large
change in the frontal plane projection. From this illustration it
can be seen that the apparent "large shift” encountered in deg C
is, in reality, only a small change in vector direction. This
emphasizes the fact that the chest leads should be analyzed along
with the mean axis in order to ascertain the vector direction,
especially in those cases where the vector approaches a perpendic-
ular to the frontal plane. As the vector approaches the frontal

plane, the mean QRS or T axes become more meaningful.

 

179 a -750

a T axis (frontal plane projection)

J
P5!

Vectors - 000 C

 

SUMRY

Electrocardiogram were taken on twenty normal mongrel dogs
which.were anesthetized with sodium pentobarbital, and on six
other dogs which were trained to lie quietly during the proced-
ure. iEffects of position, anesthesia, and timeato-time varia-
tions were determined. Three preposals were made from QRS ampli-
tude data. (1) The heart may rotate in a clockwise direction
with a supine to right side to prone change in position, and
counterclockwise with the reverse change. (2) The heart may
also shift from side to side, and up and down at the same time.
(3) These two forces both influence the ECG to some degree when
changes in position are made. The effects of position changes
on the major deflection of the QRS group are not reliably pre-
dictable.

Q,waves were frequently found in lead I with the animal on
its right side and seldom occurred with the animal on its left
side. The mobility of the heart is implicated.'

Q waves occurred in 65% of the tracings taken on unanesthetiz-
ed dogs (leads I, II, III and.aVI). The frequency was reduced
to 12% when the animals were anesthetized, indicating a suppres-
‘ sing influence of sodium pentobarbital on Q waves.

Effect of position or anesthesia on the P and T waves and ST
segment were slight, and unpredictable.

Depression of the ST segment in leads II, III and avr was
usually accompanied by a deep S»wave indicating possible ”inter-

ference" between depolarization and repolarization potentials

59

occurring simultaneously in different ventricular segnents.

The heart rate has a slight influence on PR and QT intervals.
Most of the differences in heart rate are "absorbed” by the iso-
electric T-P segment, however. Mean PR, Q18 and QT‘intervals are
given for the twenty.six dogs. I

Sodium pentobarbital in large doses (30 mg. /kg. body wt.)
induces tachycardia, but in light doses (20 mg. /kg.) yields
approximately normal heart rates.

Determination of QRS and T spatial vectors and transitional
pathways from precordial lead data indicate the desirability of
using several additional chest electrodes. TWO or three elec-
trodes in addition to V1 were proposed for the right chest (QI'S
pathway) and one additional electrode was proposed for the left
chest (T pathway). The electrodes to be located to the right of
V1 might be located (1) in the third intercostal space one centi-
meter to the right of the right nipple line, (2) in the right mid-
axillary line on a horizontal line with (l) , and (3) midway be-
Ween (1) and (2). The additional left-chest electrode might be
located on a horizontal line with vh, v5 and v6, and about one-
third of the distance between the left mid-axillary line and the

mid -dorsal line .

60

"—'-‘-—I

 

1.

2.

10.

11.

13.

1h.

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