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The electrocardiogram in dogs with standardized body and limb positions
J. ELECTROCARDIOLOGY, 1 (2), 175-182, 1968
The Electrocardiogram in Dogs with Standardized Body and Limb Positions * JOliN D. IIILL, D.V.~I., ~I.MED. SCI.t
SUMMARY
MATERIALS AND METHODS
Ten lead electrocardiograms were recorded from 70 normal dogs in the right lateral recumbent position with carefully standardized foreleg positions. The 70 dogs included 25 different breeds plus mongrels whose ages ranged from 10 weeks to 12 years. Excessive skewness was present in the majority of the electrocardiographic measuremcnts. In some cases in which skewness was minimal, the distribution was bimodal. There was considerable variation in the mean electric axis of thc T wave in the 3 planes and in the direction of the T wave in individual leads except that thc T wave was primarily negative in lead VIO and positive in lead CVsRL from all the dogs except one. In the frontal plane, the QRS mean electric axis fell between +45 and +90 degrees in 83 % of the dogs, while somewhat greater .variation was noted in the transverse and sagittal planes.
The dogs were free of cardiovascular disease as determined by clinical examination. Lateral and dorso-ventral radiographs of the thorax were taken in 23 % of the animals and no cardiac abnormalities were found. The electrocardiograms were free of conduction disturbances and arrhythmias except for sinus arrhythmia, which is commonly associated with respiration in the dog. The tracings Were not evaluated for mean electric axes or amplitudes until after the dog had been selected as a normal control. All electrocardiograms were recorded from unanesthetized dogs in the right lateral recumbent position with the legs, head and neck positioned as though the dog were standing upright on all four limbs" Special attention was given to positioning the forelegs parallel to each other and vertical to the long axis of the body and to keeping the head and neck flat on the table. Alligator clips, fastened to the lead cables, were clipped to the skin after applying dilute electrode paste. Recordings were made with a Cambridge Versa-Scribe at a paper speed of 25 mrn.zsec. and sensitivity of 1 cm.Zmv. The standard bipolar limb leads I, II and III, and augmented unipolar limb leads aVR, aVL and aVF were recorded. Unipolar chest leads as developed for the dog by Lannek!' and modified by Detweiler and Patterson'? were also recorded. Wilson's central terminal was used as the indifferent electrode and the exploring electrode positions on the thorax were as follows (Fig. 1): CV 6 left lower (CV 6LL) on the left sideat the sixth intercostal space at the edge of the sternum; CV 6 left upper (CV 6LU) at the level of the costochondral junction in the same intercostal space; V IO over the seventh thoracic spine; CV s right lower (CV:.RL) on the right side at the fifth intercostal space just to the right of the sternum. These leads correspond to low VI, low V~, V IO and low VI in human electrocardiography. The complexes selected for measurement were
INTRODUCTION
The position of the forelegs has not been controlled in past electrocardiographic studies in normal dogs l - Is. Detweiler l6.17 and Cagan l 8 •19 have pointed out that foreleg position has a marked effect on the canine electrocardiogram. This effect is statistically significant in the interprctation of electrocardiograms and vectorcardiograms from research animals". This report provides normal canine electrocardiographic data recorded with standardized body and limb positions using a 10 lead system. • From the Comparative Cardiovascular Studies Unit, Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pa. 19104 Supported in part by grants from the National Heart Institute (HE-4885-07) and American Heart Association (65-G-31).
t This work was done while a Post-Doctoral Fellow in Cardiology, National Heart Institute, u.s.r.lI.s. (5-F2-HE-22,838-03); presently, Post-Doctoral Fellow in Ph}'siology, U.S.P.B.S. Training Grant 5TOI-GM00957.
176
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n.
IIILL
( . \ I -"
®
Fig. I. Right lateral recumbent radiograph from a normal dog illustrating the location of the tho racic leads in relation to the heart. Lead CVR .L in A,lead CV 6LL in B,lead CV 6LU in C, and lead V, O in D. See methods for details. chosen when possible from areas of the recording in which the preceding and following T-P intervals were exactly on the same level. In those cases were the tracings were not level, a number of complexes were measured and averaged. The complexes were not selected for any specific period of respiration. All the measurements were made under 3 power magnification. The amplitude of upward deflections was measured from the upper contour of the base-line, and for downward deflections from the lower contour of the ba se-line. Amplitudes were measured to the nearest 0.05 rnv. and durations to the nearest 0.01 sec. In the statistical analyses, "n" represented the number of observations made and not the number of electrocardiograms studied. Relative observation frequencies (%) were based on the total popu-
lation of 70 electrocardiograms. The P and T waves were grouped into five classes: positive, isoclectric, negative and diphasic of the \-/ type and - / type.
+
RESULTS Twenty-five different breeds of dogs plus mongrel s (Table I) were repre sented by 43 males and 27 fem ales whose ag es ranged from 10 weeks to 12 years. Seventeen dogs were under I year of age, 40 animals ranged from 1 to 6 years of age and 28 dogs were over 6 year s old. The max imum P wave was +0.25 mv, in leads aVF and CVGLU (Table 2), whereas the largest negative P wave was -0.10 mv. in leads VIO and CV ;;RL. The tracings were occasionally isoelectric in the region of the P wave in leads I, VIO and
177
I:CG IN DOGS
CV;,RL. Diphasic P waves were present in lead CVsRL from 3 dogs. In most leads, the I' wave was po sitive except for negative waves in leads V IO (38.6%) and CV;,RL (10.0%). The P wave mean electric axis in the frontal plane ranged from 1-18 to +90 degrees; in the transverse plane it fell between 0 and +90 degrees for 38 dogs and between -18 and -90 degrees for 32 dogs; and
the left sagittal plane ranged between 0 and +45 degrees for 37 dogs and from -12 to -45 degrees for 33 do gs. There was considerable variation in the direction of th e T wave among dogs even though the position of the forelegs was standardized (Table 2). The only exception was lead CV;;RL with positive T waves from 69 animals and only 1 negative T
TABLE 1 Breed distribution of the 70 normal dogs Breed
Number
Beagle Boston Terrier Boxer Chesapeake Day Retr iever Chihuahua Cocker Spaniel Dalmation English Bulldog English Seller Foxhound German Shepherd Irish Seller Keeshond
6 1 5
Breed
Number
Labrador Retriever Mongrel Newfoundland Pekingese . Poodle Sarnoyed Siberian Husky Springer Spaniel St. Bernard Toy Manchester Terrier Weimaraner Welsh Terri er Wire-Ha ired Fox Terrier
1
3 3 2 4 3 1
4 I
3
1 16 1 1
3 1 2 1 2 1 1 1
2
TABLE 2 The amplitude of positive and negative I' and T waves in millivolts from 70 normal dogs with standardized body and limb positions. aVF
VIO
CV6LU
CV~RL
100.0 0.050.25 0.15 0.133 0.0037
47.1 0.050.10 0.05 0.055 0.00023
100.0 0.050.25 0.10 0.126 0.0029
72.9 0.050.15 0.05 0.065 0.00073
Positive P lmres
Relative frequency Range Median Mean Variance
97.1 0.050.15 0.05 0.063 0.00084
Negative P wares
10.0 0.050.10 0.05 0.066
38.6 0.050.10 0.05 0.059
Relative frequency Range Median Mean Variance
O.OOO-l
.---- ---------- ----------------------------- -------------- ----------- ------- -----------Positive T 1I'(lres Relative frequency Range
Median Mean Variance Negative T lmres Relative frequen cy Range Median Mean Variance
44.3 0.050.25 0.05 0.071 0.002
45.7 0.050.45 0.20 0.186 0.012
8.6 0.050.20 0.05 0.075
65.7 0.050.90 0.25 0.320 0.048
98.5 0.050.80 0 .30 0.346 0.037
51.4 0.050:25 0.05 0.095 0.003
45.7 0.050.60 0.25 0.236 0.019
87.1 0.050. 40 0.20 0.211 0.006
15.7 0.050.35 0.25 0.236
1.5 0.15
178
J. D. IIlLL
wave from a 3-month-old Sarnoyed, The tracings were rarely isoelectric in the region of the T wave. Diphasic T waves occasionally occurred in leads aVF and CV 6LU, and the amplitude did not exceed 0.50 my. in either direction. The largest T wave amplitude was +0.90 my. in lead CVtLU, whereas the maximum negative T wave was -0.60 my. in lead aVF. In the frontal plane the T wave mean electric axis ranged from 26 to 180 degrees (35 dogs) and from - 45 to -147 degrees (35 dogs); in the transverse plane it fell between 0 and +162 degrees (65 dogs) and from - 26 to -135 degrees (5 dogs); and the left sagittal plane ranged between 0 and 158 degrees (64 dogs) and -9 to -161 degrees (6 dogs). The QRS mean manifest electric axes are illustrated in Figure 2, in which the dog is viewed ventrally in the frontal plane, cranial to caudal in the transverse plane and standing on all four legs in the left sagittal plane. This method of viewing the dog follows Helm's" suggestions for maintaining trigonometric functions and keeping the zero point constant at the 3 o'clock position
+
+
+
in all three planes. The range of the frontal plane axes was 0 to 102 degrees with 83 % of the dogs in the range of +45 to +90 degrees. In the transverse plane, the axes varied in a clockwise direction from - 31 to 90 degrees with 89 % of the dogs in the range of 0 to +90 degrees. The sagittal plane axes ranged clockwise from - 21 to \-90 degrees with 90 %of the animals in the range from o to +90 degrees. A Q wave was a frequent finding in all leads with two exceptions (Table 3). No Q waves were present in lead CV ~R L in any of the tracings examined, and one small Q wave was present in lead aVR from the only Irish Setter in the study. The maximum Q wave amplitude of 1.20 my. was found in leads II and VIO• A QS wave was present in lead VIO from I mongrel dog, while an R wave was recorded in all leads for the remaining 69 dogs. The maximum R wave was 5.40 my. in lead CV 6LU and the maximum S wave was 2.30 my. in lead aVR. These peak values were recorded from 2 of the 3 English Setters in the group. In the limb leads, the largest R wave was 3.0 my. in lead II. An S wave was not present in
+
+
FRONTAL
TRANSYERSE
.,,,< RIGHT
OQRS:'L
-90·
~
LEFT
±,eo' +-----*~,.,.,.---_+o.
LEFT SAGITTAL DORSAL
-90·
CRt.....:AL
CAUDAL
ileo' +------;r---;-:o-"F--::-..-::--+ o·
+90· VENTRAL
Fig. 2. A graphic representation of the mean manifest electric axes of the QRS complex found in normal dogs. The dogs were in the right lateral recumbent position with carefully standardized limb positions. The percentage figures refer to the relative frequency in each wedge and are rounded ofT to thenearest whole number.
[CO IN
179
noes
TABLE 3 A mplitude s of th e QRS complex in millivolts from 70 normal dogs with standard ized body and limb po sition s lead:
II
Q I I'{/\'(' Relative frequ ency 90.0 Ra nge 0.05M edian Mean
Variance" R Imr('
0.60 0.15 0.22 0.022
98. 6 0.051. 20 ' 0. 30 0.38 0.075
III
87. 1 0.051.00 0.25 0.27
nVF
CVtLL
CV.LU
97. 1 37. 1 0.05-0.051.05 0.65 0.25 0.30 0.31 0.30 0.032ot 0.052
40.0 0.050.35 0.05 0.09 O.ooot
81.5 100.0 0.05 0.150.55 1.20 0.15 0.65 0.17 0.65 0.013 0.057
aVR
1.5 0.30
0.~6
aVL
Re lative frequency 100.0 Ra nge O.IDMedian M ean Variance' S ware
100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.45-0.250.250.2D0. 500.050.051.50 3.00 2.35 2.40 5.40 0.70 0.90 4.00 0.60 1.60 1.35 1.90 0 . 25 0.15 1.90 1.10 0.6ot 1.97 1.61 1.12 1.37 1.96 0.27 0.23 0.117 0.334 0.366 0.828 0.2ot7 0.593 0.032 0.~ 2
V,.
98.6 0.050. 80 0. 30 0.31 0.0286
CV~RL
non e
100.0 0.153.60 1.00 1.11 0.449
Relative frequency Range Medi an Mean Va rianc e'
8.6 0;05
32.9 0.050.35 0.15 0.16 0.009
3·t.) 100.0 0.050.1 50.70 2.30 0.20 1.10 0. 22 1.09 0.029 0. 223
64.3 0.101.10 0.40 0.42 0.054
35.7 0.050.55 0.\0 0.16 0.014
80.0 0.051.60 0. 30 0.39 0.093
5ot.3 0.051.30 0.20 0. 28 0.067
none
100 .0 0.051.60 0.60 0.67 0.156
• Standard dev iations arc not listed because of the number of asymmetrical distribut ions found in this seri es.
lead V10 in any of the trac ings examined. In six different breeds, S waves of 0.05 mv. occurred in lead I. Although an S Wave was always present in leads aVR and CV;;RL, it occurred less than 36 % of the time in leads II, III and aVE Only one S' wave was encountered and it occurred in lead a VL. An R' wave was present in lead aVR from 9 dog s, lead a VL from 8 do gs and lead CV 6LL from I dog. The R' waves did not exceed 0040 my. in amplitude. The lead II inter vals were as follows: P-R range 0.07 - 0.14 sec., mean 0.099, S.D. ± 0.008; QRS rang e 0.03 - 0.06 sec., mean 0.041, S.D. ± 0.009; and Q -T ran ge 0.15 - 0.25 sec., mean 0.203, S.D. ± 0.024. Th e mean heart rate was 117 per minute and the range was 60 - 160 per minute. Of a total of 60 electrocardiographic parameters analysed , excessive skewn ess to the right was present in 32 and only 4 were mark edly skewed to the left. While skewness was not significant in 24 electrocardiographic parameters, some of these had bimodal frequency distributions". The various frequen cy distributions found in the electrocardiographic parameters examined are illustrated
in Figure 3. The Q wave in lead VI O repr esents a relatively no rmal distribution without significant skewness as determined by the value of Beta, as given by Cro xton" , Th e R wave in lead aVF was not significantly skewed; it was, however, bimod al. The R wave in lead aVL was very significantly ske wed to the right , while the QRS mean electric axis in the frontal plane was significantly skewed to the left. DISCUSSION Detweiler and Patte rson'? reported that the direction of the T wave was not of diagnostic significance except in lead s CV;;RL and VIO. In their study, negat ive T waves did not occur in lead CVsRL in normal dogs of most breed s over two months of age, whereas in lead VIO negative T waves were common in most breeds excep t the Chihuahua. The present study confirms these findings, in that the T wave was negative in 61 of 70 dogs (87.1 %) in lead VIO and po sitive in 69 of 70 dogs (98.5 %) in lead CV;;RL. Andre'" and Lannek!' have stated that the QR S mean elect ric axis of the do g is so wide that it is not clinically useful. In contrast , Lombard and Whitham' ? found the frontal plane mean QRS axis to be between +41 and I 20 degree s in 45
+
180
J. D. JIILL
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fRONTAl. PLANE ELECTRIC
ORS MEA"I
AXES
MANIFEST
1"1 DEGREES
Fig. 3. An illustration of the various types of frequency histograms found in the electrocardiographic parameters examined. Class intervals are at 0.05 mv. in A and C, 0.35 mv, in nand 15 degrees in D. In A, the Q wave in lead VIO is a relatively normal distribution without significant skewness (Beta, = 0.0268, P > 0.10); and in B, the R wave in lead aVF is not significantly skewed but is bimodal (Beta, = o.o·nG, P > 0.10). In C, the R wave in lead aVL is significantly skewed to the right (Bctaj = 2.91H8, l' < 0.02), while in D, the frontal plane QRS mean electric axis is significantly skewed to the left (Beta I = 1.24-18, P < 0.02),
of 50 anesthetized dogs, even though they did not control limb positions. Detweiler and Patterson'? noted that in 60 normal dogs in the right lateral recumbent position with controlled limb positions, the mean QRS axis in the frontal plane usually fell between +45 and 100 degrees. The present study also disagrees with the findings of Andre and Lannek in that 58 of 70 (83 %) dogs had frontal plane QRS axes between I- 45 and +90 degrees. Although numerous reports have appeared on electrocardiographic findings in normal dogs 1- 1>,
+
many have been ancillary reports in conjunction with other studies and were based on results from a small number of animals. Other reports on larger numbers of dogs often used only bipolar limb leads or bipolar and augmented unipolar limb leads, while studies including chest leads have used various electrode positions and lead systems. Past studies also have employed a variety of body positions and have failed to control the position of the forelegs, a factor now known to be important 17- 2o• Crawley and Swenson" have reviewed the results of previous major reports and
ECG IN DOGS
Brooyruans" has discussed the need for standardization of electrocardiographic methods in animals. At the present time, the standard bipolar limb leads I, II, III and the augmented unipolar limb leads aVR, aVL and aVF appear to be well established. For the chest leads, the unipolar method using Wilson's central terminal for the indifferent electrode is the preferred method". The locations of the exploring electrode in the thoracic leads as established by Lannck!' have been useful clinically. The standing and sitting positions in the dog usually give unsatisfactory tracings as a result of muscle tremors. In the awake untrained dog, the supine position is not well tolerated. The prone position can be used, but it is difficult to restrain an uncooperative animal. The right lateral position is usually well tolerated and has the advantage that limb positions can be controlled carefully by an assistant Lannck!' reported significant skewness in some electrocardiographic measurements in dogs. In the present study, excessive skewness was present in the majority of measurements and where skewness was minimal, the distribution was often bimodal. These factors complicate the establishment of normal values for the electrocardiogram of the dog. Values derived from standard deviations (implying a symmetrical distribution) based on asymmetrical distributions arc too narrow at the long end and too wide at the short end. The additional assumption of a Gaussian distribution further compounds the error. The problem of skewness also effects electrocardiographic measurements from man and has been thoroughly discussed by Simonson'". In view of Simonson's studies employing larger population samples, it is unlikely that the skewness in this study would be offset by a larger sample. In addition to body and limb positions and skewness, chest conformation must also be considered in determining normal limits. Detweiler!" noted that the QRS electrical axis varies with body conformation. Gonirr' reported that narrowchested dogs have a more constant and vertical axis, while broad-chested "dogs have a more horizontal and variable heart axis. The Collie, French Poodle and German Shepherd breeds have a narrow thorax and a more vertical electrical axis, while the Cocker Spaniel and Doxer breeds have an intermediate electrical axis and a broader thorax. The Dachshund breed is an exception
181
with a broad thorax and more vertical axis. The number of dogs in each breed in the present study was too small to confirm or refute the findings of these researchers.
ACKNOWLEDGEMENTS The author wishes to express his appreciation to Dr. D. A. Abt for assistance in the statistical analyses and to Mr. R. Iannuzzi for technical assistance. The author is indebted to Drs. D. K. Detweiler and E. N. Moore and other members of the Comparative Cardiovascular Studies Unit for their helpful advice and criticism.
REFERENCES 1. Burman, S. 0., Panagopoulos, P., and Kahn, S.: The electrocardiogram of the normal dog. 1. Thoracic and Cardiovascular Surg. 51: 379, 1966. 2. Clark, C. H., and Wallace, C. R.: Canine Elt:etrocardiography. Auburn Vet., Fall: 19, 1957. 3. Gonin, P.: Uber die Lage der elcktrischen Herzachse beirn Hund, lnaug. Diss., Bern, 1962. 4. Grollman, A., Mcl.ean, 1. A., Muirhead, E. E., and Scurry, M. M.: Electrocardiogram of the normal dog and its alteration in acute malignant hypertension induced by bilateral nephrectomy. Am. 1. Physiol, 169: 74, 1952. 5. Gyarmati, E.: Klinische elektrokardiographische Untersuchungen bei Hunden. Vet. Med. Diss., Budapest, 1939. 6. Harris, B. R., and Hussey, R.: The clectrocardiographic changes following coronary artery ligation in dogs. Am. Heart 1. 12: 724, 1936. 7. Haupt, K.: Die Aufnahmetechnik des Bundec1ektrokardiogrammes in der Veteriniirklinik und ihrc Ergebnisse. Vet. Med. Diss., Giessen, 1929. 8. Horwitz, S. A., Spanier, M. R., and Wiggers, \Y. C.: The electrocardiogram of the normal dog. Proc. Soc. Exper. Bio\. and Med. 8~: 121, 1953. 9. Too, K., and Umemoto, H.: Studies on clinical applications of electrocardiogram on dogs. I. Electrocardiogram of Shepherd dogs and Karafuto (Saghalien) dogs. Jap. J. Vet. Res. 7: 215, 1959. 10. Lalich, 1., Cohen, L., and Walker, G.: The frequency of electrocardiographic variations in normal, unanesthetized dogs. Am. Heart J. 22: 105, 1941. II. Takahashi, M.: Experimental studies on the electrocardiogram of the dog. Jap, 1. Vet. Sci. 26: 191, 1964. 12. Peterson, E. 5., Ricketts, H. T., Brewer, H. R., Lints, H. A., Test, C. E., and Tupikova, N. A.: Electrocardiogram of the Beagle dog. Proc, Soc. Exp. Diol. and Med. 77: 330, 1951. 13. Soave, O. A.: Clinical electrocardiograms of the dog. Am. 1. Vet. Res. 15:336, 1954. 14. Lannck, N.: A Clinical and Experimental Study of the Electrocardiogram in Dogs. Med. Clin. Royal Vet. College, Stockholin, 1949. 15. Lombard, E. A., and Witham, c.: Electrocardiogram of the anesthetized dog. Am. J. Physio\. 181: 567,1955. 16. Detweiler, D. K.: Cardiovascular disease in ani-
182
17. 18. 19. 20.
21. 22.
J. D. HILL
mals: Clinical considerations. In: Cardiology. Luisada, A. A., Ed., New York. McGraw-Hill, 1961, Vol. 5, Section 27, pp. 10-42. Detweiler, D. K., and Patterson, D. F.: The prevalence and types of cardiovascular disease in dogs. Ann. N.Y. Acad. Sci. 127: 481, 1965. Cagan, S.: Prispevok k Electrokardiograrnu u psa, Bratislavsk. Lek. Listi. 39: 540, 1959. Cagan, S., and Barta, E.: Die Bedingungen des konstanten Elektrokardiogrammes beim Hunde. Ztschr. f. Kreislaulforsch. 48: llOl, 1959. Hill, J. D.: The significance of foreleg positions in the interpretation of electrocardiograms and vectorcardiograms from research animals. Am. Heart J. 75: 518, 1968. Helm, R. A.: Vectorcardiographic notation. Circulation 13: 581, 1956. Hill, J. D.: A Correlative Study of Right Ventricular Conduction Disturbances in the Dog. Master's Thesis, Graduate Division- of Medicine, Universityof Pennsylvania, 1967.
23. Croxton, F. E.: Elementary Statistics with Applications in Medicine and the Biological Sciences. New York, Dover Publications, Inc., 1959. 24. Andre, T.: Enlargement of the heart with congestive heart failure in dogs. Nord. Vet-Med. 7: 90S, 1955. 25. Crawley, G.-J., and Swenson, M. J.: The canine electrocardiogram prior to and following production of cardiac lesions. Vet. Med.jSm. Animal Clin. 61: 363,1966. 26. Brooymans, A. \Y. M.: Standardization of leads in veterinary clinicalelectrocardiography. Tijdschr, Diergeneesk. 79: 801, 1954. 27. Criteria Committee of the New York Heart Association: Diseases of the Heart and Blood Vessels. Nomenclature and Criteria for Diagnosis. Sixth edition. Boston, Little, Brown and Company, 1964, p. 386. 28. Simonson, E.: Differentiation Between Normal and Abnormal in Electrocardiography. SI. Louis, The C. V. Mosby Co., 1961, p, 33.
The Electrocardiogram in Dogs with Standardized Body and Limb Positions * JOliN D. IIILL, D.V.~I., ~I.MED. SCI.t
SUMMARY
MATERIALS AND METHODS
Ten lead electrocardiograms were recorded from 70 normal dogs in the right lateral recumbent position with carefully standardized foreleg positions. The 70 dogs included 25 different breeds plus mongrels whose ages ranged from 10 weeks to 12 years. Excessive skewness was present in the majority of the electrocardiographic measuremcnts. In some cases in which skewness was minimal, the distribution was bimodal. There was considerable variation in the mean electric axis of thc T wave in the 3 planes and in the direction of the T wave in individual leads except that thc T wave was primarily negative in lead VIO and positive in lead CVsRL from all the dogs except one. In the frontal plane, the QRS mean electric axis fell between +45 and +90 degrees in 83 % of the dogs, while somewhat greater .variation was noted in the transverse and sagittal planes.
The dogs were free of cardiovascular disease as determined by clinical examination. Lateral and dorso-ventral radiographs of the thorax were taken in 23 % of the animals and no cardiac abnormalities were found. The electrocardiograms were free of conduction disturbances and arrhythmias except for sinus arrhythmia, which is commonly associated with respiration in the dog. The tracings Were not evaluated for mean electric axes or amplitudes until after the dog had been selected as a normal control. All electrocardiograms were recorded from unanesthetized dogs in the right lateral recumbent position with the legs, head and neck positioned as though the dog were standing upright on all four limbs" Special attention was given to positioning the forelegs parallel to each other and vertical to the long axis of the body and to keeping the head and neck flat on the table. Alligator clips, fastened to the lead cables, were clipped to the skin after applying dilute electrode paste. Recordings were made with a Cambridge Versa-Scribe at a paper speed of 25 mrn.zsec. and sensitivity of 1 cm.Zmv. The standard bipolar limb leads I, II and III, and augmented unipolar limb leads aVR, aVL and aVF were recorded. Unipolar chest leads as developed for the dog by Lannek!' and modified by Detweiler and Patterson'? were also recorded. Wilson's central terminal was used as the indifferent electrode and the exploring electrode positions on the thorax were as follows (Fig. 1): CV 6 left lower (CV 6LL) on the left sideat the sixth intercostal space at the edge of the sternum; CV 6 left upper (CV 6LU) at the level of the costochondral junction in the same intercostal space; V IO over the seventh thoracic spine; CV s right lower (CV:.RL) on the right side at the fifth intercostal space just to the right of the sternum. These leads correspond to low VI, low V~, V IO and low VI in human electrocardiography. The complexes selected for measurement were
INTRODUCTION
The position of the forelegs has not been controlled in past electrocardiographic studies in normal dogs l - Is. Detweiler l6.17 and Cagan l 8 •19 have pointed out that foreleg position has a marked effect on the canine electrocardiogram. This effect is statistically significant in the interprctation of electrocardiograms and vectorcardiograms from research animals". This report provides normal canine electrocardiographic data recorded with standardized body and limb positions using a 10 lead system. • From the Comparative Cardiovascular Studies Unit, Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pa. 19104 Supported in part by grants from the National Heart Institute (HE-4885-07) and American Heart Association (65-G-31).
t This work was done while a Post-Doctoral Fellow in Cardiology, National Heart Institute, u.s.r.lI.s. (5-F2-HE-22,838-03); presently, Post-Doctoral Fellow in Ph}'siology, U.S.P.B.S. Training Grant 5TOI-GM00957.
176
J.
n.
IIILL
( . \ I -"
®
Fig. I. Right lateral recumbent radiograph from a normal dog illustrating the location of the tho racic leads in relation to the heart. Lead CVR .L in A,lead CV 6LL in B,lead CV 6LU in C, and lead V, O in D. See methods for details. chosen when possible from areas of the recording in which the preceding and following T-P intervals were exactly on the same level. In those cases were the tracings were not level, a number of complexes were measured and averaged. The complexes were not selected for any specific period of respiration. All the measurements were made under 3 power magnification. The amplitude of upward deflections was measured from the upper contour of the base-line, and for downward deflections from the lower contour of the ba se-line. Amplitudes were measured to the nearest 0.05 rnv. and durations to the nearest 0.01 sec. In the statistical analyses, "n" represented the number of observations made and not the number of electrocardiograms studied. Relative observation frequencies (%) were based on the total popu-
lation of 70 electrocardiograms. The P and T waves were grouped into five classes: positive, isoclectric, negative and diphasic of the \-/ type and - / type.
+
RESULTS Twenty-five different breeds of dogs plus mongrel s (Table I) were repre sented by 43 males and 27 fem ales whose ag es ranged from 10 weeks to 12 years. Seventeen dogs were under I year of age, 40 animals ranged from 1 to 6 years of age and 28 dogs were over 6 year s old. The max imum P wave was +0.25 mv, in leads aVF and CVGLU (Table 2), whereas the largest negative P wave was -0.10 mv. in leads VIO and CV ;;RL. The tracings were occasionally isoelectric in the region of the P wave in leads I, VIO and
177
I:CG IN DOGS
CV;,RL. Diphasic P waves were present in lead CVsRL from 3 dogs. In most leads, the I' wave was po sitive except for negative waves in leads V IO (38.6%) and CV;,RL (10.0%). The P wave mean electric axis in the frontal plane ranged from 1-18 to +90 degrees; in the transverse plane it fell between 0 and +90 degrees for 38 dogs and between -18 and -90 degrees for 32 dogs; and
the left sagittal plane ranged between 0 and +45 degrees for 37 dogs and from -12 to -45 degrees for 33 do gs. There was considerable variation in the direction of th e T wave among dogs even though the position of the forelegs was standardized (Table 2). The only exception was lead CV;;RL with positive T waves from 69 animals and only 1 negative T
TABLE 1 Breed distribution of the 70 normal dogs Breed
Number
Beagle Boston Terrier Boxer Chesapeake Day Retr iever Chihuahua Cocker Spaniel Dalmation English Bulldog English Seller Foxhound German Shepherd Irish Seller Keeshond
6 1 5
Breed
Number
Labrador Retriever Mongrel Newfoundland Pekingese . Poodle Sarnoyed Siberian Husky Springer Spaniel St. Bernard Toy Manchester Terrier Weimaraner Welsh Terri er Wire-Ha ired Fox Terrier
1
3 3 2 4 3 1
4 I
3
1 16 1 1
3 1 2 1 2 1 1 1
2
TABLE 2 The amplitude of positive and negative I' and T waves in millivolts from 70 normal dogs with standardized body and limb positions. aVF
VIO
CV6LU
CV~RL
100.0 0.050.25 0.15 0.133 0.0037
47.1 0.050.10 0.05 0.055 0.00023
100.0 0.050.25 0.10 0.126 0.0029
72.9 0.050.15 0.05 0.065 0.00073
Positive P lmres
Relative frequency Range Median Mean Variance
97.1 0.050.15 0.05 0.063 0.00084
Negative P wares
10.0 0.050.10 0.05 0.066
38.6 0.050.10 0.05 0.059
Relative frequency Range Median Mean Variance
O.OOO-l
.---- ---------- ----------------------------- -------------- ----------- ------- -----------Positive T 1I'(lres Relative frequency Range
Median Mean Variance Negative T lmres Relative frequen cy Range Median Mean Variance
44.3 0.050.25 0.05 0.071 0.002
45.7 0.050.45 0.20 0.186 0.012
8.6 0.050.20 0.05 0.075
65.7 0.050.90 0.25 0.320 0.048
98.5 0.050.80 0 .30 0.346 0.037
51.4 0.050:25 0.05 0.095 0.003
45.7 0.050.60 0.25 0.236 0.019
87.1 0.050. 40 0.20 0.211 0.006
15.7 0.050.35 0.25 0.236
1.5 0.15
178
J. D. IIlLL
wave from a 3-month-old Sarnoyed, The tracings were rarely isoelectric in the region of the T wave. Diphasic T waves occasionally occurred in leads aVF and CV 6LU, and the amplitude did not exceed 0.50 my. in either direction. The largest T wave amplitude was +0.90 my. in lead CVtLU, whereas the maximum negative T wave was -0.60 my. in lead aVF. In the frontal plane the T wave mean electric axis ranged from 26 to 180 degrees (35 dogs) and from - 45 to -147 degrees (35 dogs); in the transverse plane it fell between 0 and +162 degrees (65 dogs) and from - 26 to -135 degrees (5 dogs); and the left sagittal plane ranged between 0 and 158 degrees (64 dogs) and -9 to -161 degrees (6 dogs). The QRS mean manifest electric axes are illustrated in Figure 2, in which the dog is viewed ventrally in the frontal plane, cranial to caudal in the transverse plane and standing on all four legs in the left sagittal plane. This method of viewing the dog follows Helm's" suggestions for maintaining trigonometric functions and keeping the zero point constant at the 3 o'clock position
+
+
+
in all three planes. The range of the frontal plane axes was 0 to 102 degrees with 83 % of the dogs in the range of +45 to +90 degrees. In the transverse plane, the axes varied in a clockwise direction from - 31 to 90 degrees with 89 % of the dogs in the range of 0 to +90 degrees. The sagittal plane axes ranged clockwise from - 21 to \-90 degrees with 90 %of the animals in the range from o to +90 degrees. A Q wave was a frequent finding in all leads with two exceptions (Table 3). No Q waves were present in lead CV ~R L in any of the tracings examined, and one small Q wave was present in lead aVR from the only Irish Setter in the study. The maximum Q wave amplitude of 1.20 my. was found in leads II and VIO• A QS wave was present in lead VIO from I mongrel dog, while an R wave was recorded in all leads for the remaining 69 dogs. The maximum R wave was 5.40 my. in lead CV 6LU and the maximum S wave was 2.30 my. in lead aVR. These peak values were recorded from 2 of the 3 English Setters in the group. In the limb leads, the largest R wave was 3.0 my. in lead II. An S wave was not present in
+
+
FRONTAL
TRANSYERSE
.,,,< RIGHT
OQRS:'L
-90·
~
LEFT
±,eo' +-----*~,.,.,.---_+o.
LEFT SAGITTAL DORSAL
-90·
CRt.....:AL
CAUDAL
ileo' +------;r---;-:o-"F--::-..-::--+ o·
+90· VENTRAL
Fig. 2. A graphic representation of the mean manifest electric axes of the QRS complex found in normal dogs. The dogs were in the right lateral recumbent position with carefully standardized limb positions. The percentage figures refer to the relative frequency in each wedge and are rounded ofT to thenearest whole number.
[CO IN
179
noes
TABLE 3 A mplitude s of th e QRS complex in millivolts from 70 normal dogs with standard ized body and limb po sition s lead:
II
Q I I'{/\'(' Relative frequ ency 90.0 Ra nge 0.05M edian Mean
Variance" R Imr('
0.60 0.15 0.22 0.022
98. 6 0.051. 20 ' 0. 30 0.38 0.075
III
87. 1 0.051.00 0.25 0.27
nVF
CVtLL
CV.LU
97. 1 37. 1 0.05-0.051.05 0.65 0.25 0.30 0.31 0.30 0.032ot 0.052
40.0 0.050.35 0.05 0.09 O.ooot
81.5 100.0 0.05 0.150.55 1.20 0.15 0.65 0.17 0.65 0.013 0.057
aVR
1.5 0.30
0.~6
aVL
Re lative frequency 100.0 Ra nge O.IDMedian M ean Variance' S ware
100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.45-0.250.250.2D0. 500.050.051.50 3.00 2.35 2.40 5.40 0.70 0.90 4.00 0.60 1.60 1.35 1.90 0 . 25 0.15 1.90 1.10 0.6ot 1.97 1.61 1.12 1.37 1.96 0.27 0.23 0.117 0.334 0.366 0.828 0.2ot7 0.593 0.032 0.~ 2
V,.
98.6 0.050. 80 0. 30 0.31 0.0286
CV~RL
non e
100.0 0.153.60 1.00 1.11 0.449
Relative frequency Range Medi an Mean Va rianc e'
8.6 0;05
32.9 0.050.35 0.15 0.16 0.009
3·t.) 100.0 0.050.1 50.70 2.30 0.20 1.10 0. 22 1.09 0.029 0. 223
64.3 0.101.10 0.40 0.42 0.054
35.7 0.050.55 0.\0 0.16 0.014
80.0 0.051.60 0. 30 0.39 0.093
5ot.3 0.051.30 0.20 0. 28 0.067
none
100 .0 0.051.60 0.60 0.67 0.156
• Standard dev iations arc not listed because of the number of asymmetrical distribut ions found in this seri es.
lead V10 in any of the trac ings examined. In six different breeds, S waves of 0.05 mv. occurred in lead I. Although an S Wave was always present in leads aVR and CV;;RL, it occurred less than 36 % of the time in leads II, III and aVE Only one S' wave was encountered and it occurred in lead a VL. An R' wave was present in lead aVR from 9 dog s, lead a VL from 8 do gs and lead CV 6LL from I dog. The R' waves did not exceed 0040 my. in amplitude. The lead II inter vals were as follows: P-R range 0.07 - 0.14 sec., mean 0.099, S.D. ± 0.008; QRS rang e 0.03 - 0.06 sec., mean 0.041, S.D. ± 0.009; and Q -T ran ge 0.15 - 0.25 sec., mean 0.203, S.D. ± 0.024. Th e mean heart rate was 117 per minute and the range was 60 - 160 per minute. Of a total of 60 electrocardiographic parameters analysed , excessive skewn ess to the right was present in 32 and only 4 were mark edly skewed to the left. While skewness was not significant in 24 electrocardiographic parameters, some of these had bimodal frequency distributions". The various frequen cy distributions found in the electrocardiographic parameters examined are illustrated
in Figure 3. The Q wave in lead VI O repr esents a relatively no rmal distribution without significant skewness as determined by the value of Beta, as given by Cro xton" , Th e R wave in lead aVF was not significantly skewed; it was, however, bimod al. The R wave in lead aVL was very significantly ske wed to the right , while the QRS mean electric axis in the frontal plane was significantly skewed to the left. DISCUSSION Detweiler and Patte rson'? reported that the direction of the T wave was not of diagnostic significance except in lead s CV;;RL and VIO. In their study, negat ive T waves did not occur in lead CVsRL in normal dogs of most breed s over two months of age, whereas in lead VIO negative T waves were common in most breeds excep t the Chihuahua. The present study confirms these findings, in that the T wave was negative in 61 of 70 dogs (87.1 %) in lead VIO and po sitive in 69 of 70 dogs (98.5 %) in lead CV;;RL. Andre'" and Lannek!' have stated that the QR S mean elect ric axis of the do g is so wide that it is not clinically useful. In contrast , Lombard and Whitham' ? found the frontal plane mean QRS axis to be between +41 and I 20 degree s in 45
+
180
J. D. JIILL
A
B '
>-
~
0
u
w &~
w
z
Z
5
r"-
w
\oJ
> 0:
lO
w
a:
"-
...J
~ < ...J
W
W
IC
10
a:
a: c
c
If'
140
'll'
Q .."o·~
....
iN'
zoo
RAV"" ••
C '"
r-
oc.
N·70
o "1·70
40 ~
u z w
W
::>
>",
o w
~..J
'0
a: u.
W
a:
w
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20
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20
4
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w
a: '0
'0
o RAve ,.
I
I
I
I
o
m.
fRONTAl. PLANE ELECTRIC
ORS MEA"I
AXES
MANIFEST
1"1 DEGREES
Fig. 3. An illustration of the various types of frequency histograms found in the electrocardiographic parameters examined. Class intervals are at 0.05 mv. in A and C, 0.35 mv, in nand 15 degrees in D. In A, the Q wave in lead VIO is a relatively normal distribution without significant skewness (Beta, = 0.0268, P > 0.10); and in B, the R wave in lead aVF is not significantly skewed but is bimodal (Beta, = o.o·nG, P > 0.10). In C, the R wave in lead aVL is significantly skewed to the right (Bctaj = 2.91H8, l' < 0.02), while in D, the frontal plane QRS mean electric axis is significantly skewed to the left (Beta I = 1.24-18, P < 0.02),
of 50 anesthetized dogs, even though they did not control limb positions. Detweiler and Patterson'? noted that in 60 normal dogs in the right lateral recumbent position with controlled limb positions, the mean QRS axis in the frontal plane usually fell between +45 and 100 degrees. The present study also disagrees with the findings of Andre and Lannek in that 58 of 70 (83 %) dogs had frontal plane QRS axes between I- 45 and +90 degrees. Although numerous reports have appeared on electrocardiographic findings in normal dogs 1- 1>,
+
many have been ancillary reports in conjunction with other studies and were based on results from a small number of animals. Other reports on larger numbers of dogs often used only bipolar limb leads or bipolar and augmented unipolar limb leads, while studies including chest leads have used various electrode positions and lead systems. Past studies also have employed a variety of body positions and have failed to control the position of the forelegs, a factor now known to be important 17- 2o• Crawley and Swenson" have reviewed the results of previous major reports and
ECG IN DOGS
Brooyruans" has discussed the need for standardization of electrocardiographic methods in animals. At the present time, the standard bipolar limb leads I, II, III and the augmented unipolar limb leads aVR, aVL and aVF appear to be well established. For the chest leads, the unipolar method using Wilson's central terminal for the indifferent electrode is the preferred method". The locations of the exploring electrode in the thoracic leads as established by Lannck!' have been useful clinically. The standing and sitting positions in the dog usually give unsatisfactory tracings as a result of muscle tremors. In the awake untrained dog, the supine position is not well tolerated. The prone position can be used, but it is difficult to restrain an uncooperative animal. The right lateral position is usually well tolerated and has the advantage that limb positions can be controlled carefully by an assistant Lannck!' reported significant skewness in some electrocardiographic measurements in dogs. In the present study, excessive skewness was present in the majority of measurements and where skewness was minimal, the distribution was often bimodal. These factors complicate the establishment of normal values for the electrocardiogram of the dog. Values derived from standard deviations (implying a symmetrical distribution) based on asymmetrical distributions arc too narrow at the long end and too wide at the short end. The additional assumption of a Gaussian distribution further compounds the error. The problem of skewness also effects electrocardiographic measurements from man and has been thoroughly discussed by Simonson'". In view of Simonson's studies employing larger population samples, it is unlikely that the skewness in this study would be offset by a larger sample. In addition to body and limb positions and skewness, chest conformation must also be considered in determining normal limits. Detweiler!" noted that the QRS electrical axis varies with body conformation. Gonirr' reported that narrowchested dogs have a more constant and vertical axis, while broad-chested "dogs have a more horizontal and variable heart axis. The Collie, French Poodle and German Shepherd breeds have a narrow thorax and a more vertical electrical axis, while the Cocker Spaniel and Doxer breeds have an intermediate electrical axis and a broader thorax. The Dachshund breed is an exception
181
with a broad thorax and more vertical axis. The number of dogs in each breed in the present study was too small to confirm or refute the findings of these researchers.
ACKNOWLEDGEMENTS The author wishes to express his appreciation to Dr. D. A. Abt for assistance in the statistical analyses and to Mr. R. Iannuzzi for technical assistance. The author is indebted to Drs. D. K. Detweiler and E. N. Moore and other members of the Comparative Cardiovascular Studies Unit for their helpful advice and criticism.
REFERENCES 1. Burman, S. 0., Panagopoulos, P., and Kahn, S.: The electrocardiogram of the normal dog. 1. Thoracic and Cardiovascular Surg. 51: 379, 1966. 2. Clark, C. H., and Wallace, C. R.: Canine Elt:etrocardiography. Auburn Vet., Fall: 19, 1957. 3. Gonin, P.: Uber die Lage der elcktrischen Herzachse beirn Hund, lnaug. Diss., Bern, 1962. 4. Grollman, A., Mcl.ean, 1. A., Muirhead, E. E., and Scurry, M. M.: Electrocardiogram of the normal dog and its alteration in acute malignant hypertension induced by bilateral nephrectomy. Am. 1. Physiol, 169: 74, 1952. 5. Gyarmati, E.: Klinische elektrokardiographische Untersuchungen bei Hunden. Vet. Med. Diss., Budapest, 1939. 6. Harris, B. R., and Hussey, R.: The clectrocardiographic changes following coronary artery ligation in dogs. Am. Heart 1. 12: 724, 1936. 7. Haupt, K.: Die Aufnahmetechnik des Bundec1ektrokardiogrammes in der Veteriniirklinik und ihrc Ergebnisse. Vet. Med. Diss., Giessen, 1929. 8. Horwitz, S. A., Spanier, M. R., and Wiggers, \Y. C.: The electrocardiogram of the normal dog. Proc. Soc. Exper. Bio\. and Med. 8~: 121, 1953. 9. Too, K., and Umemoto, H.: Studies on clinical applications of electrocardiogram on dogs. I. Electrocardiogram of Shepherd dogs and Karafuto (Saghalien) dogs. Jap. J. Vet. Res. 7: 215, 1959. 10. Lalich, 1., Cohen, L., and Walker, G.: The frequency of electrocardiographic variations in normal, unanesthetized dogs. Am. Heart J. 22: 105, 1941. II. Takahashi, M.: Experimental studies on the electrocardiogram of the dog. Jap, 1. Vet. Sci. 26: 191, 1964. 12. Peterson, E. 5., Ricketts, H. T., Brewer, H. R., Lints, H. A., Test, C. E., and Tupikova, N. A.: Electrocardiogram of the Beagle dog. Proc, Soc. Exp. Diol. and Med. 77: 330, 1951. 13. Soave, O. A.: Clinical electrocardiograms of the dog. Am. 1. Vet. Res. 15:336, 1954. 14. Lannck, N.: A Clinical and Experimental Study of the Electrocardiogram in Dogs. Med. Clin. Royal Vet. College, Stockholin, 1949. 15. Lombard, E. A., and Witham, c.: Electrocardiogram of the anesthetized dog. Am. J. Physio\. 181: 567,1955. 16. Detweiler, D. K.: Cardiovascular disease in ani-
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17. 18. 19. 20.
21. 22.
J. D. HILL
mals: Clinical considerations. In: Cardiology. Luisada, A. A., Ed., New York. McGraw-Hill, 1961, Vol. 5, Section 27, pp. 10-42. Detweiler, D. K., and Patterson, D. F.: The prevalence and types of cardiovascular disease in dogs. Ann. N.Y. Acad. Sci. 127: 481, 1965. Cagan, S.: Prispevok k Electrokardiograrnu u psa, Bratislavsk. Lek. Listi. 39: 540, 1959. Cagan, S., and Barta, E.: Die Bedingungen des konstanten Elektrokardiogrammes beim Hunde. Ztschr. f. Kreislaulforsch. 48: llOl, 1959. Hill, J. D.: The significance of foreleg positions in the interpretation of electrocardiograms and vectorcardiograms from research animals. Am. Heart J. 75: 518, 1968. Helm, R. A.: Vectorcardiographic notation. Circulation 13: 581, 1956. Hill, J. D.: A Correlative Study of Right Ventricular Conduction Disturbances in the Dog. Master's Thesis, Graduate Division- of Medicine, Universityof Pennsylvania, 1967.
23. Croxton, F. E.: Elementary Statistics with Applications in Medicine and the Biological Sciences. New York, Dover Publications, Inc., 1959. 24. Andre, T.: Enlargement of the heart with congestive heart failure in dogs. Nord. Vet-Med. 7: 90S, 1955. 25. Crawley, G.-J., and Swenson, M. J.: The canine electrocardiogram prior to and following production of cardiac lesions. Vet. Med.jSm. Animal Clin. 61: 363,1966. 26. Brooymans, A. \Y. M.: Standardization of leads in veterinary clinicalelectrocardiography. Tijdschr, Diergeneesk. 79: 801, 1954. 27. Criteria Committee of the New York Heart Association: Diseases of the Heart and Blood Vessels. Nomenclature and Criteria for Diagnosis. Sixth edition. Boston, Little, Brown and Company, 1964, p. 386. 28. Simonson, E.: Differentiation Between Normal and Abnormal in Electrocardiography. SI. Louis, The C. V. Mosby Co., 1961, p, 33.