D. F. PATTERSON 
999 
38 36 31 
68 69 
+ + + * 
HlKD4i<>-C>4^-CH 
+ *t * 
I I Normal Mole 
O Normal Femole 
H IR6BB (well - developed) 
on IRBBB (lesser - degree) 
+ Neonatol Deoth NO ECG 
* Sacrificed for Study 
VSD = Ventriculor Septol Defect 
PS = Volvular Pulmonic Stanosis 
Figure 5. — Incomplete Right Bundle Branch Block in 
a Family of Beagles 
A female Beagle with pulmonic stenosis and a male 
Beagle with a small ventricular septal defect pro- 
duced 7 pups with varying degrees of incomplete 
right bundle branch block (IRBBB) but no gross 
cardiovascular malformations. Both pulmonic sten- 
osis and ventricular septal defects appeared in the F2 
generation. 
Reprinted from reference #8 with permission. 
discrete atrioventricular bridge have not been 
reported in the same individual owing to diffi- 
culties in obtaining both electrophysiologic and 
anatomic data. 
The WPW syndrome has also been observed 
in dogs. In a screening survey of cardiovascular 
disease in dogs presented to a veterinary clinic, 
it was found once among 3,000 dogs examined 
electrocardiographically.31 Recently the study 
of an example of type A WPW syndrome in an 
English Cocker Spaniel dog* (Figure 6) has 
provided the long sought direct evidence of 
preexcitation of the right ventricle over a dis- 
crete AV bridge.^ In this dog, preexcitation of 
the posterior (caudal) wall of the right ventri- 
cle occurred over an anomalous atrioventricular 
bundle having a conduction velocity and histo- 
♦ By remarkable coincidence, this dog belonged to Dr. Mary Livezey, 
cardiologist and wife of the late Dr. Charles C. Wolferth, a pioneer 
in electrocardiography who with Dr. Frances Wood first demonstrated 
the existence of an anatomic bridge between the right atrium and 
ventricle in a human patient with WPW.^ Dr. Livezey's cooperation 
in making this dog available for study is gratefully acknowledged. 
logic structure characteristic of ventricular my- 
ocardium. Figure 7 shows sequence of epicardial 
activation in a dog with type A WPW syndrome. 
Disturbances of Atrioventricular Conduction 
Relatively little is known about the etiology 
or pathogenesis of congenital atrioventricular 
blocks in the dog or man, but some interesting 
observations in the dog suggest that this may be 
a fruitful subject for further study. 
James and Konde have reported extensive 
histologic studies of the sinus node and atrio- 
ventricular conduction system in a young dog 
with complete heart block. The location and 
size of the sinus node, atrioventricular node and 
His bundle were normal, but the cellular ar- 
chitecture of these structures was distinctly 
abnormal. The authors hypothesize a normal em- 
bryonic origin of this specialized conduction tis- 
sue, leading to a normal spatial arrangement, 
It ';' 
f " 
tr — 
llliiiu. 
liiiliiiiil 
AVR 
AVL 
AVF 
III 
nil 
\\ 
I 
lii 
PI 
TT 
1 
CV5RL(Vi) CV6LL(V3) CV6LU(V6) 
M 
k 
iiii 
tr- 
II 
■'II 
1 
If 
iiti 
\ 
i 
r 
Vio 
III 
iiilffilSmi^llIliiiSHill 
' 1 [|||{ 
Ilk 
il 
iiitiiiiii'ffliiii 
Figure 6.— Type A Wolflf-Parkinson-White Syndrome 
in an English Cocker Spaniel 
The P-R segment is absent in all leads and the QRS 
complex is prolonged. A delta wave can be seen best 
in leads CV6LL (comparable to V3 in man) and 
CV6LU (comparable to V6). Principal QRS forces 
are oriented to the left, toward the sternum, and 
cranially. Preexcitation of the right ventricle in this 
dog was shown to occur at the AV margin near the 
posterior (caudal) border of the right ventricle (9). 
