998 
ANIMAL DISEASES 


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Figure 4. — Incomplete Right Bundle Branch Block 
Ten lead electrocardiogram of a 1-year old male Beagle with incomplete right bundle branch block (No. 37 in Fig- 
ure 5). The QRS interval is on the upper limit of normal for the dog (0.07 second). Terminal, delayed QRS 
forces are directed to the right, cranially, and stern ally, producing wide, notched S waves in leads I, II, III, 
AVF, and the left precordial leads CV6LL (Vs) and CV6LL (Ve). An R' wave is present in leads AVR and 
CV5RL (Vi). 
normally conducted impulse which travels 
through the AV node and bundle of His. 
Anomalous bridges between the atrium and 
ventricle have been found in patients with 
WPW.^*'^^ Epicardial activation studies have 
shown an area of preexcitation of the right 
atrioventricular margin,^® -^ and in some cases 
the syndrome has been abolished by cutting the 
right atrioventricular margin at that site.^'^^ 
These findings suggest that preexcitation in 
WPW occurs over discrete accessory AV con- 
duction pathways similar to those described by 
Kent.2«'3o However, direct electrophysiologic 
and anatomic evidence of preexcitation over a 
