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Ventricular tachycardia in English bulldogs with localised right ventricular outflow tract enlargement.

OBJECTIVES
To describe the electrocardiographic characteristics of ventricular tachycardia arising from the right ventricular outflow tract and the particular association between this arrhythmia and the presence of localised right ventricular outflow tract enlargement in English bulldogs.


METHODS
Five English bulldogs were referred with a history of syncope or cardiogenic shock. In all dogs, 12-lead surface ECG, thoracic radiograph and echocardiography were collected. In all but one dog 24-hours Holter monitoring and signal-averaged ECGs was examined and in one dog electrophysiological study and radiofrequency catheter ablation of the VT substrate was performed.


RESULTS
Documented arrhythmias included a single sustained monomorphic wide QRS tachycardia in four dogs, and an alternans of two different monomorphic forms in one dog. Mean QRS duration during tachy-cardia was 91·6 ±9·83 milliseconds. QRS complexes manifested a left bundle branch block morphology and an inferior axis (81 ±13·73°). R wave notching was present in the caudal (inferior) leads in three tachy-cardias. Lead I was negative in 3 of 6, positive in 1 of 6 and isodiphasic in 2 of 6. Lead aVL was negative in 5 of 6 and positive in 1 of 6. Signal-averaged electrocardiograms revealed late potentials in three dogs. Echocardiography showed a localised right ventricular outflow tract enlargement in all dogs. Cardiac map-ping established two sites of origin of ventricular tachycardia within the right ventricular outflow tract in one dog: caudal free-wall and cranial-septal.


CLINICAL SIGNIFICANCE
The presence of a localised right ventricular outflow tract enlargement and ventricular tachycardia with left bundle branch block morphology could suggest segmental arrhythmogenic right ven-tricular cardiomyopathy in the English bulldog.