Isorhythmic atrioventricular dissociation in an alert normothermic cat.

Isorhythmic AV dissociation with dynamic PR intervals can occur in alert normothermic cats with cardiomyopathy.

This case report documents an unusual presentation of isorhythmic atrioventricular (AV) dissociation in an 11-year-old male neutered Birman cat presenting with pyelonephritis. Clinical examination revealed gallop sounds and bradycardia. Laboratory findings showed mild azotaemia and marked neutrophilia consistent with urinary tract infection. Transthoracic echocardiography identified a non-specific cardiomyopathy phenotype with biatrial enlargement. Electrocardiographic findings were distinctive, showing wide QRS complexes, bradycardia, and dissociation between atrial and ventricular electrical activity. The arrhythmia demonstrated an initial phase of fixed synchronization with consistent PR intervals, subsequently evolving to variable PR intervals on a beat-to-beat basis. The final diagnosis was isorhythmic AV dissociation type I with characteristics mimicking type II pattern, accompanied by ventricular depolarization exhibiting left bundle branch block morphology. This case is notable for the atypical presentation of AV dissociation in an alert, normothermic cat and the dynamic nature of the PR interval variations observed during serial evaluations.

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