Arrhythmia inducibility and ventricular vulnerability in a chronic feline infarction model

Abstract

Ventricular tachyarrhythmias are the cause of sudden cardiac death in ischemic heart disease. Reliable animal models are necessary to study techniques for identifying individuals at risk and to develop effective modes of therapy. The purpose of the present study was to evaluate the inducibility of ventricular tachyarrhythmias and vulnerability to ventricular fibrillation and to correlate these findings with changes in ventricular refractoriness in a chronic feline model. Twelve conditioned cats were randomly divided into two groups: group A, sham-operated controls (n = 5); or group B, permanent occlusion of the left anterior descending coronary artery (n = 7). Two weeks later, the following measurements were made: (1) assessment of refractory periods at several ventricular sites; (2) inducibility to ventricular tachyarrhythmias; and (3) determination of ventricular fibrillation threshold. After electrophysiologic testing, the animals were killed and the hearts were studied histologically. Ventricular fibrillation thresholds were significantly lower in group B compared with group A (13 ± 3 vs 46 ± 9 mA; p < 0.01). One of the sham-operated controls had induction of nonsustained ventricular tachycardia, while six of the group B animals had reproducible, inducible ventricular tachyarrhythmias ( p < 0.01). There was a significant dispersion in effective refractory periods between normal and infarcted sites in group B (46 ± 6 msec) not seen in group A (12 ± 2 msec, p < 0.01). The group A cats demonstrated minimal damage to the myocardium or cardiac architecture. Group B cats demonstrated extensive, transmural, homogeneous infarcts of approximately 30% of the anterior wall of the left ventricle. The chronically infarcted feline heart appears to be a reliable model to evaluate vulnerability to ventricular tachyarrhythmias. Moreover, temporal dispersion of refractoriness observed in infarcted animals, applicable to clinical measurement, may serve as a marker of chronic vulnerability.