Inducible ventricular arrhythmias in a naturally occurring model of cardiomyopathy

This study examined inducibility of ventricular tachyarrhythmias in turkeys with and without naturally occurring dilated cardiomyopathy. Using a transvenously positioned electrode catheter, 32 cardiomyopathy and 12 control unsedated turkeys aged 2 to 4 months were studied by right ventricular endocardial extrastimulus testing at basic pacing cycle lengths of 200 and 170 ms with both 1 and 2 extrastimuli and burst pacing at progressively shorter cycle lengths (200 to 100 ms). Following study, a dilatation index (determined as the ratio of left ventricular endocardial and epicardial diameter at level of the apex-base midpoint) was utilized to assess the functional severity of cardiomyopathy. All control turkeys had a dilatation index less than 0.3. In cardiomyopathic turkeys, dilatation index was normal (less than 0.3) in 3/32, showed mild to moderate dilatation in 25/32 (0.3 to 0.6), and severe dilatation in 4/32 (greater than 0.6). Results showed no difference in right ventricular effective or functional refractory periods between control and cardiomyopathic turkeys. Control turkeys had no inducible ventricular tachyarrhythmias, but 16/32 cardiomyopathic turkeys (p less than 0.005) had inducible ventricular tachyarrhythmias, consisting most frequently of two beats of rapid ventricular tachycardia supervened by ventricular fibrillation. In the cardiomyopathic turkeys, inducible tachyarrhythmias occurred in 1/3 with normal dilatation index, in 11/25 with mild to moderate dilatation, and in 4/4 with severe dilatation. Thus, inducibility of ventricular tachyarrhythmias in cardiomyopathic turkeys is closely associated with increasing ventricular dilatation, but does not correlate with altered right ventricular refractoriness. This model may be suitable for studying the relationship between ventricular tachyarrhythmias and cardiomyopathy.