Inducible polymorphic ventricular tachycardia and ventricular fibrillation in a subgroup of patients with hypertrophic cardiomyopathy at high risk for sudden death.

This investigation was undertaken to elucidate the underlying electrophysiologic substrate in hypertrophic cardiomyopathy and to identify possible predictors of sudden death in this patient population. Programmed stimulation was performed in 18 patients aged 14 to 64 years (mean 36) believed to be at high risk for sudden death on the basis of prior cardiac arrest or syncope, nonsustained ventricular tachycardia on Holter ambulatory electrocardiographic (ECG) monitoring or a family history of frequent sudden death. Polymorphic ventricular tachycardia that deteriorated to ventricular fibrillation was reproducibly induced in 8 (44%) of the 18 patients (Group A). This rhythm was induced in all three patients with a history of cardiac arrest. No sustained monomorphic ventricular tachycardia was induced. Group B comprised the 10 patients in whom a sustained arrhythmia could not be reproducibly initiated. The electrophysiologic substrate was distinctly different in patients with, than in those without, inducible sustained arrhythmia. The refractory period was shorter at the right ventricular outflow tract (232 +/- 22 ms) compared with the apex (264 +/- 12 ms) in Group A (p less than 0.005) whereas there was no difference in Group B (271 +/- 25 ms versus 271 +/- 13 ms). The local ventricular electrogram of most patients in both groups was prolonged and markedly multiphasic. However, 5 of the 8 Group A patients exhibited a double electrogram (V-V') with premature stimulation compared with 1 of the 10 patients in Group B (p less than 0.02). A positive R wave in lead aVR of the scalar ECG and poor R wave progression in the precordial leads were more common in Group A than in Group B (p less than 0.001 and p less than 0.001, respectively). The reason for the distinctly different electrophysiologic substrate and the high prevalence of inducible polymorphic arrhythmia is unclear. It may relate to the underlying myocardial architecture in these patients, characterized by myocardial cellular disarray and fibrosis.