Dispersion of 'refractoriness' in noninfarcted myocardium of patients with ventricular tachycardia or ventricular fibrillation after myocardial infarction.

Abstract

Postinfarction ventricular tachycardias (VTs) may degenerate into ventricular fibrillation (VF), but this does not happen in all patients. The underlying mechanism is not exactly known, but dispersion of refractory periods is considered a major factor in both induction and persistence of reentrant arrhythmias in general. Hypertrophied, noninfarcted myocardium has altered electrophysiological characteristics. We hypothesized that noninfarcted ventricular tissue may provide the heterogeneities that cause the transition from VT into VF. Local fibrillation intervals, ie, the average interval between local activations during VF, have previously been shown to correlate well with local refractoriness in human and canine atrium and in porcine and canine ventricle and may therefore be used as an index of local refractoriness. This technique permits simultaneous assessment of refractoriness at multiple sites. We measured local fibrillation intervals at 32 to 64 sites in the noninfarcted part of the left ventricle in patients undergoing antiarrhythmic surgery for symptomatic, drug-refractory, postinfarction ventricular tachyarrhythmias. The grid of electrodes (interelectrode distance, 7 mm) was attached to the epicardium of the left ventricle remote from the infarcted tissue. Group 1 consisted of 7 patients with hemodynamically tolerable sustained VT (VT group). Group 2 consisted of 7 patients with cardiac arrest and documented VF (VF group). With the patients on cardiopulmonary bypass, VF was induced by multiple premature stimulation. The VF interval was not significantly different in the two study groups (VT group, 136 +/- 5.5 ms; VF group, 129 +/- 3.4 ms, mean +/- SEM). However, spatial dispersion of the VF intervals (remote from the infarcted area) expressed as the coefficient of variation of VF intervals (SD x 100/mean VF interval in each heart) was significantly larger in the VF group. It was 3.63 +/- 0.56 in the VF group and 1.55 +/- 0.40 in the VT group (mean +/- SEM; P < .01). Differences between the shortest and longest VF intervals in one and the same heart and the largest difference between two adjacent sites were also larger in the VF group (P < .02 and P < .05, respectively). This study shows larger dispersion in VF intervals and therefore suggests larger dispersion of refractory periods in parts of the myocardium remote from the infarction in patients with postinfarction VF than in patients with postinfarction VT.