Dispersion of Refractoriness in Ventricular Tachycardia Induction from the Right Ventricle

Abstract

To determine whether dispersion of ventricular refractoriness plays a role in ventricular tachycardia induction from the right ventricle, we measured effective and functional refractory period at the apex and outflow tract. Induction was attempted at both sites using two train cycle lengths and up to two extrastimuli. Twenty‐two patients with remote myocardial infarction and documented ventricular tachycardia or sudden death were studied. Fourteen (group IA) had tachycardia inducible using this protocol; eight (group IB) did not. Dispersion defined as the absolute difference between the two sites was significantly greater in group IA than in group IB for functional refractoriness (e.g., 22 ± 21 msec vs 9 ± 11 msec at a cycle length of 600 msec), whereas dispersion of ventricular effective refractory period was not. A dispersion of 20 msec or greater had a positive predictive value of 90% for tachycardia induction. These results were compared to two control groups: group II (13 patients) with remote infarction but neither documented nor inducible ventricular tachycardia and group III (19 patients) without infarction or ventricular tachycardia. Dispersion of refractoriness in these two groups was similar to that in group IB.With the study protocol, ventricular tachycardia was inducible at the apex only in eight cases and at the outflow tract only in five. Functional refractory period was 17 ± 30 msec shorter at the site of induction. The site of shortest functional refractory period and the site of induction were, however, identical in only 8/13 cases (62%), but in these eight, the coupling intervals necessary for induction were attainable only at the induction site. This indicates at least a moderate role for local properties of refractoriness in determining the site of successful induction.