Refractoriness as a determinant of tachycardia inducibility in the right ventricle

Abstract

Listen

Translate article

The use of more than one right ventricular site for programmed electrical stimulation has been reported to increase the number of patients in whom ventricular tachycardia can be provoked. To determine a possible reason for these observations, programmed ventricular tachycardia studies were evaluated in 316 patients (185 men and 131 women) with a mean age of 63 ± 7 years who presented with ventricular tachycardia or cardiac arrest. The underlying cardiac disease was atherosclerosis (81%), cardiomyopathy (15%), valvular heart disease (3%), and miscellaneous conditions (1%). Programmed electrical stimulation studies employed a six-beat pacing train, at a cycle length of 500 msec with the introduction of one to three premature stimuli at twice diastolic threshold at the right ventricular apex. If ventricular tachycardia at the right ventricular apex could not be provoked in a patient, the study was repeated at the right ventricular outflow tract. A total of 36 patients were studied at the right ventricular outflow tract. Eleven (31%) were provoked into ventricular tachycardia, while 25 (69%) were not. No difference existed between the QRS, QT, and QT c intervals between those having ventricular tachycardia provoked at the outflow tract compared to those without inducible tachycardia at the right ventricular outflow tract. The effective refractory period was 280 ± 5 msec at the right ventricular outflow tract in those patients not inducible, and 226 ± 4 msec in those inducible ( p < 0.05). We defined the change in ventricular refractory period as the difference in the effective refractory period at the right ventricular outflow tract minus the effective refractory period at the right ventricular apex. The change in effective refractory period was −16 ± 2 msec for the 11 inducible patients and 8 ± 3 msec for the noninducible group ( p < 0.01). Thus, patients who are inducible for ventricular tachycardia at programmed ventricular stimulation at the right ventricular outflow tract have a shorter effective refractory period, and the difference in effective refractory period compared to the apex in the inducible group is also shorter. The earlier introduction of premature stimuli at the right ventricular outflow tract may permit a critically timed stimulus to initiate ventricular tachycardia.