Improved method for evaluating ventriculoatrial conduction before implantation of atrial-sensing dual chamber pacemakers

Pacemaker-mediated tachycardia may occur when a spontaneous ventricular premature depolarization is retrogradely conducted to the atrium with a ventriculoatrial (VA) interval that exceeds the atrial refractory period of an atrial-sensing dual chamber pacemaker. Previous methods for evaluating VA conduction have failed to predict clinical occurrences of pacemaker-mediated tachycardia. In this study, maximal VA intervals after ventricular extrastimuli during atrial or atrioventricular (AV) sequential pacing were compared with intervals measured by the standard method of ventricular pacing. VA intervals were 201 ± 53 ms during ventricular pacing and 224 ± 52 ms after ventricular extrastimuli during atrial pacing (p = NS). VA intervals were 305 ± 77 ms after ventricular extrastimuli during AV sequential pacing and were longer than VA intervals during ventricular pacing (p < 0.001) or after ventricular extrastimuli during atrial pacing (p < 0.01). Thus, the ventricular extrastimulus technique during AV sequential pacing reveals substantially longer VA intervals than does ventricular pacing and explains why pacemaker-mediated tachycardia might occur when pacemaker atrial refractory periods are designed or programmed according to VA intervals measured only during ventricular pacing.