Tachycardia Mediated by an AV Universal (DDD) Pacemaker Triggered by a Ventricular Depolarization

Abstract

A 44-year-old female had Chagas' disease with right bundle branch block, right axis deviation, and ventricular ectopic beats. An invasive evaluation showed a prolonged HV interval of 100 ms. A Medtronic Versatrax 7000 was implanted, after which a pacemaker-mediated tachycardia was observed. The esophageal lead ruled out the possibility of an atrial triggered tachycardia. The diagnosis was pacemaker-mediated tachycardia due to abnormal sensing of the terminal forces of the ventricular activation because of malposition of the atrial lead in the right ventricular out-flow tract.

Ventricular Activation Sequence during Left Ventricular Pacing Promotes QRS Complex Oversensing in the Atrial Channel

“…QRS oversensing is not likely to occur in the atrial channel during classic, DDD‐RV pacing with standard PVARP values (250 ms), since RV depolarization does not last >200 ms. Moreover, in all patients described to date, far‐field ELT resulting from QRS oversensing was due either to short PVARP (150–200 ms) 3,4 or was not confirmed by intracardiac electrograms and, therefore, likely represented T wave rather than QRS oversensing 5 …”

Terminology of Pacemaker Reentrant Tachycardias

“…1), the sensing lead detects signals originating from a chamber different from the one where the lead is located (Table II). 3 The term pacemaker mediated tachycardia (PMT) is often used interchangeably with ELT, but it is too broad. PMT simply means that a tachycardia requires continued active participation of the pacemaker for its maintenance.…”

“…The mechanism is as in (1) except that the atrial channel of the pacemaker senses part of ventricular depolarization rather than retrograde P waves. (3) Orthodromic dual chamber (near-field) pacemaker tachycardia. The pacemaker delivers an atrial stimulus whenever the ventricular channel senses a signal interpreted as a ventricular extrasystole (synchronous atrial stimulation).…”