This 63-year-old man presented with a history of paroxysmal atrial fibrillation (AF) and complete right bundle branch block on the electrocardiogram (ECG). He suffered 3 episodes of syncope without prodrome. An electrophysiologic study revealed an 82-ms HV interval, prompting the implantation of an Adapta® dual chamber pacemaker. Both pacing leads were properly positioned and associated with normal impedance, and satisfactory sensing and capture thresholds. The pacemaker was interrogated 3 days after the implant and recordings were obtained during the programming of various pacing modes. This first tracing was recorded in ODO mode.
Tracing: DDD mode programmed at 60 bpm;
The fundamental principle of the DDD mode consists in synchronizing ventricular pacing with atrial sensing (triggered function) or pacing. A spontaneous atrial or ventricular event sensed outside the refractory period inhibits atrial or ventricular pacing (inhibited function). Consequently, this mode allows the preservation of atrial synchrony between low and high (upper rate limit) sinus rates. All atrial events sensed outside the refractory period between backup and maximum synchronous rate or atrial pacing initiates the AV delay with ventricular pacing in absence of spontaneous ventricular sensing.
Therefore, the programming of DDD mode seems appropriate for this patient. The follow-up would probably reveal nearly 100% ventricular pacing, i.e. apparently normal and desirable function. An analysis in ODO mode, however, revealed normal AV conduction.
One of the priorities, when programming a pacemaker, is to eliminate all unnecessary ventricular pacing, allowing a) the sparing of significant battery consumption and the prolongation of the pulse generator longevity, and b) above all, to limit right ventricular pacing, which, on the short, intermediate and long term, is associated with potential deleterious hemodynamic effects, as well as ventricular remodeling and development of atrial arrhythmias. Right ventricular pacing causes an asynchronous sequence of inter- and intraventricular activation and relaxation. A high percentage of ventricular paced events in a patient presenting with preserved AV conduction should be noted at the time of device interrogation and initiate implementation of specific ventricular pacing avoidance algorithms.
