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.
MVP with decrease in atrial pacing amplitude below the pacing threshold;
A proper function of the MVP mode requires accurate atrial and ventricular sensing and proper atrial and ventricular pacing. An abnormality of one of these elements results in dysfunction of the algorithm. In this patient, the pacemaker switches to DDD because of loss of atrial capture.
The setting of the refractory periods requires specific consideration. When the pacemaker operates in AAI mode, the atrial refractory period varies as a function of the ongoing heart rate, and corresponds to 75% of the cardiac cycle, though no longer than 600 ms. In this tracing, the spontaneous atrial events occurring less than 600 ms after atrial pacing (AP) are within the refractory period (AR). The spontaneous atrial events occurring >600 ms after atrial pacing (AP) are not within the refractory period (AS). In the AAI mode, blanking lasts 100 ms in the atrium after sensing or atrial pacing, 80 ms in the ventricle after atrial pacing, and 100 ms in the ventricle after sensing or ventricular pacing.
