This 77-year-old male recipient of Adapta dual chamber pacemaker implanted for complete AV block was seen for a routine evaluation.
Tracing 4a: the first channel is lead II of the surface ECG with the markers superimposed, the second shows the atrial EGM and the last channel is lead I with the time intervals superimposed;
Tracing 4b: atrial sensing is initially programmed at 0.5 mV; optimization to the highest sensitivity of the device;
Runaway ventricular pacing observed during rapid atrial rhythm can only occur when the atrial EGMs are sensed. In presence of an atrial arrhythmia that is consistently poorly sensed and associated with complete AV block, the pacing mode is DVI-like, with AV pacing at the backup rate or at the on-going sensor-driven rate. Atrial pacing is unnecessary and wastes energy. Furthermore, the device cannot memorize the episode, which, consequently, might be missed if the patient is asymptomatic. When the atrial signals are intermittently sensed, the ventricular rhythm becomes erratic. In this patient, an increase in atrial sensitivity enables a precise diagnosis of the arrhythmia with switch of DDD toward DDIR mode.
In Medtronic pacemakers, rate responsiveness is systematically programmed during mode switch, including when the initial mode is not sensor-driven. This seems appropriate for this patient who is in complete AV block and incapable of chronotropic adaptation during AF.
