The ECG actually shows two things. The first is that from the ECG we can note atrial non -capture. The second part of the ECG shows atrial and ventricular pacing switching to atrial pacing only with no ventricular pacing and looks unusual but is actually ‘normal’ behaviour from the MVP algorithm in the Medtronic ADDAPTA DR (ADDR01) pacemaker. MVP or Manage Ventricular Pacing is an algorithm designed to reduce unnecessary ventricular pacing. It works by keeping the mode of the pacemaker in an atrial pacing mode which will switch to a dual pacemaker mode in the event of a non conducted atrial event (AAI to DDD) ie it must see a ventricular sensed event before another atrial sensed or paced event. In the ECG shown although the atrial lead is not capturing there is an R wave between each atrial pacing spike satisfying the MVP algorithm.
This was probably not the cause of the patients collapse as the patient had sufficient intrinsic rhythm and the ECG showing atrial non capture and MVP behaviour was really an incidental finding but does make for an interesting ECG and a bit of head scratching!