This 83-year-old man underwent implantation of an Adapta dual chamber pacemaker for complete AV block; 4 days after his discharge from the hospital, he was seen in the emergency department, complaining of palpitations; this tracing was recorded; pacemaker is programmed to the DDDR mode.
Tracing 5a: recording upon the patient’s arrival; the first channel is lead I of the surface ECG upon which the markers are superimposed, the second channel shows the atrial EGM and the last channel is lead II with the time intervals superimposed;
Tracing 5b: an initial interrogation reveals that the anti PMT algorithm is OFF (nominal programming); the algorithm was programmed and the EGM recorded;
This tracing corresponds to an episode of PMT and highlights some aspects of the Medtronic dual chamber pacemakers function:
1) the algorithm for PMT interruption is not nominal programming; it must, therefore, be programmed on routinely, even in presence of AV block. It is indeed possible, as in this case, that anterograde conduction be interrupted and retrograde conduction preserved. It is also possible that it is absent at rest and present during exercise;
2) the interruption algorithm allows the distinction of sinus tachycardia from atrial tachycardia and PMT. Interruption of the tachycardia is highly in favor of PMT and, in this case, excludes sinus or atrial tachycardia. One needs to block retrograde conduction (VP-AS) only once or the AS-VP sequence to interrupt the tachycardia. The algorithm lengthens the refractory period, atrial retrograde activity no longer initiates an AV delay or a paced ventricular event and the tachycardia is interrupted;
3) in this sedentary 83-year-old patient, the PVARP can be programmed to 360 ms, i.e. longer than the retrograde conduction time. The programming of an AV delay that is relatively short and adaptive to exercise (paced AV delay of 140 ms during exercise) allows the setting of a 2:1 point at 120 bpm.
The programming of anti-PMT interventions is useful only when the retrograde conduction time is <400 ms and, therefore, does not intervene when it is > 400 ms. In such case, PMT remains incessant and the patient’s management is particularly challenging. Strong efforts must be made to avoid all situations that might facilitate the onset of PMT. A possible remedy might be the prescription of a drug that blocks retrograde conduction, which is already slowed, though this measure is rarely effective. Ablation by radiofrequency is another option, though this need is very rare.
