Pacemaker-mediated tachycardia

ECG 10A: This is the same tachycardia as in the previous tracing (PMT); it stops on one cycle and restarts on the ensuing cycle;

ECG 10B: Analysis of the EGM allows establishing the diagnosis; initially, there is a PMT; programming of the anti-PMT algorithm (“programming successful”); diagnosis of PMT made by the device after 8 consecutive VP-AS cycles; intervention of the anti-PMT algorithm with a prolongation of the post-ventricular atrial refractory period (PVARP) to 400 ms on one cycle; atrial activity is sensed in PVARP (AR) and does not synchronize ventricular pacing; the following atrial pacing is ineffective favoring a retrograde conduction and the tachycardia restarts;

ECG 10C: This tracing shows the interruption of the PMT after programming of the anti-PMT algorithm and an increase in the amplitude of atrial pacing (correction of the triggering factor);

ECG 10D: EGM tracing showing the PMT interruption;

Comments: These 2 tracings correspond to PMT episodes and allow emphasizing certain elements of the functioning of dual-chamber pacemakers; 1) the anti-PMT algorithm is not switched on by default in Medtronic pacemakers; it is thus necessary to anticipate its programming even if the patient is in atrioventricular block. As in this patient, it is possible that the anterograde conduction is blocked but that retrograde conduction is preserved. It may also be absent at rest but present during exercise; 2) the anti-PMT algorithm allows differentiating sinus tachycardia, atrial tachycardia and PMT. Interruption of the tachycardia is strongly suggestive of a PMT and eliminates the hypothesis of sinus tachycardia or atrial tachycardia. The retrograde conduction (VP-AS) or the AS-VP sequence only needs to be blocked once to interrupt the tachycardia. The algorithm prolongs the refractory period, upon which the retrograde atrial activity no longer triggers the AV delay or ventricular pacing and the tachycardia is interrupted; 3) in this relatively inactive 79-year-old patient, it is possible to program a PVARP of 360 ms (the parameter designed to avoid sensing of retrograde atrial conduction), longer than the retrograde conduction time. Programming of a relatively short AV delay adaptable to exercise (AV delay sensed on exertion of 80 ms) allows ensuring a 2:1 point greater than 130 beats per minute.

These tracings also allow emphasizing an essential element of PMT management.  While it remains very important to program the interruption algorithm of these PMTs, it is also imperative to correct the initiating factor. The best treatment for PMT is prevention. Any event that promotes a loss of atrioventricular synchronism can generate PMT in patients whose retrograde conduction is preserved. In this patient, the originating problem was the loss of atrial capture. An increase in the amplitude of atrial pacing with a sufficient margin allowed resolving this issue.

Take-home message: PMT management involves the programming of a specific interruption algorithm, the programming of a PVARP longer than the retrograde conduction time (sometimes difficult because limiting in terms of monitoring atrial activity 1/1 during exercise), the prevention of episodes by suppressing triggering factors (pacing or sensing defects, oversensing, etc.).