This patient presented multiple episodes of PMT induced by a failure of atrial capture. A long AV delay was programmed to promote spontaneous conduction, which also increased the risk of initiating and maintaining a PMT. This tracing illustrates the specificity of the new anti-PMT algorithm available on the latest dual-chamber pacemaker platforms. This algorithm includes a confirmation phase with modification of the AV delay to affirm the diagnosis of PMT and to differentiate the latter from that of sinus tachycardia. After 8 consecutive VP-AS intervals, the AV delay is prolonged by 50 ms over one cycle; the VA interval is then measured as a result of this modification in AV delay over 2 consecutive intervals. If, despite this modification, the VA interval remains constant, a PMT is suspected (in the case of sinus tachycardia, atrial intervals are not altered by a change in AV delay; if the AV delay is prolonged over one interval, the VA interval is therefore shortened). This sequence is repeated 3 times (prolongation of the AV delay over one interval, followed by normal AV delay over 2 intervals). If analysis of the VA delays (VP-AS) is indicative of a PMT, the PVARP is prolonged to 400 ms over one interval for the next atrial event to be sensed in the refractory period. This refractory event is not synchronized to the ventricle during 1 interval and the tachycardia is terminated.

The objective of this new algorithm, with confirmation of the diagnosis of PMT before attempting to terminate the latter by prolonging the PVARP over one interval, is to increase the specificity and avoid inappropriate interventions during a sinus tachycardia which led to the occurrence of a blocked P wave which could be symptomatic and possibly arrhythmogenic during exertion.