Undersensing of P Waves in the Presence of an Adequate P Wave Due to Automatic Postventricular Atrial Refractory Period Extension

Abstract

Two cases in which a DDD pacemaker failed to track P waves due to repetitive activation of the automatic postventricular atrial refractory period (PVARP) extension are reported. In one case, the cycle was initiated by a premature ventricular contraction (PVC); in the other, by touching the unipolar pacemaker with a needle while suturing. We demonstrated that chest wall stimulation can be used to induce cycles of repetitive automatic PVARP extension and failure to track P waves. We demonstrated in vitro that touching a unipolar pacemaker with a needle can generate a signal sufficient to mimic a QRS complex, and initiate a cycle of repetitive P wave undersensing.

Pacemaker Syndrome Induced by the Mode Switching Algorithm of a DDDR Pacemaker

“…Such a situation may be considered in terms of a pacemaker syndrome with the pacemaker itself as a bystander once it has initiated the process. In some contemporary pacemakers and older Medtronic models, automatic PVARP extension after a pacemaker-defined VPC can cause the same disturhance as in our patient, if the pacemaker interprets the conducted QRS complexes as VPC when P waves continually fall in an automatically extended PVARP.^-^ However, VPC induced automatic PVARP extension was not the cause of the prohlem in our patient for two reasons: (1) The abnormality persisted when the VPC response was programmed off; and [2) In this pacemaker an atrial signal (AK) detected in the PVARP beyond the JAIS, ET AL. blanking period inhibits the VPC response.…”

Pacemaker Limitation of Tachycardia in Hypovolemic

“…Additionally, the newest generation of dual mode, dual chamber, and dual sensing pacemakers can often distinguish retrograde vs antegrade conduction of P waves, allowing for physiologic tachycardias to be sustained and nonphysiologic (retrograde P waves) terminated. 4,5 This patient, usually hypertensive, was in incipient hypovolemic shock. The heart rate of 58 was likely a factor in his initial limited responses and poor perfusion.…”

Programming a Long Paced Atrioventricular Interval May Be Risky in DDDR Pacing

“…This resulted in frequent T wave pacing with paced AV intervals of 200 msec [programmed; Figs. [3][4][5][6]. If the intrinsic R wave occurs within 110 msec of an 400 msec Figure 1.…”

“…The risk of these prohlems can be reduced by enlarging the atrial sensing window by programming shorter PVARPs (if possible) and sborter paced AV intervals. 4. In dual chamber pacemakers with ventricular-based timing, a situation can arise in which a QRS complex occurring after an atrial pace output resets the ventricular escape interval and can unexpectedly give rise to a pacemaker related tachy-cardia in which the atrial paced rate is higher than the programmed (or sensor driven) lower rate.^" In the Elite II pacemaker this is no longer possible because the timing of the V-A escape interval is only started after the programmed AV interval has heen timed out/ thus preventing premature resetting ofthe V-A escape interval hy a sensed ventricular event.…”

“…illustrates T wave pacing without ventricular capture at tbe onset of exercise after occurrence of the VPB as shown in Figures 1 and 2.Near the end of the exercise test the refractory period of the ventricular myocardium had shortened sufficiently to enable capture of tbe ventricle with a paced AV interval of 200 msec [Figs [4][5][6]…”