repetitive nonreentrant ventriculoatrial synchrony

Tracing
N° 31
Manufacturer Abbott Device PM Field AV delays, refractory periods management of tachycardia
Patient

71-year-old man, implanted with an AssurityTM + DR dual-chamber pacemaker for paroxysmal syncopal complete atrioventricular block; during the interrogation, highlighting of an AT/AF episode stored in the device memory.

Graph and trace

The tracing begins with AP-VP cycles with effective atrial and ventricular pacing at the sensor rate (SIR, rate modulation); a premature ventricular contraction is followed by retrograde conduction and sensing of atrial activity in the PVARP (AR); the following atrial pacing is ineffective since occurring in the refractory period following the preceding atrial depolarization; the cycle is repeated with retrograde conduction in PVARP and ineffective atrial pacing favoring retrograde conduction; the filtered atrial rate is calculated based on the intrinsic (AR or AS) but also paced (AP) cycles, which explains the recording of an episode diagnosed as AT/AF.

Comments

This tracing illustrates a particular and often underdiagnosed form of repetitive loss of atrial capture. Sensing of retrograde conduction occurs in the PVARP (functional undersensing) and is responsible for inefficient atrial pacing (loss of functional capture) since delivered in the physiological refractory period. This patient presented a normal atrial pacing threshold (<1V for 0.5 ms) with a suitable programming margin (2.5Volts for 0.5 ms). A repetitive nonreentrant ventriculoatrial synchrony begins when a premature ventricular contraction is followed by a retrograde atrial conduction that falls within the PVARP. The ensuing atrial pacing is ineffective since falling within the physiological atrial refractory period (loss of functional capture). At the end of the AV delay, ventricular pacing is delivered and is followed by retrograde conduction triggering repetitive retrograde atrial conduction, inefficient atrial pacing and ventricular pacing cycles. This is not a reentry (unlike a PMT), since retrograde atrial activity does not trigger ventricular pacing.

This type of repetitive sequences is preferentially diagnosed on the AbbottTM pacemakers by the peculiarity of their fallback algorithm function (the only one to integrate the AP cycles in the computation of the filtered atrial rate) which leads to the recording of an AT/AF episode. This type of problem is therefore underdiagnosed by other manufacturers although likely not less frequent.

For this type of repetitive sequences to begin, 2 elements must be unavailable: 1) a dual- or triple-chamber pacemaker programmed in DDD, DDDR, DDI or DDIR mode but not for the VDD mode since atrial pacing is required (difference with a PMT which is not possible with a DDI mode but possible with a VDD mode); 2) the presence of retrograde conduction.

Certain programming elements can also favor its occurrence: 1) high pacing rate (more common when the rate response or an atrial overdrive algorithm is programmed), the AR-AP interval being reduced (greater probability of atrial pacing being ineffective); 2) programming a long AV delay (favors retrograde conduction); 3) programming of a prolonged PVARP.

This type of repetitive sequence can induce a pacemaker syndrome, unnecessarily increase the percentage of ventricular pacing, is a cause of false diagnosis of atrial arrhythmia and can be arrhythmogenic (possible induction of a true AF episode).
To avoid this type of problem, different programming options can be considered: 1) lowering the minimum rate if the latter is high; 2) deprogramming rate response modulation if not absolutely essential; indeed, atrial pacing occurs much earlier relative to retrograde activation if rate modulation is programmed which increases the risk of loss of functional capture; 3) decreasing the value of the AV delay; 4) shortening the PVARP.

Message to remember

This type of repetitive sequence is often underdiagnosed and can lead to the occurrence of pacemaker syndrome. AbbottTM pacemakers are the only pacemakers that allow their recording in the form of false AT/AF episodes in the device memory.