Among patients having intact retrograde atrial-ventricular (AV) conduction, PVC or other ventricular events may cause retrograde atrial depolarizations that occur during the postventricular atrial refractory period (PVARP). These atrial depolarization events do not initiate a new AV interval but may render subsequent atrial pacing stimulus ineffectual (i.e., if provided during the physiologic refractory period of the atria). In older cardiac pacing regimens, this phenomenon was dealt with under the general rubric of pacemaker syndrome.
Currently, most cardiac pacing systems have automatic atrial tachyarrhythmia (AT) recognition. Shortly after AT detection such cardiac pacing systems change the operating mode (i.e., perform mode-switching) for example by performing so-called anti-tachycardia “overdrive” pacing (ATP) to halt the AT.
Various methods to safely restore AV synchrony following non-physiologic atrial events (e.g., retrograde p-waves) have been known and used in the art. One approach is to deliver an atrial pace stimulus following a fixed delay (e.g., 300 ms) to allow the refractory myocardial tissue to recover and thereby reduce the risk of provoking an AT by competitive atrial pacing. One pacemaker manufacturer refers to their technique as non-competitive atrial pacing (NCAP), another refers to their technique as atrial synchronization pacing (ASP). The NCAP approach may be adapted to avoid repetitive AVDA sequences by simply extending the NCAP delay following a refractory event (e.g., event deemed non-physiologic). Such an extended delay allows additional time for the excitable atrial myocardial tissue to fully recover. However, the downside to this approach is a significant disruption of the paced rhythm, especially during sensor-driven pacing.
Other intervals timed by a pacemaker or implantable pulse generator (IPG) include atrial and ventricular sense amplifier blanking periods following delivery of atrial and/or ventricular pacing pulses to disable atrial and ventricular amplifier sensing. In addition, sense amplifier refractory periods are timed- or switched-out following atrial and ventricular paced and sensed event signals. Such “refractory” A-sense and V-sense signals are selectively ignored or employed in a variety of ways; for example, to reset or extend time periods or to gather evidence that an arrhythmia is present, and the like. An atrial refractory period (ARP) extends for various time durations through the Sensed AV (SAV) delay or the Paced AV (PAV) delay.
In addition, a post-ventricular atrial refractory period (PVARP) begins at a V-PACE pulse or V-SENSE event. A-SENSE signals occurring during the PVARP are noted (e.g., counted as evidence that an arrhythmia is present) but do not start an AV interval. The rationale for this operation is that such events may be a retrograde atrial sensed (AR) event or an event that is part of an atrial tachycardia episode. In either case, it is not desirable to synchronize ventricular pacing to such events. The duration of the PVARP may be fixed by programming, extended after a PVC, or vary as a function of the pacing or heart rate, with the result that in many cases relatively long PVARPs are in effect at lower rates.