Possible Mechanisms of RNRVAS development as a result of atrial capture problem
In this study we demonstrated that RNRVAS is triggered as a result of atrial capture failure. This may be due to the following situations:
1. A lower rate limit set to a high heart rate or sensor rate response result in atrial pacing at high heart rates. This increases atrial pacing rate with atrial capture loss and increases the probability of triggering RNRVAS.
2. During atrial threshold test in devices that automatically measure threshold periodically, loss of capture may trigger RNRVAS.
3. After an atrial ectopic beat, pace stimulus in atrium may fall in the myocardial refractory period causing non-capture and this may trigger RNRVAS.
After a non-captured atrial pace stimulus, the device waits during the AV delay duration and paces the ventricle. Because the atrium is not captured, the AV node is not refractory when ventricle is paced, so the signal is conducted retrogradely to the atrium. This retrograde atrial signal falls into PVARP, therefore it is sensed but doesn’t trigger AV delay. The device waits until the lower rate limit is reached and tries to pace the atrium but the atrium is in the refractory period or atrial threshold is high so it is not captured. This continues in a loop leading to RNRVAS which ends if VA conduction is somehow blocked or atrium is captured.