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.