Atrial Refractoriness and Action Potential Duration After Sudden Reversal of Atrioventricular Sequence

To address the potential of atrioventricular (AV) asynchrony to provoke cardiac arrhythmias, atrial electrophysiology was examined during normal and reversed AV interval in anesthetized pigs. A new automatic stimulation technique was adapted to monitor rapid changes in the effective refractory period (ERP), using continuous AV sequential pacing, incremental extrastimulus interval scanning, and automatic detection of capture. Right atrial ERP using 2-8 ms stimulus interval increments and right atrial and ventricular monophasic action potential (MAP) duration were determined simultaneously when the AV interval was changed from normal (+80 ms) to reversed (-40 ms) and back. During reversed AV interval the peak right atrial pressure increased from 8 +/- 3 to 14 +/- 4 mmHg (P < 0.001) and mean arterial pressure decreased from 86 +/- 18 to 65 +/- 21 mmHg (P < 0.001). At new steady state, atrial ERP and MAP duration at 90% level of repolarization were lengthened by 22 +/- 16 and 42 +/- 12 ms respectively (P < 0.001). Ventricular MAP duration did not change. A statistically significant lengthening in atrial ERP could be demonstrated in 5-10 seconds. After reversion of the AV sequence, the ratio of atrial ERP to MAP duration decreased from 1.27 to 0.94 (P < 0.001) on average for 15 seconds, the change being thought to favor reentry. Thus atrial wall stress from contraction during ventricular systole even for a short period of time modifies atrial electrophysiology. Deficient AV synchrony may immediately contribute to the development of atrial arrhythmias.