Significant prolongation of atrial monophasic action potential duration: short-term reverse electrophysiological changes after internal cardioversion of atrial fibrillation.

OBJECTIVE Since short action potentials and short refractory periods facilitate the induction of atrial reentry, this maladaptation has been proposed as the pathophysiological basis of the frequent immediate recurrences of atrial fibrillation (IRAF) after internal cardioversion. However, short-term reverse electrophysiological changes of the atria after cardioversion have not been studied in humans. METHODS Thirty-seven patients with chronic atrial fibrillation of 16+/-19 months and ten patients with an atrial fibrillation duration < or =48 h underwent internal cardioversion. Antiarrhythmic medication was only continued in 10 patients (21%), who were on amiodarone before cardioversion. Atrial monophasic action potential duration at 90% repolarization (APD(90)), sinus rate, P wave duration and interatrial conduction times between high right atrium and coronary sinus were recorded at min 0, 1, 3, 5, 10, 15 and 20 after cardioversion. RESULTS Internal cardioversion was successful in all patients, but twelve of the patients with chronic AF (32%) and three of the patients with intermittent AF (30%) had one to four episodes of IRAF after 16+/-28 s. There was a significant 52+/-30 ms APD(90) prolongation, 83% of which occurred in min 0-3 (P<0.0001) and 17% in min 3-20 (P<0.05) after internal cardioversion. There was no significant temporal change in sinus rate, P-wave and interatrial conduction time during the time studied. APD(90) prolongation and its time dependence did not show a detectable difference in subgroups with chronic AF, IRAF, left atrial size >40 mm and treatment with amiodarone. CONCLUSIONS There is a significant prolongation of action potential duration in min 0-3 after internal cardioversion of atrial fibrillation, whereas sinus rate and intra- and interatrial conduction time remain unchanged. APD(90) prolongation in min 0-3 shows a temporal relationship to the high rate of immediate recurrences of atrial fibrillation during this time interval. The data imply that there is a transient recovery of atrial refractoriness after cardioversion and suggest a mechanism of the high rate of early recurrences of atrial fibrillation.