It has been demonstrated that atrial fibrillation (AF) induces shortening of atrial refractory period, which was known as electrical remodeling, resulting in an increased vulnerability for reinduction of AF. Atrial mechanical function does not restore immediately after cardioversion, atrial stunning exists during this period in chronic AF. We hypothesized that electrical remodeling in chronic AF determines the atrial mechanical dysfunction after cardioversion and early relapse of AF.

Patients with chronic atrial fibrillation (CAF, n=17) who have been done transthoracic DC cardioversion, paroxysmal AF (PAF, n=11), and normal control (CON, n=5) were studied. Using MAP (monophasic action potential) catheter, MAP duration 90% repolarizition (MAPD90) and atrial effective refractory period (AERP) were measured at 9 different sites in the right atrium. Magnitude of dispersion of these parameters was calculated by SD2 (variance). Assessment of mitral inflow variables (peak velosities of A, E wave, and A/E ratio) was performed at immediately after DC cardioversion, 1st day, 3rd days, 1 week, 4 weeks and 8 weeks by transthoracic pulse wave Doppler.

MA-PD90 significantly shortened in patients with CAF (235.4±38.1 ms) compared with that of PAF (270.9±45.2 ms) and control (274.0±51.9 ms), whereas AERP did not show significant differences. The magnitude of dispersion of MAPD90 and AERP was not different among the groups. AF recurred in 9 of 17 (53%) patients with CAF particularly in whom A/E ratio was <0.4 immediately after cardioversion (positive predictive value; 89%). MAPD90 (229.3±28.2 ms) in patients who recurred AF with small A/E ratio (<0.4) was shorter than that of maintained sinus rhythm with higher A/E ratio (>0.4)(250.9±52.9 ms, p=0.05).

Electrical remodeling in chronic human AF characterized by shortening of monophasic action potential duration is one of the main factors that determines the atrial mechanical dysfunction after cardioversion and early relapse into AF.