CARDIAC-PERFORMANCE EARLY AFTER CARDIOVERSION FROM ATRIAL-FIBRILLATION

Background The mechanism for early improvement in cardiac function aft er cardioversion from atrial fibrillation is unknown. Methods We measu red ventricular volumes and load-independent contractility during atri al fibrillation and within 24 hours after cardioversion to sinus rhyth m in 15 adult patients (10 men, 5 women; mean age 63 +/- 4 years, rang e 31 to 81 years). Duration of atrial fibrillation ranged from <1 day to 6 months. Results After cardioversion, left ventricular ejection fr action increased from 51% +/- 4% to 61 % + 4% (P = .001, 95% confidenc e intervals for the difference, 7% to 15%), stroke volume increased fr om 57 +/- 4 mL to 76 +/- 6 mL (P <.001, 95% confidence intervals 8 to 32 mi), and mean cycle length increased from 0.77 +/- .04 seconds in a trial fibrillation to 1.02 +/- .04 seconds in sinus rhythm (P = .002, 95% confidence intervals. 0.1 to 0.1 seconds). Cardiac contractility, as expressed by the slope and the intercept of the relation between ra te-corrected circumferential velocity of fiber shortening and end-syst olic wall stress (Vcfc/ESWS) remained unaltered in 13 of 15 patients, suggesting that intrinsic inotropic state was unchanged immediately af ter return of normal sinus rhythm. Finally, a significant correlation was observed between improvement in stroke volume and peak A-wave velo city (r = 0.79, P = .035). Conclusion Both left ventricular stroke vol ume and election fraction increase immediately after cardioversion, wh ereas intrinsic cardiac contractility is largely unchanged. These data suggest that the mechanism of this increase is enhanced left ventricu lar diastolic filling due mostly to increased cycle length and return of left atrial mechanical function.