The effects of cardioversion and defibrillation on left ventricular systolic function

The purpose of this research was to evaluate the left ventricular systolic function behavior after cardioversion and defibrillation. The study included 18 adult patients who had direct current cardioversion or defibrillation performed for conversion of spontaneous or induced arrhythmias. All patients were submitted to a careful medical evaluation and an M-mode echocardiogram before cardioversion or defibrillation. The clinical and echocardiographic evaluations were repeated immediately after, and 6 and 12 h following the countershock. Six hours after cardioversion or defibrillation a statistically significant (p = .04) decrease in contractility (circumferential fiber shortening and ejection fraction) was observed without significant changes in preload (end diastolic volume), heart rate or afterload (end systolic stress and diastolic arterial pressure). Within 12 h, the left ventricular systolic dysfunction disappeared. The impairment of systolic function was independent of the amount of energy used, the type of arrhythmia, the rhythm after cardioversion or defibrillation and the etiologic cardiac diagnoses. There was a significant (p = .03) direct, negative and linear correlation between left ventricular systolic indices (ejection fraction and circumferential fiber shortening) before the countershock and the amount of decrease in systolic function after the countershock. In spite of the fact that most patients had a low ejection fraction, none of them presented clinical signs of heart failure. Defibrillation and cardioversion produce a transient decrease in cardiac contractility which is independent of the amount of energy used and does not produce clinical signs of heart failure.