Background: Cardiac resynchronization therapy (CRT) has proved as an efficient treatment in patients with end stage Heart failure. Previous studies showed the beneficial long term effects of CRT on the severity of mitral regurgitation (MR). The aim of this study was to evaluate acute effects of CRT on severity of MR.

Methods: This study was a double blind randomized trial performed from 1387 to 1388 in Imam Khomeini Hospital. Echocardiographic parameters including severity of MR were measured before and after CRT implantation with different echocardiographic methods.

Results: Patients had a significant improvement in severity of MR (14% Vs. 11% P<0/05), in increasing ejection fraction (18/04 Vs. 24/42 P<0/05) and in decreasing end systolic diameters (6/14 Vs. 5/98 P<0/05) and end diastolic diameters (7 Vs. 6/8 P<0/05) after CRT implantation. The reduction of MR was significantly correlated with the improvement of ejection fraction (P=0.07).

Conclusion: The mechanism of decreasing severity of MR is not yet truly understood and may be different in acute and chronic phases. Correction of left ventricular dyssynchrony might influence the improvement of MR severity. Also, synchronization of papillary muscle and increased transmitral pressure with more forceful mitral valve closure, decreases regurgitation fraction and volumes is proposed for these beneficial effects. If posterior papillary muscle is involved in dyssynchrony, the acute reduction of MR following CRT is expected but if the dyssynchrony is mainly at the lateral parts of left ventricle MR might be improved in longer durations.