Objectives .– We studied the effects of cardiac resynchronization therapy (CRT) on functional mitral regurgitation in heart failure (HF) patients.

Background .– Functional mitral regurgitation (FMR) is a common finding in patients with global left ventricular (LV) dilatation and dysfunction.

Several recent studies demonstrated that cardiac resynchronization therapy (CRT) might be able to reduce FMR.

Methods .– Twenty-nine patients with heart failure and FMR were studied after implantation of a biventricular CRT system. Clinical responders were predefined as survived patients with an improvement by one or more NYHA functional class.

Changes in FMR severity after CRT were quantified according to the proximal isovelocity surface area method by measuring the effective regurgitant orifice area (EROA) and the regurgitant volume (RV).

Results .– Twenty-nine patients (mean age, 66 ± 8 years; 26 men; mean LV ejection fraction 25 ± 7%) with severe HF were included. All patients were restudied at a mean of 8 ± 2 months after CRT; 26 (89%) were clinical responders.

Cardiac resynchronization therapy was associated with a significant reduction in FMR severity in clinical responders; effective regurgitant orifice area (EROA) decreased from 19 ± 18 mm ² to 8 ± 7 mm ² ( P < 0.001) and regurgitant volume (RV) decreased from 19 ± 11 mL/beat to 10 ± 9 mL/beat ( P < 0.001). This was accompanied by a significant reduction in LV volumes and an increase in ejection fraction ( P = 0.001).

In clinical nonresponders, there was not a significant decrease in MR severity; EROA decreased from 28 ± 6 mm ² to 22 ± 13 mm ² ( P = 0.18) and RV from 25 ± 5 mL/beat to 22 ± 8 mL/beat ( P = 0.18).

Conclusion .– Functional mitral regurgitation is reduced in clinical responders to CRT. Thus, FMR may be an important factor influencing clinical response to CRT.