Functional Mitral Regurgitation at Rest Determines the Acute Hemodynamic Response to Cardiac Resynchronization Therapy During Exercise: An Acute Exercise Echocardiographic Study

Background: Cardiac resynchronization therapy (CRT) acutely enhances forward stroke volume (FSV) during exercise by reducing the severity of functional mitral regurgitation (MR) in patients with systolic chronic heart failure. Whether CRT increases FSV in patients without functional MR at rest is unknown. Accordingly, the aim of the study was to compare the effect of CRT on exercise-induced increase in FSV in patients with chronic heart failure with or without functional MR at rest. Methods and Results: Forty-one patients with systolic chronic heart failure who had recently undergone CRT performed 2 exercise stress echocardiography tests, the first with CRT On and the second with CRT Off. Twenty-six patients had more than trivial MR (effective regurgitant orifice [ERO] < 10 mm(2) in 16 patients, < 20 mm(2) in 8 patients, and >= 20 mm(2) in 2 patients), and 15 patients had no MR at rest. Mean exercise-induced change (Delta) in mitral ERO was reduced by CRT (8 +/- 7 mm(2) vs 1 +/- 4 mm(2), P<.00001). In patients with functional MR at rest, Delta FSV during dynamic exercise was greater with CRT On than CRT Off (4 +/- 8 vs -2 +/- 7 mL, P=.0002), whereas CRT did not significantly affect Delta FSV in patients without MR at rest (9 +/- 9 mL vs 9 +/- 9 mL, P=.93). Similarly, Delta cardiac output was greater with CRT On than CRT Off (1.6 +/- 1.2 L/min vs 1.1 +/- 1.2 L/min, P=.002) in patients with functional MR at rest, whereas Delta cardiac output was similar with CRT On and CRT Off in patients without MR at rest (1.9 +/- 1.4 L/min vs 2.0 +/- 1.2 L/min, P=.59). Severity of functional MR decreased or failed to increase, whereas cardiac output improved during exercise in 9 of 26 patients (34%) with CRT On and in only 2 of 26 patients (8%) with CRT Off (P=.039). Conclusion: Functional MR at rest may be an important determinant of the acute hemodynamic response to CRT during exercise. (J Am Soc Echocardiogr 2009; 22: 464-471.)