Exercise-Induced Changes of Functional Mitral Regurgitation in Asymptomatic or Mildly Symptomatic Patients With Idiopathic Dilated Cardiomyopathy

It has remained unclear why functional mitral regurgitation (MR), even if it is of a mild degree, has prognostic importance in patients with idiopathic dilated cardiomyopathy (IDC). Exercise-induced changes in functional MR, which might be a clue to this question, have not been fully clarified. Thus, in this study, semisupine exercise echocardiography was performed on 32 asymptomatic or mildly symptomatic patients with IDC (29 men, mean age 45 ± 14 years). The mean ejection fraction was 28 ± 10% (range 13% to 45%). The effective regurgitant orifice (ERO) area of MR was measured, as well as echocardiographic parameters including mitral valve geometry. ERO at rest was associated best with systolic mitral tenting area (r_S = 0.85, p <0.001). Functional MR did not newly appear during exercise in 9 subjects without MR at rest. In the remaining 23 subjects with functional MR at rest, all showed exacerbations of MR, with a median ERO of 10.5 mm² (interquartile range 6.3 to 16.5) to 18.7 mm² (interquartile range 9.5 to 29.3) (p <0.001). An increase in ERO was correlated best with the enlargement of tenting area (r_S = 0.90, p <0.001) and was the strongest independent determinant of exercise duration (β = -0.55, p = 0.002, multiple R² = 0.46). In conclusion, functional MR complicated with IDC was significantly exacerbated during exercise, with mitral valve deformation, which was strongly related to exercise intolerance; thus, the clinical impact of functional MR in patients with IDC could be more serious than can be expected by its degree at rest.