The Syndrome of Severe Mitral Regurgitation with Normal Left Atrial Pressure

It has been generally thought that significant elevations of the left atrial and pulmonary vascular pressures occur in patients with mitral regurgitation of sufficient severity to produce serious disability and gross enlargement of the left atrium. Ten patients with severe mitral regurgitation have been encountered in whom gross left atrial enlargement was accompanied by normal left atrial and pulmonary artery pressures. These patients ranged in age from 8 to 49 years, all were in functional classes III or IV, and the average duration of symptoms was 7.3 years. Nine patients had rheumatic mitral regurgitation while one had a congenital lesion. Atrial fibrillation and the physical findings of pure mitral regurgitation were present in all patients, as was striking left atrial enlargement on their roentgenograms. Left atrial pressure, determined by left heart catheterization, averaged 9.1 mm. Hg and did not exceed 12 mm. Hg in any patient, and the V wave was not particularly prominent. The cardiac index was markedly depressed and averaged 2.0 L./min./M. 2 B.S.A. The observed discrepancy between left atrial size and pressure must reflect a disturbance in the compliance of the left atrial wall. It is suggested that long-standing mitral regurgitation may modify the mechanical characteristics of the atrial wall and that the presence of a normal left atrial pressure must not be assumed to exclude the presence of severe mitral regurgitation. The manner in which variations in left atrial compliance affect the clinical picture of mitral regurgitation and the selection of patients for operative intervention are discussed.