Factors associated with operative risk in mitral valve replacement

Abstract

A retrospective analysis was made of 110 consecutive patients undergoing isolated mitral valve replacement with a ball valve prosthesis in an attempt to define factors associated with operative risk. Fourteen of the patients died after operation (operative mortality 12.7 per cent) and in 10 of these the primary cause of death was believed to be low cardiac output. With 1 exception, all patients who died with low output were considered to be in functional class iv and exhibited three or more of the following factors: (1) reduced cardiac index, (2) marked cardiomegaly, (3) atrial fibrillation, (4) pulmonary hypertension, (5) surgically uncorrected moderate aortic insufficiency, (6) a mixed stenotic-regurgitant lesion, and (7) a history of previous mitral valve surgery, especially in patients over the age of 55. Approximately one third of the patients with a preoperative cardiac index of 1.9 L./min./M. 2 or less died, as did one fourth of those with marked cardiomegaly. When both determinants were present almost half (6 of 13) failed to survive. The operative risk was low in patients with a cardiac index above 2.0 and in those having sinus rhythm. The nature of the risk was primarily technical rather than one of intrinsic myocardial dysfunction. Virtually five sixths of the patients (49 of 60) with pulmonary hypertension survived operation although this factor was present in 11 of 14 patients who died. When reduced cardiac index (1.9 L./min./M. 2 or less) coexisted with pulmonary hypertension one third of the patients died. Coexisting valvular disease uncorrected at operation had a varying influence on operative mortality. Patients with trivial degrees of aortic incompetence withstood surgery well although moderate incompetence was associated with increased surgical risk. On the other hand, the presence of significant functional tricuspid incompetence did not appear to influence the outcome adversely. Operative mortality was higher in patients who had undergone previous mitral valve surgery. These patients were also significantly older. Although no single determinant was found to represent a unique hallmark of operative risk which would constitute, per se, an overriding contraindication to mitral valve replacement, there was a direct relation between the cumulative number of determinants and operative mortality. Eighty-three of 87 patients with three determinants or fewer survived. Three of the 4 deaths in this group were of technical origin. On the other hand, mortality related to myocardial dysfunction was commonly observed in patients exhibiting four or more factors and included 8 of the 10 patients who died with low cardiac output. Precise operative conduct and meticulous myocardial support in the postoperative period will permit survival of the majority of patients with marginal cardiac reserve after mitral valve replacement even when multiple factors contributing to operative risk are present.