Prosthesis–patient mismatch affects long-term survival after mechanical valve replacement

Abstract

We sought to examine the relationship between the degree of prosthesis-patient mismatch and long-term survival after mechanical aortic valve replacement. Prospectively collected long-term follow-up data from 469 consecutive patients who underwent aortic valve replacement between 1995 and 1998 were reviewed. The indexed effective orifice area was derived from the reference normal values of effective orifice area divided by the patient's body surface area. Outcome was stratified according to the severity of prosthesis-patient mismatch: moderate mismatch was defined as 0.65 to 0.85 cm(2)/m(2) and severe mismatch as less than 0.65 cm(2)/m(2). The Cox proportional-hazards model with propensity score adjustment was used to adjust for the observed differences in baseline characteristics between the mismatch groups. The degree of prosthesis-patient mismatch was minimal in 57% of patients, moderate in 39%, and severe in 4%. Predictors of clinically significant mismatch included small aortic valve sizes (19 and 21 mm), obesity, age greater than 65 years, and class III or IV heart failure. During a median follow-up period of approximately 7.9 years, overall survival was 77% in patients with minimal mismatch, 63% in those with moderate mismatch, and only 47% in those with severe mismatch (P < .001). Moderate or severe mismatch was a significant predictor of poorer survival (hazard ratio, 1.6; 95% confidence interval, 1.4-2.3; P < .01), even after adjustment for all significant clinical predictors (ie, propensity score; hazard ratio, 1.2; 95% confidence interval, 1.0-1.5; P = .05). In a large aortic valve surgery population, prosthesis-patient mismatch occurred in 43% of patients, and those with significant mismatch had worse long-term outcomes than those with minimal mismatch.