Pii: S1010-7940(00)00343-2

Objective: To test the hypothesis that mitral valve prosthesis±patient mismatch increases postoperative mortality. Methods and results: The effect of mitral valve prosthesis±patient mismatch on survival in a cohort of consecutive patients after mitral valve replacement with a mechanical prosthesis was measured, focusing on the lower tail of the normal distribution curve of the prosthetic valve area index. For the calculation of the geometric valve area index (cm/m body surface area), we used speci®cations for the geometric valve area supplied by the manufacturer. The cut-off value of the 10th percentile of the valve area index was 1.919 cm/m. The study population consisted of 428 adult patients who underwent mitral valve replacement by a Medtronic Hall (n ˆ 270, 63%) or a St. Jude Medical prosthesis (n ˆ 158, 37%). The size of the valves implanted ranged from 25 mm to 31 mm. The valve area index showed a normal distribution curve ranging from 1.43 to 2.98 cm/m with a mean of 2.2 cm/m. Group 1 (n ˆ 33) had a valve area index , 1:9 cm/m and group 2 (n ˆ 395), $ 1:9 cm/m. The 30-day mortality was higher in group 1 than in group 2 (18.2 vs. 4.1%, P ˆ 0:005). Multivariate logistic regression analysis of the determinants of the 30-day mortality rendered a small valve area index (, 1:9 cm/m) as an independent risk indicator: relative risk 4.3 (95% CI 1.6±9.5; P ˆ 0:0043). The difference in overall survival between the two groups was entirely due to the high 30-day mortality in the patients with small valve area indices, congestive heart failure being the main cause of death. Conclusions: By concentrating on the extreme lower tail of the normal distribution of the valve area index, a strong and independent relation was found between relatively small valves (valve area index , 1:9 cm/m) and 30-day mortality. We found no in ̄uence of valve size on late mortality beyond the ®rst 30 days. q 2000 Elsevier Science B.V. All rights reserved.