Small valve area index: its influence on early mortality after mitral valve replacement

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 (cm2/m2 body surface area), we used specifications 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 cm2/m2. The study population consisted of 428 adult patients who underwent mitral valve replacement by a Medtronic Hall (n=270, 63%) or a St. Jude Medical prosthesis (n=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 cm2/m2 with a mean of 2.2 cm2/m2. Group 1 (n=33) had a valve area index ≪1.9 cm2/m2 and group 2 (n=395), ≧1.9 cm2/m2. The 30-day mortality was higher in group 1 than in group 2 (18.2 vs. 4.1%, P=0.005). Multivariate logistic regression analysis of the determinants of the 30-day mortality rendered a small valve area index (≪1.9 cm2/m2) as an independent risk indicator: relative risk 4.3 (95% CI 1.6–9.5; P=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 cm2/m2) and 30-day mortality. We found no influence of valve size on late mortality beyond the first 30 days.