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

To test the hypothesis that mitral valve prosthesis-patient mismatch increases postoperative mortality.

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(2)/m(2) 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 cm(2)/m(2). 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 cm(2)/m(2) with a mean of 2.2 cm(2)/m(2). Group 1 (n=33) had a valve area index <1.9 cm(2)/m(2) and group 2 (n=395), > or =1.9 cm(2)/m(2). 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 cm(2)/m(2)) 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.

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(2)/m(2)) and 30-day mortality. We found no influence of valve size on late mortality beyond the first 30 days.