Echocardiographically derived effective valve opening area in mitral prostheses: a comparative analysis of various calculations using continuity equation and pressure half time method.

ABSTRACT

Detection of dysfunctional mitral valve prostheses (MP) remains complex even though being optimized by considering echocardiographically derived prosthetic effective orifice area (VA). The purpose was to compare VA in MP, calculated by the continuity equation (CE) using peak velocities (CEVpeak), mean velocities (CEVmean), velocity-time integrals (CEVTI) and the pressure half time method using 220 ms as constant first (PHT220) as well as optimized constants. In 267 consecutive patients with normally functioning MP, we investigated VA within the first postoperative month. With increasing prosthetic sizes, mean VA values also increase in all calculations. The statistical curves demonstrate no significant difference in graphical steepness but show different levels. Comparison of mean VA showed the known systematic higher values of PHT220 and significantly decreased results when using CEVTI. This systematic difference between mean VA applying PHT220 versus CEVTI is approximately 1.0 cm(2) for all prosthetic sizes. Calculations via CEVpeak were close to the results of CEVTI. CEVmean produced values, which graphically correspond to the PHT220 curve. Only PHT220 detected the constructional equal prosthetic inner ring width between 29 and 31 mm. To compensate the systematic difference between CEVTI and PHT220, an optimized constant of 140 ms was calculated to be applied in PHT (PHT140). VA is a robust and, therefore, preferable parameter for investigating MP. If needed, both CE and PHT are applicable with a systematical difference between CEVTI and PHT220. An optimized constant of 140 ms (PHT140) should be applied when calculating VA of mitral valve prostheses via PHT.