PHYSICAL BASIS FOR THE MITRAL VELOCITY CURVE IN ASSESSING MITRAL-VALVE AREA AND LEFT-VENTRICULAR DIASTOLIC FUNCTION

The temporal pattern of blood velocity through the mitral valve is used to assess mitral valve area and ventricular diastolic function. In routine empirical implementation, it is often assumed in mitral stenosis that mitral valve area alone determines the pressure half-time, while in assessing diastolic function, the effects of the mitral value are often ignored. Clearly these situations cannot be completely separated: chamber properties and mitral valve impedance affect ventricular filling in both cases. In this review, a unified approach to the analysis of mitral in flow patterns is presented. Through theoretical analysis, computer simulation, in vitro modeling, and clinical data, it is shown that mitral acceleration varies directly with the atrioventricular pressure difference early in diastole and inversely with the inertance of blood within the mitral apparatus. Similarly, mitral deceleration rate is directly proportional to the effective area of the mitral valve and inversely related to the net compliance of the atrium and ventricle. In the setting of mitral stenosis, this means that the mitral pressure half-time is inversely proportional to mitral valve area (as commonly implemented clinically), but also directly related to net chamber compliance and the square root of the initial transmitral pressure difference. In evaluation of diastolic function, this explains the steep mitral deceleration observed in restrictive cardiomyopathies. An appreciation of the physical issues governing ventricular filling should warn of potential pitfalls in the Doppler evaluation of mitral valve area and ventricular function, as well as suggest more quantitative approaches based on these principles.