[Doppler estimation of the stenotic mitral valve area. Direct application of the continuity equation to the flow convergence region]

The continuity equation, applied to the flow convergence region (FCR), fournishes a simple alternative to calculate stenotic valve area. The flow rate in the FCR can be calculated by multiplying the hemispheric isovelocity surface area by the velocity of the isovelocity surface. Since according to the continuity principle the flow rate through any isovelocity surface equals the flow rate through the stenotic orifice, the stenotic orifice area can be calculated as: 2 pi r2Vr/Vm, where 2 pi r2 is the hemispheric isovelocity area, Vr is the velocity at the radial distance r from the orifice and Vm is the peak jet velocity. This study was designed to analyze the validity of application of the continuity equation to the FCR for estimating mitral orifice area by Dopler ultrasound. We studied 35 consecutive patients with rheumatic mitral stenosis. Three patients were excluded; the final study population consisted of 32 patients (8 men and 24 women; mean age 56 years). Nine patients were in normal sinus rhythm and 23 in atrial fibrillation. Doppler examination was performed from the apical approach within 24 hours of cardiac catheterization. On color Doppler image Vr was defined as the first aliasing limit (lowered to 38 cm/s to increase FCR r); r represented the maximal early diastolic distance between the first alias and the stenotic orifice in a direction parallel to that of the transducer; Vm was the early diastolic peak jet velocity by continuous wave Doppler.(ABSTRACT TRUNCATED AT 250 WORDS)