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Abstract
Imaging of the flow convergence region (FCR) proximal to a regurgitant orifice has
been shown to provide a method for quantifying the regurgitant flow rate. According
to the continuity principle, the FCR is constituted by concentric hemispheric isovelocity
surfaces centered at the orifice. The flow rate is constant across all isovelocity
surfaces and equals the flow rate through the orifice. For any isovelocity surface
the flow rate (Q) is given by: Q = 2 pi r2 Vr, where 2 pi r2 is the area of the hemisphere
and Vr is the velocity at the radial distance (r) from the orifice.
We studied 52 consecutive patients with mitral regurgitation (mean age, 49 years;
age range, 21-66 years) verified by left ventricular angiography using color flow
mapping. The FCR r was measured as the distance between the first aliasing limit--at
a Nyquist limit obtained by zero-shifting the velocity cutoff to 38 cm/sec--and the
regurgitant orifice. Seven patients without evidence of an FCR had only grade 1+ mitral
regurgitation angiographically. There was a significant relation between the Doppler-derived
maximal instantaneous regurgitant flow rate and the angiographic degree of mitral
regurgitation in the other patients (rs = 0.91, p less than 0.001). The regurgitant
flow rate by Doppler also correlated with the angiographic regurgitant volume (r =
0.93, SEE = 123 ml/sec) in the 15 patients in normal sinus rhythm and without other
regurgitant lesions in whom it could be measured. The correlation between regurgitant
jet area within the left atrium and the angiographic grade was only fair (rs = 0.75,
p less than 0.001).
Color flow Doppler provides new velocity information about the proximal FCR in patients
with mitral regurgitation. According to the continuity principle, the maximal instantaneous
regurgitant flow rate, obtained with the FCR method, may provide a quantitative estimate
of the severity of mitral regurgitation, which is relatively independent of technical
factors.