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Mechanism of dynamic regurgitant orifice area variation in functional mitral regurgitation

Physiologic insights from the proximal flow convergence technique

Judy Hung, MD^*, Yutaka Otsuji, MD^*, Mark D. Handschumacher, BS^*, Ehud Schwammenthal, MD, PhD and Robert A. Levine, MD, FACC^*

^* Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Boston, Massachusetts, USA
Heart Institute, Chaim Sheba Medical Center, Tel Hashomer, Israel

View larger version (21K): [in a new window]   Figure 1 Schematic of PFC technique. As flow approaches a finite orifice, it forms isovelocity shells which by conservation of mass can be used to calculate the regurgitant flow rate. The regurgitant flow rate equals the surface area of the isovelocity shell times its velocity. Hence, flow rate equals (2r2)v where r is the radius of a hemispheric shell. An M-mode cursor is aligned along the maximal radius (r) of the PFC region to obtain a color Doppler M-mode of the PFC region (upper right); instantaneous ROA is then obtained as instantaneous flow rate/orifice velocity (obtained by continuous-wave Doppler).

View larger version (36K): [in a new window]   Figure 2 Color M-mode of PFC region. Figure 2A shows a digital image of a color M-mode of the PFC region with small arrows pointing to the mitral leaflet and large areas pointing to direction of regurgitant flow from LV to LA. Figure 2B shows the contour of the PFC region with the velocity set at times the Nyquist limit. This velocity contour and mitral leaflets were then traced to obtain instantaneous radii as shown in Figure 2C (see text for further details).

View larger version (23K): [in a new window]   Figure 3 The temporal pattern of the normalized values for MAA, TMP and ROA are shown for four representative patients. In all patients there is a biphasic pattern for ROA with a rapid decrease from its early systolic peak and a rapid increase toward its late systolic peak with a midsystolic decrease. Although MAA also peaked in early and late systole, its changes were more gradual and over a narrower range. In contrast, TMP showed wide and rapid changes in early and late systole mirroring the time course of ROA.

View larger version (20K): [in a new window]   Figure 4 Relationship of ROA vs TMP and MAA. The upper panels show an inverse relationship over a full range for ROA and TMP whereas the bottom panels show that the ROA varies over a much narrower range with MAA.

View larger version (13K): [in a new window]   Figure 5 The temporal pattern of a patient with a Carpentier-Edwards mitral ring and functional MR is displayed in Figure 5, left panel. With a fixed mitral annulus, there is the persistence of a similar biphasic temporal pattern of the ROA observed in patients with functional MR without rings in place. Figure 5, right panel, shows a similar reciprocal relationship of ROA and TMP in this patient that is also observed in patients with functional MR without mitral rings.

View larger version (27K): [in a new window]   Figure 6 Schematic of the force balance on the mitral leaflets. Increased tethering forces from a dilated LV oppose the force of TMP which acts to close the leaflets.