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Regurgitant flow in ischemic and dilative mitral regurgitation.

BACKGROUND AND AIM OF THE STUDY
It is well established that there are geometric differences between ischemic and dilative mitral regurgitation (MR), yet data on the hemodynamic consequences of these differences are scarce. The study aim was to determine whether mitral regurgitant flows in ischemic MR differ from those in dilative MR.


METHODS
A left heart simulator was developed to evaluate possible differences in regurgitant flows between two pathological mitral valve configurations, ischemic and dilative. Ischemic MR was simulated by increasing the baseline intercommissural diameter (CC) by 10%, the baseline septolateral (SL) diameter by 30%, and by displacing the posteromedial papillary muscle (PM) to the apical posterolateral position. Dilative MR was simulated by increasing the baseline SL and CC diameters by 30%, and by a symmetrical displacement of both PMs. Mitral regurgitant flow measurements were carried out under transmitral pressures ranging from 40 to 140 mmHg (increments of 15 mmHg). Camera snapshots of the mitral annulus were used to accurately determine mitral annular geometry by measuring the SL and CC diameters.


RESULTS
A total of 24 measurements was made on four porcine mitral valves; 14 to evaluate ischemic MR, and 10 to evaluate dilative MR. In ischemic MR, a constant regurgitant flow was observed throughout the pressure range tested. In dilative MR, increasing the transmitral pressure caused the regurgitant flows to decrease exponentially. The mitral annulus snapshot analysis showed that displacement of the posteromedial PM in ischemic MR caused the regurgitation orifice to appear at the tented side of the valve. An additional regurgitation orifice was formed through bulging (prolapse) of the leaflets at the contralateral commissure. The phenomenon was not observed in the dilative mitral valve configuration, where a central regurgitation orifice appeared with symmetrical PM displacement.


CONCLUSION
These data suggest that geometric differences between ischemic and dilative MR translate into significantly different hemodynamic properties of insufficient mitral valves.