Paradoxic decrease in ischemic mitral regurgitation with papillary muscle dysfunction - Insights from three-dimensional and contrast echocardiographywith strain rate measurement

Background-Ischemic mitral regurgitation (MR) was first ascribed to papilla ry muscle (PM) contractile dysfunction. Current theories include apical lea flet tethering caused by left ventricular (LV) distortion, but PM dysfuncti on is still postulated and commonly diagnosed. PM contraction, however, par allels apical tethering, suggesting the hypothesis that PM contractile dysf unction can actually diminish MR due to ischemic distortion of the inferior base alone. Methods and Results-We therefore occluded the proximal circumflex circulati on in 7 sheep while maintaining PM perfusion, confirmed by contrast echocar diography. By 3D echocardiography, we measured the tethering distance betwe en the ischemic medial PM tip and anterior annulus and LV ejection volume t o give MR (by subtracting flowmeter LV outflow). In 6 sheep without initial MR, inferior ischemia alone produced PM tip retraction with restricted lea flet closure and mild-to-moderate MR (regurgitant fraction, 25.2 +/-2.8%). Adding PM ischemia consistently decreased MR and tethering distance (5.2 +/ -0.3 to 1.4 +/-0.3 mL; +3.8 +/-0.5 min to -2.2 +/-0.7 turn axially relative to baseline; P <0.001) as PM strain rate decreased from +0.78 +/-0.07 per second (contraction) to -0.42 +/-0.06 per second (elongation, P <0.001) and leaflet tenting decreased. In one sheep, prolapse and MR resolved with int erior ischemia and recurred with PM ischemia. Conclusions-PM contractile dysfunction can paradoxically decrease MR from i nferobasal ischemia by reducing leaflet tethering to improve coaptation. Th is emphasizes the role of geometric factors in ischemic MR mechanism and po tential therapy.