Hemodynamic changes following experimental production and correction of acute mitral regurgitation with an adjustable...

The hemodynamic effects of acute mitral regurgitation (MR) were investigated using a newly designed adjustable mitral ring prosthesis with remote control mechanism, implanted in mongrel dogs. The prosthesis allows to dilate the mitral annulus from outside the beating heart, and to create reversible MR of any desired degree without injuring the mitral valve apparatus. Dilatation of the mitral annulus by 25% of its circumference led to MR of angiographic grade 3+. Left ventricular systolic pressure (LVSP) dropped by 20%; dp/dtmax of the left ventricle by 16% and forward cardiac output (CO) by 31%. Left ventricular enddiastolic pressure (LVEDP) rose by 41%. The amplitude of the v-wave of the left atrium (LA) doubled, and mean LA pressure rose by 33%. If correction was carried out within one hour, then all parameters returned to normal. Maintaining the same degree of annular dilatation for two hours led to a further marked deterioration of the hemodynamics. LVSP dropped by 40%, dp/dtmax by 32% and CO by 58%. LVEDP rose by 160%. The amplitude of the v-wave of the LA increased by 300% and mean LA pressure doubled. MR, as determined by contrast 2-dimensional echocardiography (2DCE) intraoperatively, further increased in severity during the second hour, though annular size remained unchanged. In contrast to correction after one hour, correction carried out after two hours led to a slow, and, even after 12 hours, incomplete recovery. Electron microscope studies suggest papillary muscle dysfunction as a major cause of these late and partially irreversible changes.