Pathogenesis of mitral regurgitation in tachycardia-induced cardiomyopathy

Background-Dilated cardiomyopathy is often associated with mitral regurgita tion (MR), or so-called functional MR, the mechanism of which continues to be debated. We studied the valvular and ventricular 3D geometric perturbati ons associated with MR in an ovine model of tachycardia-induced cardiomyopa thy (TIC). Methods and Results-Nine sheep underwent myocardial marker implantation in the left ventricle (LV), mitral annulus. and mitral leaflets. After 5 to 8 days, the animals were studied with biplane videofluoroscopy (baseline), an d mitral competence was assessed by transesophageal echocardiography. Rapid ventricular pacing (180 to 230 bpm) was subsequently initiated for 15 +/-6 days until the development of TIC and MR, whereupon biplane videofluorosco py and transesophageal echocardiography studies were repeated. LV volume wa s calculated from the epicardial marker array. Valve closure time was defin ed as the time after end diastole when the distance between leaflet edge ma rkers reached its minimal plateau. TIC resulted in increased LV end-diastol ic volume (P=0.001) and LV end-systolic volume (P=0.0001) and greater LV sp hericity (P=0.02). MR increased significantly (grade 0.2 +/-0.3 versus 2.2 +/-0.9, P=0.0001), as did mitral annulus area (817 +/- 146 versus 1100 +/- 161 mm(2), P=0.0001) and mitral annulus septal-lateral diameter (28.2 +/-3. 5 versus 35.1 +/-2.6 nim, P=0.0001). Time of valve closure (70 +/- 18 versu s 87 +/- 14 ms, P=0.23) and angular displacement of both the anterior (29 /-5 degrees versus 27 +/-3 degrees, P=0.3) and posterior (55 +/-5 degrees v ersus 44 +/- 11 degrees, P=0.13) leaflet edges relative to the mitral annul us after valve closure did not change, but leaflet edge separation after cl osure increased (5.2 +/-0.9 versus 6.8 +/-1.2 mm, P=0.019). Conclusions-MR in TIC resulted from decreased leaflet coaptation secondary to annular dilatation in the septal-lateral direction. These data support t he use of annular reduction procedures, such as rigid, complete ring annulo plasty, to address functional MR in patients with dilated cardiomyopathy.