Predictive Value of Anatomic Papillary Muscle Positioning for the Development of Mitral Valve Insufficiency

Objective: Papillary muscles (Pms) of the left ventricle actively participate in the coordinated opening of the mitral valve leaflets. They are an essential part of the mitral valve apparatus among the other elements (chordae, leaflets, and trabecula). Optimal opening requires right angular positioning of the Pms. This study addresses the question whether positions of Pms under physiological conditions vary and if its variation predispose for mitral valve insufficiency (MI).

Methods: For this study, cardiac CT scans from 272 patients were evaluated according to the left ventricular segmentation scheme (LVSS) conforming to the American Heart Association “scientific statements.” The positions of anterior papillary muscle (Pms_A) and posterior papillary muscle (Pms_B) were identified in each scan. Specific combinations were probed for being indicators of suspected mitral valve insufficiency in cases where echocardiography (echo) were additionally performed. Inside the left ventricle, angle between the Pms and the ventricular wall was measured with the special focus on patients with MI.

Results: Most frequent positions of Pms_A and Pms_B were found at the 10a and 10b areas or 12a and 12b areas according to the LVSS field, respectively. Most of the combinations were PmsA/B - 10b/12a< 10a12a< 10a/12b< and 10b/12b. Little difference was found in this order between men and women (PmsA/B - 10b/12a< 10a12a< 10b/12b< 10a/12b). When MI was confirmed by echo (regurgitation, MI I degree, MI II degree, Prolaps, and MI III degree) although the ventricle size remained normal, we found a 10a/12b combination in 50% and a 10b/12b combination in 60% cases. While in 59% of the MI investigated cases, the Pms_B was involved. On the contrary, an increased angle between Pms_B and ventricular wall (34.2 degrees) was found in the 12a position when MI appeared. At the 7a or 12b position, this angle was found to be smaller (32.6 and 32.8 degrees, respectively).

Conclusion: There are differences in the physiological positioning of Pms even at normal left ventricle geometry. In case studies of MI diagnosed by echo, the 10b/12b combination was most frequently found among all scans. Furthermore, measurements of the Pms angles indicating MI appear to be more intriguing. However, the question for insertion of Pms as origin for angular changes remains to be clarified.