Papillary muscle misalignment causes multiple mitral regurgitant jets: An ambiguous mechanism for functional mitral regurgitation

Background and aims of the study: The study aim was to test the hypothesis that asymmetric alignment (misalignment) of the papillary muscles is sufficient to cause incomplete mitral leaflet coaptation and functional mitral regurgitation (MR). Methods: Different spatial relationships between the papillary muscles and the mitral annulus were investigated in isolated porcine mitral valves in vitro to assess the impact on mitral valve competence. The systolic occlusional leaflet area (OLA) needed to cover the mitral orifice and the anterolateral (ACOM) and posteromedial (PCOM) commissural portion (OLA(ACOM), OLA(PCOM)) were assessed by 2D echocardiography to quantitate incomplete mitral leaflet coaptation. The regurgitant fraction (RF) and MR jet location were assessed by a flow meter and color Doppler ultrasound. Results: Posterolateral dislocation of the posteromedial papillary muscle impaired mitral leaflet coaptation at the corresponding half-portion of the mitral orifice (OLA(PCOM): 351-397 mm² versus 296 mm² (normal); p < 0.001) and modified the contralateral part (OLA(ACOM): 354-387 mm² versus 304 mm² (normal); p <0.001). The mitral leaflet coaptation line moved in apical and posterior directions, creating a commissural MR orifice at the PCOM side. At the ACOM side, anterior leaflet prolapse and restricted posterior leaflet mobility created an additional commissural regurgitant jet (RF = 0.11-0.13). Symmetrical papillary muscle misalignment restricted mitral leaflet mobility on both sides of the orifice in a synergistic manner (OLA(PCOM): 416-459 mm² and OLA(ACOM): 427-489 mm²; both p <0.001 versus normal). The central MR jet orifice, which extended towards both commissures, caused more significant MR (RF = 0.15-0.26). Conclusions: Papillary muscle misalignment caused mitral regurgitant jet ambiguity with an anterior MR jet location following posteromedial papillary muscle displacement. These findings may improve understanding of the relation between myocardial lesion and mitral regurgitant jet location and thereby facilitate rational strategies for valvular interventions.