Papillary muscle approximation reduces systolic tethering forces and improves mitral valve closure in the repair of functional mitral regurgitation

Papillary muscle approximation relieves tethering forces on the mitral valve and enables good correction of functional mitral regurgitation.

Figure 1. Papillary muscle approximation reduces the ventricular tethering forces and restores physiological leaflet mobility and systolic coaptation when used concomitantly with undersizing mitral annuloplasty in the repair of functional mitral regurgitation. FMR, Functional mitral regurgitation; UMA, undersizing mitral annuloplasty; PMA, papillary muscle approximation.

Figure 2. A, Photograph of the pulsatile left heart simulator used in this study, consisting of an acrylic left heart model with a native pig mitral valve, with the model placed in a closed flow loop. This setup is connected to a programmable pump to generate physiological pressures and flows through the circuit. B, Ventricular view of the pig mitral valve mounted into this acrylic model. The annulus is sutured onto the D-shaped ring, and the papillary muscles are mounted onto rods whose spatial position can be altered. C, Different configurations of the mitral valve, with apical, lateral, and posterior displacement of the papillary muscles. LV, Left ventricle; MV, mitral valve; LA, left atrium.

Figure 3. A, Deconstructed components of the adjustable annuloplasty ring. B, The adjustable annuloplasty ring mounted onto a 3-dimensional printed catheter to enable its size adjustment outside the pulsatile flow loop. C, Surgeon's view of the mitral valve in the flow loop, with and without the annuloplasty ring. D, Miniature force transducers developed to measure chordal forces. A transducer is shown to depict its size, and a photograph with transducers mounted onto the marginal and strut chordae is shown. 3D, 3-dimensional.

Video 1. Oral narrative of the biomechanical effects of papillary muscle approximation on the mitral valve in functional mitral regurgitation. Video available at: https://www.jtcvs.org/article/S2666-2736(21)00089-9/fulltext.

Figure 4. A, Changes in regurgitant fraction before and after different repairs. Undersizing mitral annuloplasty (UMA) with a 30-mm or 26-mm ring reduced the mitral regurgitation, but were not significantly different than the pre-repair condition. The addition of papillary muscle approximation (PMA) after both sizes of annuloplasty reduced the regurgitant fraction significantly compared with the disease state. The regurgitation fractions after PMA were not different from the baseline/predisease state. B, The tenting area was higher in the diseased group compared with baseline, as a result of the geometric distortions imposed on the valve. After UMA, the tenting area was reduced, but was not statistically significant. With PMA, the tenting area was significantly lower than that with the corresponding annuloplasty alone and compared with the diseased state. C, Tenting height was measured at the central A2-P2 cusps; its changes under different experimental conditions are shown. Identical trends as for tenting area were observed. D, Systolic leaflet coaptation length was significantly reduced in the disease state compared with baseline. Annuloplasty did not significantly alter the leaflet…

Figure 5. Leaflet mobility was quantified in diastole (diastolic angle) and systole (systolic angle), and the excursion angle was defined as the difference between the two. A, The anterior diastolic angle was significantly altered from baseline when functional mitral regurgitation was induced by tethering the valve. Neither true-sized nor downsized annuloplasty improved this angle. The addition of papillary muscle approximation (PMA) to annuloplasty significantly increased the diastolic angle, indicating that better valve opening was possible. The anterior systolic angle was not significantly altered in any of the groups. The anterior excursion angle was decreased in the diseased state and was not improved after annuloplasty of either size. The addition of PMA significantly improved the excursion angle. B, The posterior diastolic and systolic angles and the excursion angles were not significantly altered under the different conditions. Data are depicted in a box-and-whiskers plot. The horizontal line in each box is the median, and the 2 whiskers indicate the minimum and maximum of the distribution. FMR, Functional mitral regurgitation; TSR, true-sized ring; DSR, down-sized ring.

Figure 6. Temporal changes in chordal forces under different experimental conditions. Each trace is an average of data from 10 valves, and each valve's data is an average of 15 consecutive cardiac cycles. (Top row) Differences in the chordal forces between baseline/healthy valve configuration and the functional mitral regurgitation condition in which the mitral annulus is dilated and the papillary muscles are displaced outwardly. A significant rise in the peak force was seen in both the anterior strut and marginal chordae, but such a rise was not observed in the posterior mitral leaflet. (Middle row) The impact of mitral annuloplasty, both true-sized ring (TSR) and down-sized ring (DSR). Both TSR and DSR minimally reduced the peak forces in the chordae tendineae. (Bottom row) The impact of concomitant papillary muscle approximation (PMA) on the force distribution. Adding PMA significantly reduced the peak chordal forces in all the chordae with both TSR and DSR; FMR, Functional mitral regurgitation.

Figure 7. Peak systolic chordal forces under each experimental condition. A, Peak anterior strut chordal forces under different experimental conditions. The greatest reduction in the chordal forces compared with the disease state was achieved with papillary muscle approximation (PMA). B, Peak posterior strut chordal forces demonstrated a significant reduction with PMA compared to the disease state and also compared to the corresponding level of annuloplasty. C, PMA reduced the anterior marginal chordal forces in some conditions but not in others. D, Peak posterior marginal chordal forces were significantly lower with PMA. FMR, Functional mitral regurgitation; TSR, true-sized ring; DSR, down-sized ring.

Figure 8. Schematic of the mechanistic basis for improved mitral valve hemodynamics and mechanics with papillary muscle approximation (PMA). A1, A healthy heart with a competent mitral valve, in which the shortening of the interpapillary muscle distance from diastole to systole enables slackness in the chordae tendineae of the mitral valve, enabling better leaflet mobility and systolic coaptation. A2, A failing and dilated heart in which poor ventricular contractility causes loss of interpapillary muscle shortening from diastole to systole. The separated papillary muscles impose a constant tethering force on the mitral valve leaflet edges in both diastole and systole. In systole, such tethering leads to loss of coaptation and mitral regurgitation. A3, On implantation of a downsizing annuloplasty ring in this heart with poor interpapillary muscle shortening, the tethering effect on the leaflets was worsened, although the smaller mitral area forced systolic leaflet coaptation. Such coaptation is not durable and leads to recurrent functional mitral regurgitation. A4, PMA relieves the tethering forces on the valve leaflets by eliminating the interpapillary muscle separation, resulting in a…

Figure E1. A, Equivalence between the custom-made adjustable undersizing mitral annuloplasty and different sizes of the commercial Physio annuloplasty ring (Edwards Lifesciences). B, En face view of the mitral valve at baseline after inducing functional mitral regurgitation with the 30-mm and 26-mm annuloplasty rings and after concomitant papillary muscle approximation. UMA, Undersizing mitral annuloplasty; FMR, functional mitral regurgitation; PMA, papillary muscle approximation.

Figure E2. A human cadaver heart in which papillary muscle approximation (PMA) was performed at the base of the muscles and at the tip. When PMA was done at the base, the muscle tips remained flayed apart and thus did not seem to have a beneficial effect on the valve. ALPM, Antero lateral papillary muscle; PMPM, postero medial papillary muscle.