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Eur J Cardiothorac Surg 2007;32:96-101. doi:10.1016/j.ejcts.2007.03.043
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved

The papillary muscles as shock absorbers of the mitral valve complex. An experimental study

^a The International Heart Institute of Montana Foundation at Saint Patrick Hospital and Health Sciences Center and The University of Montana, Missoula, Montana, USA
^b Service de Chirurgie Cardiaque, Hôpital Bichat, Paris, France

Received 3 January 2007; accepted 30 March 2007.

^_* Corresponding author. The International Heart Institute of Montana Foundation, 554 West Broadway, Missoula, MT 59802, USA. Tel.: +1 406 329 5668; fax: +1 406 329 5880. (Email: duran{at}saintpatrick.org).

Objective: Although it is known that the papillary muscles ensure the continuity between the left ventricle (LV) and the mitral apparatus, their precise mechanism needs further study. We hypothesize that the papillary muscles function as shock absorbers to maintain a constant distance between their tips and the mitral annulus during the entire cardiac cycle. Materials and methods: Sonomicrometry crystals were implanted in five sheep in the mitral annulus at the trigones (T1 and T2), mid anterior annulus (AA) mid posterior annulus (PA), base of the posterior lateral scallops (P1 and P2), tips of papillary muscles (M1 and M2), and LV apex. LV and aortic pressures were simultaneously recorded and used to define the different phases of the cardiac cycle. Results: No significant distance changes were found during the cardiac cycle between each papillary muscle tip and their corresponding mitral hemi-annulus: M1–T1, (3.5 ± 2%); M1–P1 (5 ± 2%); M1–PA (5 ± 3%); M2–T2 (2.7 ± 2%); M2–P2 (6.1 ± 3%); and M2–AA (4.2 ± 3%); (p > 0.05, ANOVA). Significant changes were observed in distances between each papillary muscle tip and the contralateral hemi-mitral annulus: M1–T2 (1.7 ± 3%); M1–P2 (23 ± 6%); M1–AA (6 ± 3%); M2–T1 (8 ± 3%); M2–P1 (10.5 ± 6%); and M2–PA (12.6 ± 8%); (p < 0.05 ANOVA). The distance changes between LV apex and each papillary muscle tip were significantly different: apex–M1 (12.9 ± 1%) and apex–M2 (10.5 ± 1%) and different from the averaged distance change between the LV apex and each annulus crystal (8.3 ± 1%) with p < 0.05. Conclusion: The papillary muscles seem to be independent mechanisms designed to work as shock absorbers to maintain the basic mitral valve geometry constant during the cardiac cycle.

Key Words: Anatomy • Mitral valve • Regurgitation • Papillary muscles • Surgery