Key result
Papillary muscle tip to mitral annulus distance remains unchanged during the cardiac cycle in sheep.
Why the study?
The precise mechanism by which papillary muscles maintain continuity between the left ventricle and the mitral apparatus requires further study.
Answers are grounded in this paper and cite their sources.
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.
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Joudinaud et al. (2007) studied this question. Sonomicrometry crystal implantation and distance measurement was evaluated on Distance changes between papillary muscle tips and mitral annulus during the cardiac cycle (p=>0.05). In an experimental sheep model, no significant distance changes occurred between each papillary muscle tip and their corresponding mitral hemi-annulus during the cardiac cycle (p>0.05).
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