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Impaired contractile reserve in severe mitral valve regurgitation with a preserved ejection fraction. | LitMetric

AI Article Synopsis

  • Chronic mitral valve regurgitation (MR) leads to contractile dysfunction in the heart, primarily due to issues with heart muscle cells rather than just increased load.
  • Researchers conducted experiments on dogs to analyze how MR affects heart function and calcium handling, comparing results between MR-affected dogs and control dogs.
  • The study found that despite maintaining normal ejection fraction, chronic MR was linked to reduced heart muscle performance and calcium cycling, indicating that the functional issues weren't simply due to the heart being overworked.

Article Abstract

Background: Impaired contractile reserve in chronic MR results from load-independent, myocyte contractile abnormalities.

Aims: Investigate the mechanisms of contractile dysfunction in chronic mitral valve regurgitation (MR).

Methods: Mild MR was produced in eight dogs followed by pacing induced left ventricular (LV) dilatation over eight months. In-vivo LV dP/dt was measured at several pacing rates. Contractile function was measured in isolated LV trabeculae and myocytes at several stimulation rates and during changes in extracellular [Ca2+]. Identical studies were performed with six control dogs.

Results: Chronic MR resulted in a preserved ejection fraction with decreased dP/dt (p<0.01). LV trabeculae demonstrated significantly lower developed force and a negative force-frequency relation with chronic MR (p<0.05). Myocytes exhibited a negative shortening-frequency relationship in both groups with a greater decline with chronic MR (p<0.001) paralleled by decreases in peak [Ca2+](i) transients. Increases in extracellular [Ca2+] abrogated the defects in force generation in trabeculae from animals with chronic MR.

Conclusion: Even with a preserved EF, chronic severe MR results in a significant reduction in intrinsic contractile function and reserve. Functional impairment was load-independent reflecting a predominant defect in calcium cycling rather than impaired peak force generating capacity due to myofibrillar attenuation.

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Source
http://dx.doi.org/10.1016/j.ejheart.2007.05.013DOI Listing

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