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Mechanical Restitution of Contractility in Stunned Myocardium of Open-Chest Dogs

  • Published:
Cardiovascular Engineering: An International Journal

Abstract

The aim of the present study was to determine the interval–contractility relationship in the same myocardial area before and after ischemia, thereby testing the hypothesis that calcium handling is impaired in stunned myocardium. Myocardial stunning was created by 15-min occlusion of the left anterior descending branch of coronary artery (LAD) followed by reperfusion in 10 open-chest dogs. Complete atrioventricular (A-V) block was achieved by injecting formaldehyde into the A-V node and the heart was paced by right ventricular electrodes. Extrasystoles at various intervals were then produced by electrical stimulation after cessation of regular pacing. Miniature force gauges were used to assess contractility. Mechanical restitution curves (MRCs) were constructed in the LAD area before and after stunning, by plotting normalized contractility against extrasystolic intervals (ESIs). The MRC was fitted to the monoexponential function FRn = FRmax {1 − Exp[(ESI-ESI0)/T c]}, where FRn is normalized contractile force, FRmax is the maximal value of a contractile response, T c is the time constant for restitution, and ESI0 is the smallest ESI that produced a mechanical response. After occlusion–reperfusion, FRmax decreased from (136.5 ± 8.2)% to (111.2 ± 5.4)%, whereas T c and ESI0 remained unchanged. These results suggested preserved sarcoplasmic reticulum function in stunned myocardium, but that the responsiveness of the contractile machinery is depressed.

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Authors and Affiliations

  1. Department of Physiology and Biophysics, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey

    Xu Wang, Guangping Li, Yi Ren & Joseph Kedem

  2. Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey

    Gary Drzewiecki & John K-J. Li

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  1. Xu Wang
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  2. Guangping Li
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  3. Yi Ren
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  4. Gary Drzewiecki
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  5. John K-J. Li
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  6. Joseph Kedem
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Wang, X., Li, G., Ren, Y. et al. Mechanical Restitution of Contractility in Stunned Myocardium of Open-Chest Dogs. Cardiovascular Engineering 2, 57–65 (2002). https://doi.org/10.1023/A:1020929319284

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