The Effect of Regional Myocardial Heterogeneity on the Economy of Isometric Relaxation

  • Norman R. Alpert
  • Louis A. Mulieri


This chapter is directed at clarifying the relationship between regional myocardial heterogeneity and the economy of contraction and relaxation [1]. When heart muscle contracts and relaxes isometrically, there is considerable internal shortening and lengthening during the rise and fall of tension development [2]. In-skeletal muscle, under those conditions where active muscle shortens and lengthens, the energetic cost of shortening is greater than that of lengthening [3–6]. Thus the economy of contraction is less than that of relaxation. If heart muscle is like skeletal muscle, one would expect the economy of relaxation to be greater than that of contraction. Inhomogeneity adds another dimension to this problem. Inhomogeneity is present in normal hearts and abounds under pathological conditions. In normal hearts there are geometric (apex to base) [7–10] and isoenzymic [11–16] differences. In the presence of regional ischemia, the stunned portion of the heart is much weaker than the nonstunned portion [17, 18]. When an infarct occurs, the noninfarcted remainder of heart may hypertrophy with the extent of the hypertrophic response being different in the various areas [19–22]. This heterogeneity results in a functional difference in myocytes or sarcomeres, which are in series with each other. How these differences affect the predicted increase in economy of isometric relaxation in contrast to contraction is the focus of this chapter.


Papillary Muscle Rabbit Heart Relaxation Phase Initial Heat Ventricular Papillary Muscle 
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© Martinus Nijhoff Publishing 1987

Authors and Affiliations

  • Norman R. Alpert
  • Louis A. Mulieri

There are no affiliations available

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