An analysis of myocardial infarction. The effect of regional changes in contractility.

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Abstract
In a preceding paper, we employed an initially spherical, modified membrane model of the infarcted ventricle to investigate the relation between ventricular function and both infarct size and infarct stiffness. In the present paper, we have applied the same model to a set of different questions, namely, the consequences of enhanced or depressed inotropic state within the noninfarcted myocardium. When infarcted ventricles containing up to 41% infarction are examined, stroke volume appears to be relatively insensitive to increases in inotropic state. However, stroke volume falls rapidly when inotropic state is depressed below 80% of normal. For the case of a ventricle with a large, weakly contracting segment which is not totally infarcted, stroke volume is impaired only when the contractility of the weak region is diminished below 50% of normal. Finally, the stress concentration around a region of infarction appears to be dependent more strongly on the inotropic state of the noninfarcted tissue than on the infarct size.