Functional significance of hypertrophy of the noninfarcted myocardium after myocardial infarction in humans

Hypertrophy of the noninfarcted left ventricle as a chronic response to myocardial infarction has been demonstrated in animals and at autopsy in humans. However, the functional significance of postmyocardial infarction hypertrophy is a subject of dispute. The purpose of this study was to determine the time course of development of postmyocardial infarction hypertrophy of the noninfarcted myocardium in humans and to assess its functional significance. Subcostal view, two-dimensional echocardiograms were recorded at rest and during peak exercise, 6 and 40 weeks postmyocardial infarction in 45 patients (16 anterior, 20 inferior, nine non-Q wave infarcts), for measurement of left ventricular mass and ejection fraction. The left ventricular mass index increased from 94 +/- 30 to 118 +/- 27 g/m2 (p less than 0.01) during the time of the two studies. There was a significant correlation between the change in left ventricular mass index and improved resting ejection fraction (r = 0.48, p less than 0.001) and exercise ejection fraction (r = 0.48, p less than 0.001) at the follow-up study. Of the 32 patients who increased their left ventricular mass index greater than 7%, 18 improved their rest ejection fraction greater than 0.05 units and 17 improved their exercise ejection fraction greater than 0.05 units. Conversely, of the 13 patients who failed to increase their left ventricular mass index, only three improved their rest ejection fraction and one improved the exercise ejection fraction (Fisher's exact test, p less than 0.05). We reached three conclusions. First, in humans, significant hypertrophy of the noninfarcted myocardium can be detected by two-dimensional echocardiography, 9 months postmyocardial infarction.