Left Ventricular Size and Function and Heart Size in the Year Following Myocardial Infarction

Interrelationships among left ventricular (LV) size, LV function, and heart size were investigated in 49 patients studied 2-12 months after myocardial infarction. LV end-diastolic volume (EDV) and ejection fraction (EF) were determined by biplane ventriculography. Heart size was estimated from chest films by the cardiothoracic ratio (CTR) and cardiac volume (CV) methods. Ventricular function (i.e., EF) was related to chamber size (i.e., EDV), but the correlation coefficient was not high (r = 0.74); thus, chamber size was not an accurate predictor of EF. Because of the close linear relation that exists between LV end-systolic volume and EDV (r = 0.98), a hyperbola describes the relation between EF and EDV. In general, EF was depressed (<0.50) when EDV exceeded 70 ml/m2, was <0.35 when EDV exceeded upper normal limits (110 ml/m2), and was <0.25 with chamber size >150 ml/m2. Thus relatively small chamber size (<150 ml/m2) was associated with a wide range in ventricular function, while large chamber size was associated with severe dysfunction (EF < 0.30). By either heart size method, cardiomegaly (CTR > 0.50 or CV > 540 ml/m2) was not found consistently until EDV exceeded 150 ml/m2. Hence normal heart size was often associated with moderate EF depression (0.49-0.30), while cardiomegaly was often associated with severe dysfunction. Clinical heart failure (CHF) was usually accompanied by EF < 0.30, but chamber size ranged from 101 to 331 ml/m2. Primarily because of this variation in chamber size, both normal heart size and cardiomegaly were at times associated with CHF.The poor correlations of EF with CTR (r = −0.43) and CV (r = −0.52) preclude use of the heart size indices as accurate predictors of LV function. When the data were analyzed according to the presence or absence of cardiomegaly, the following generalizations could be made regardless of the heart size method used. Cardiomegaly was a reasonable indicator of postinfarction LV function, being associated with depressed function and often with CHF. However normal heart size was associated with either normal LV function, or commonly, with depressed function, often not clinically apparent.