Quantitative relationships between thallium-201 estimated myocardial infarct size and left ventricular function in the acute or convalescent phase of the first attack of myocardial infarction

Correlations between left ventricular (LV) function and infarct size estimated by computer-assisted thallium (Tl)-201 scintigraphy were studied in 16 patients in the acute or convalescent phase of the first attack of transmural myocardial infarction (MI). Tl-201 estimation of the infarct size was done using a "corrected" circumferential profile method, by which the total defect score could be obtained. The LV function was evaluated by radionuclide angiography, echocardiography and cardiac catheterization study. The following results were obtained : 1) A close inverse relationship was found between the defect score and the ejection fraction (r=-0.649, r<0.01). 2) The linear correlation diastolic pressure and -0.616 (p < 0.02) between the defect score and the cardiac index. 3) There was a linear correlation between the defect score and the LV end-diastolic dimension (r= -0.852, p < 0.001). However, there was no relation between the defect score and the left atrial dimension. When the LV indices were compared between the small (S) and the large (L) defect score group, the L defect group had faster heart rate, larger LV chamber size and the smaller stroke volume index than the S defect group. However, there was no significant difference in the cardiac index between these 2 groups. These results suggest that the LV dilatation in acute or convalescent phase of the first attack of transmural MI is an ominous sign because it was usually accompanied by large infarct size. The present study also indicates that LV dilatation accompanying a large infarct does not satisfactorily compensate for LV dysfunction by Frank-Starling mechanism, because the stroke volume index decreased in proportion to the infarct size and the cardiac index was maintained by an increase in heart rate in cases with LV dilatation.