Summary:A new technique of data processing, the unfolded map methcd, was used with thallium-20 I single-photon emission computed tomography to quantify infarct size in 35 patients wilh single-vessel disease at 4 weeks after their first myocardial infarction (24 anterior and 11 inferior infarcts), and the results were cornpared with those obtained by electrocardiography and contrast left ventriculography. The myocardial borders and the infkcted region were defined using the threshold technique and a cutoff value of 55%. Count profile data for each short-axis slice were unfolded zonally into single planes with the same riltio, and their areas were calculated from the slice thickness and radius. Thus, the size ol'the unfolded map represented the actual left ventricular myocardial area Infarct size was quantitated from the ratio of pixels in the infarcted region to those in the whole map, and the ratio itself was used as the percent infarct six. Although a defect I cni in diameter (0.8 cm?) could not be detected in a phantom study, defects 2 2 cm in diameter (2 3. I cm?) could be measured satisfactorily. The infarct size and percent infarct size determined by the unfolded map method correlated well with the QRS score (r = 0.841 and r = 0.838), the percentage of abnormally contracting segments on left ventriculography (r = 0.835 and r = 0.87 7). and the ejection frnction (r = -0.835 and r = -0.856). These data indicate that the unfolded map method provides adequate quantification of infarct siLe, even in the chronic phase, without complicated data processing.

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The significance of exercise-induced S-T elevation in aVR was studied in 57 patients with recent anterior infarction and single-vessel disease. S-T elevation in aVR was found at peak exercise in 24 patients. Although the initial defect area was similar in the groups with and without S-T elevation in aVR, the redistribution area was larger in the former group (p < 0.01). When three electrocardiographic criteria were used in the multivariate analysis, S-T elevation in aVR was the significant variable related to redistribution in the anterior wall. Thus, S-T elevation in aVR may indicate ischemia of the anterior wall.

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