Transmural variation in the relationship between myocardial infarct size and risk area

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Abstract
To determine if the relationship between Infarct area (IA) and area at risk (AR) varies in different layers of the left ventricle (LV), the circumflex coronary artery was occluded for 48 h in 20 conscious dogs. AR was determined by postmortem coronary stereoarteriography, and IA by pathological examination. Both AR and IA were divided into 4 layers, posterior papillary muscle (PPM), subendocardium (Endo), midwall and subepicardium (Epi), and quantified with planimetry. Hemodynamics and regional myocardial flow with tracer microspheres (7-10 .mu.m diameter) were measured before and after coronary occlusion. IA was closely correlated with AR for PPM (r = 0.96), Endo (r = 0.97) and Epi (r = 0.92). The slope of IA/AR for Endo (1.30 .+-. 0.08) was significantly steeper (P < 0.05) than that for Epi (0.89 .+-. 0.11). The intercepts at zero infarction of PPM (0.5 .+-. 0.1% of LV), Endo (4.2 .+-. 0.4%) and Epi (9.1 .+-. 0.7%) were significantly different from each other. Regional blood flow measurements indicate that the differences in IA/AR in various layers reflected earlier and greater total collateral flow to the noninfarcted AR in the epicardium. IA/AR for the entire LV is a composite representing separate IA/AR specific to various transmural layers of the LV. Apparently, the lateral border zone between the IA and the AR is minimal (< 3-5 mm) in the endo and midwall layers of the left ventricle.