Nature of the border zone of myocardial ischemia after coronary artery occlusion in the dog

After coronary occlusion a zone of intermediate flow is found between ischemic and normal myocardium. To determine to what extent this border zone represents a true gradient of collateral flow from center to edge, selective intracoronary (IC) 7-10 μ radioactive micropheres (M) were used to mark the myocardium fed at rest by the anterior descending (LAD) and circumflex arteries (LC). The LAD and LC were separately perfused from the femoral arteries. Peripheral coronary pressure, peak reactive hyperemia, resting flow, and inner/outer wall flow were similar in LAD and LC regions. Passage of ICM to the opposite region was <0.5%, M were then injected into the left atrium 30 sec after LAD ligation and flow determined in 5 mm tissue samples through the border zone. In the center of the ischemic LAD region, mean flow was 0.08±0.3 ml/min/g (SEM, 8 dogs). Flow was higher at the edge even when samples with any LCM were excluded. Mean flow was 0.12 ml/min/g in the outermost 5 mm of samples without LCM (p<.02 vs center). In samples containing both LAD and LCM, most of the total flow was accounted for by flow to non-ischemic LC tissue, as calculated from the LCM content. However, corrected collateral flow was 0.18±0.3 ml/min/g, more than twice the central ischemic value (p<.02). The extent of this LC-LAD overlap zone varied from 7-14 mm (mean 9.5). Thus, immediately after coronary occlusion the border zone was related not only to mixture of ischemic and non-ischemic tissue, but also to a true gradient of collateral flow. The spatial extent of this increased collateral flow was substantial, averaging 18.3 mm.