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The left circumflex coronary artery was li gated in anesthetized dogs, and the blood flow to the normal and ischemic regions was esti mated by means of the Rb86 clearance tech nique. Time occlusion of this coronary artery resulted in an appreciable reduction in the Rb86 clearance, principally in the posterior region of the left ventricle bounded by the circumflex artery, the posterior descending branch, the ramus marginis obtusi, and the apex. The diminution of clearance of this iso tope was most marked in the basal region, and imp roved progressively toward the apex. Clearances were also decreased in the basal regions just anterior and posterior to this zone. The weight of the ischemic zone, as defined by the Rb clearance technique, was approxi matelv half of that outlined in other studies by injection of dye into the distal end of the occl.uded circumflex artery. Th.is implies that the marginal zone of the territory supplied by the left circumflex coronary artery must receive a dual blood supply. Also, the Rb86 clearance in the ischemic zone exceeds the es timates of collateral flow l) rovided by simul taneously measured ietrogracle flows. This was true despite the facts that (a) actual blood flows must exceed the measured R clear ances, since extraction is never complete, and (b) retrograde flows overestimate the true value for interarterial collateral flow. When the interarterial collateral flow is drained away by leaving the low resistance cannula system uriclamped during the isotope inf u sion, the Rb86 clearance is not appreciably af fected in the marginal zone and is reduced by 50 to 60 per cent in the central and basal Portions of the ischemic region. rphese find ings signify that an appreciable circulation must be provided by vessels which communi cate with the capillary beds within the ische inic zone anc1, therefore, would contribute to the measured retrograde flow to only a neg ligible extent.

Collateral Blood Flow to the Myocardium as Determined by the Clearance of Rubidium 86 Chloride

Collateral Blood Flow to the Myocardium as Determined by the Clearance of Rubidium ⁸⁶ Chloride