LABORATORY INVESTIGATION CORONARY BLOOD FLOW Collateral conductance changes during a brief coronary occlusion in awake dogs

Function of the coronary collateral circulation during the course of a single abrupt coronary occlusion was evaluated in awake dogs instrumented over the long term. Studies were performed approximately 2 weeks after collateral development had been stimulated in the dogs by partial stenosis of the proximal left circumflex coronary artery. The pressure drop from the central aorta to the distal circumflex coronary artery was measured continuously. Under control conditions and at 30 sec and 4 min of a single abrupt complete circumflex occlusion, myocardial blood flow was determined by a radioactive microsphere technique. Coronary collateral conductance was calculated as mean collateral blood flow divided by the mean drop in pressure. The following was noted in dogs that developed collateral vessels: during the coronary occlusion, mean distal circumflex coronary pressure increased from 42 + 9 to 49 10 mm Hg (p .01); mean collateral flow increased from 0.78 0.30 to 0.84 + 0.33 ml/min/g (p .05); the endocardial/epicardial flow ratio increased from 0.77 0.36 to 1.04 0.25 (p .01); and the coronary collateral conductance increased significantly from 0.017 + 0.017 to 0.021 0.021 (ml/min/g)/mm Hg (p .005). These data suggest that during a brief occlusion of a major coronary artery, immature coronary collateral channels do not reach maximal function immediately after the occlusion. Rather, coronary collateral conductance increases with time and may be associated with improved transmural perfusion of the myocardium. Circulation 72, No. 1, 225-232, 1985. SIGNIFICANT AREAS of viable myocardium often are dependent on coronary collateral channels for blood supply when advanced occlusive coronary artery disease is present. During periods of coronary spasm or acute occlusion of a major coronary artery, the degree of myocardial ischemia that develops is dependent in part on the availability of coronary collateral channels and the rate at which these channels begin to function. A native and usually marginally functional collateral circulation exists in both dogs and humans. Collateral channels develop rapidly after an appropriate stimulus in dogs, but do not become as functional as native arteries until approximately 6 months; thus, during development they are characterized as immature. Studies in which Khouri et al.' measured coronary pressure in dogs suggested that previously wellformed collateral channels may open gradually. From the Department of Medicine, Division of Cardiology, Duke University Medical Center, and the Medical Service, Cardiology Section, Veterans Administration Medical Center, Durham. This study was supported in part by the National Institutes of Health grant HL 18468 and the Medical Research Service of the Veterans Administration. Address for correspondence: Joseph C. Greenfield, Jr., M.D., Box 3246, Duke University Medical Center, Durham, NC 27710. Received Feb. 5, 1985; revision accepted April 11, 1985. Vol. 72, No. 1, July 1985 Greenfield et al.2 observed in patients undergoing coronary artery bypass surgery that reactive hyperemia was present after an acute 10 sec interruption of flow in the vein graft. However, reactive hyperemia largely disappeared if the occlusion was maintained for up to 1 min. This observation suggests that existing collateral channels may not fully open immediately after an acute interruption of antegrade blood flow but may begin to function over several minutes. Brazzamano et al.3 observed in dogs that when immature collaterals were present, repeated coronary artery occlusions of 5 min duration augmented collateral flow above that during the initial coronary occlusion. The purpose of the present study was to determine the rapidity with which immature coronary collateral channels begin to function during a brief occlusion of a major coronary artery. An awake animal preparation was used in which coronary collateral development had been stimulated by the placement of a partial stenosis on the left circumflex coronary artery. In this preparation a region of myocardium was perfused by both the partially stenosed circumflex coronary artery and from immature but developing coronary collateral channels. The change of the pressure drop across the 225 by gest on A ril 9, 2017 http://ciajournals.org/ D ow nladed from