Appraisal of Coronary Arteriography in Evaluating the Hemodynamic Significance of Experimental Coronary Artery Stenosis

Abstract

In vivo coronary arteriography has proved fairly reliable in localizing stenoses of the coronary arteries (8, 11, 12). However, many stenoses, even those appearing morphologically severe, may not be of hemodynamic significance, i.e., they may not decrease blood flow across, or pressure beyond, the stenosis. Heretofore, hemodynamic effects have been ascribed to coronary stenoses largely on the basis of clinical signs and symptoms and electrocardiographic abnormalities. This study was designed to assess the utility of coronary arteriography in appraising the hemodynamic significance of coronary artery stenoses. Method and Materials Varying degrees of concentric stenosis, about one millimeter in length, were produced in the circumflex artery of seven calves. Under general anesthesia, a left thoracotomy incision was made. A ligature was placed around the circumflex artery, and by adjusting its tension a stenosis of any desired degree could be produced. In all cases, pressures were continuously monitored through catheters in the aorta and in a small branch distal to the circumflex stenosis. Blood flow in the circumflex artery was intermittently monitored with a square wave electromagnetic flow-meter in 40 experiments on 5 calves. Selective right and/or left coronary arteriography was performed within minutes of production of all degrees of stenosis, and a total of 65 film sequences were obtained. Recording was on 16 mm cine film (mostly plus-X reversal) at 30 frames per second, and the system was capable of resolving over 32 line pairs per inch. At the conclusion of the study, the degree of constriction that resulted in the least detectable hemodynamic effect was reproduced, and an epoxy cast of this stenosis was obtained in 4 cases. The diameters and areas of such stenoses were then directly measured. Ciné arteriograms were examined at various frame rates, including frame-by-frame analysis. The diameter of the stenosis was measured in some cases with a low-power microscope. The following arterio-graphic parameters were correlated with pressure and flow determinations: 1. Diameter of the stenosis 2. Collateral flow 3. Decreased linear velocity of flow 4. Transient poststenotic dilution 5. Poststenotic narrowing. Luminal diameter of the stenosis was estimated from the cine arteriogram in terms of percentage of the prestenotic portion of the artery. Direct measurements, using microscopic examination of the film and adjustment with a known magnification factor, proved impractical because of the grain of the film and other limitations of resolution. Collateral flow was easily recognized, when opacified, since larger vessels could be seen filling from smaller ones.