Pathophysiology and Natural History Coronary Artery Disease

To determine the effect of atherosclerotic coronary lesions on myocardial blood flow in patients at rest, regional myocardial blood flow was measured distal to stenotic lesions in 29 patients with isolated proximal lesions of the left anterior descending artery. Severity of coronary stenosis was measured by computer-assisted cinevideodensitometric analysis of digitized coronary arteriograms. Regional myocardial blood flow was measured from the clearance rate of intracoronary 133Xe injected into the left main coronary artery and recorded with a multicrystal scintillation camera. In 21 patients with stenotic lesions ranging from 19% to 84% area reduction, distal regional myocardial blood flow was normal. In all eight patients with reduced regional myocardial blood flow distal to left anterior descending lesions, the minimum area of each stenotic lesion was less than 0.80 mm2 (mean 0.34 + 0.2 mm2). minimum calculated diameter was less than 1 mm (mean 0.59 + 0.3 mm), and percent stenosis, based on the reduction in cross-sectional area, was greater than 85% (mean 94 + 4%). For all patients, distal flow, expressed as a fraction of normal flow, correlated with the lesion cross-sectional area (r = .84), minimum luminal diameter (r = .84), and percent area stenosis (r = -.70). Thus, resting myocardial blood flow distal to stenotic lesions of the proximal coronary arteries remains normal until the degree of narrowing is severe. The dimensions observed for critical coronary stenotic lesions correlate well with theoretical predictions based on fluid mechanics and with experimental preparations in laboratory animals. Circulation 74, No. 4, 746-757, 1986. CRITICAL STENOSIS is generally defined as that degree of stenosis for which a small further reduction in luminal area will cause significantly reduced blood flow distally.1 Numerous experimental studies in canine preparations of the relationship between regional myocardial blood flow and severity of coronary arterial stenosis have shown that, as an artery is gradually constricted, distal flow remains normal until a critical degree of stenosis is reached.24 Typically, the luminal area must be severely reduced before distal flow falls. Flow is maintained at normal levels, until the stenosis is severe, by autoregulatory vasodilation of the distal vascular bed.6 7 Peripheral vasodilation lowers arterial pressure distal to the lesion and thus widens the pressure drop across the stenosis. This increased pressure gradient enhances the driving pressure, which maintains flow at normal or near-normal levels. From the Departments of Medicine and Radiology, College of Physicians and Surgeons, Columbia University, New York. Supported by USPHS grants HL-32906 and HL-14148. Address for correspondence: Allen B. Nichols, M.D., Cardiovascular Laboratory, Presbyterian Hospital, 622 West 168 St., New York, NY 10032. Received Feb. 12, 1986; revision accepted June 25, 1986. Presented in part at the Annual Scientific Session of the American Heart Association. 746 Studies in canine preparations have consistently reported values of approximately 80% to 95% reduction in luminal area as the critical stenosis causing reduced blood flow under resting conditions.2 5 Of the many geometric and rheologic variables that affect blood flow through a stenosis, the most important variable is the ratio of the minimum cross-sectional area of the stenosis to the unobstructed luminal area.' This ratio is commonly expressed as percent stenosis and calculated as (1 -As/An) x 100. The degree of coronary stenosis that reduces regional myocardial blood flow in patients at rest has never been determined, largely because techniques for measuring regional myocardial blood flow and magnitude of coronary stenosis have been imprecise. Recently we have developed a method for quantifying coronary stenosis based on computer-assisted videodensitometric analysis of the radiographic density of intra-arterial contrast medium.8 This method for calculating percent stenosis is based on relative luminal areas and has been validated in both phantom and postmortem heart studies. We used this technique to measure the dimensions of coronary stenotic lesions in 29 patients with isolated CIRCULATION by gest on A ril 4, 2017 http://ciajournals.org/ D ow nladed from PATHOPHYSIOLOGY AND NATURAL HISTORY-CORONARY ARTERY DISEASE proximal lesions of the left anterior descending (LAD) artery. Regional myocardial blood flow distal to each stenosis was measured scintigraphically from the clearance rate of intracoronary 133Xe and was related to the degree of stenosis to define critical coronary stenosis in patients under resting conditions. The objective of this study was to determine the critical degree of stenosis that causes distal coronary blood flow to fall in patients with coronary artery disease.