NEWS AND VIEWS zyxwvu Edited by Peter A. McCullough Rationale and Methods for Assessment of Coronary Flow Prior to Coronary Intervention: Where Are We Headed? zyxw HANUMANTH zyxwvuts K. REDDY, M.D., SANTHOSH K.G. KOSHY, M.D., D.M., MICHAEL STUREK, PH.D., VINOD K. JAYAM, M.D., ASHWANI BEDI, M.D., and PETER A. MCCULLOUGH, M.D., M.P.H. zyx * From the University of Missouri-columbia School of Medicine, Department of Internal Medicine, Division of Cardiology, Dalton Cardiovascular Research Center, Columbia; and the *University of Missouri-Kansas City, School of Medicine, Deparhents of Basic Science and Internal Medicine, Cardiology Section, Truman Medical Center, Kansas City, Missouri Definition and Significance of Coronary Flow Reserve The human circulation to the human myocardium is unique in multiple ways. There is a great need for oxygenated blood supply to the myocardial muscle. The heart mainly operates on aerobic metabolism. Since the coronary arterial oxygen extraction is at near maximal level (coronary sinus oxygen saturation zyxwvu 25-35%),' myocardial blood flow and oxygenation are critically dependent on coronary vasodilator re- serve. Coronary flow reserve (CFR) is defined as the maximal extent of coronary flow relative to the base- line flow elicited by a potent pharmacological stimu- lus. CFR is a ratio of maximally elicited coronary flow to resting flow. It is 2-5 in humans and 4-7 in experimental animals. Coronary flow stimulators in- clude transient coronary occlusion, angiographic con- trast, intracoronary nitroglycerin, adenosine, bradykinin, and papaverine. CFR represents the max- imal vasodilator capacity of the total coronary vascu- lar bed largely comprising of the microvascular net- work and conduit epicardial vessels. CFR is inversely proportional to coronary microvascular resistance if the conduit vessels are normal. Coronary vascular re- sistance is coronary perfusion pressure divided by Address forreprints: Peter A. McCullough, M.D., M.P.H., F.A.C.C., F.A.C.P.. F.C.C.P., F.A.H.A., Division of Cardiology, William Beaumont Hospital, 3601 W. Thirteen Mile Road, Royal Oak, MI 48073. Fax: (248) 551-4199; e-mail: pmc975@yahoo.com coronary flow. The commonly occurring coronary stenoses can, therefore, interfere with CFR. In other words, CFR depends upon the integrity of the large and small coronary vessels. Determinants of Coronary Flow Reserve The myocardium has a unique supply and demand relationship facilitating an instantaneous increase (within a second) in coronary blood flow via a rapid re- duction in coronary vascular resistance in response to an increase in oxygen demand. This type of instanta- neous response is termed reactive hyperernia. Metabolic mediators of this reactive hyperemia in- clude adenosine, nitric oxide, vasodilator prostaglandins, partial pressures of oxygen and carbon dioxide, and adenosine triphosphate (ATP) sensitive K+ channels. Relation Between Stenoses and Flow In a given patient, CFR can be used to assess the physiological significance of (epicardial) coronary stenoses. CFR does not decline until the epicardial coronary diameter stenosis averages zyx 2 60%. At the epicardial diameter stenosis of approximately L 90%, CFR is usually completely depleted and the basal coronary flow begins to be compromised.* Vol. 15, No. 4,2002 Journal of Interventional Cardiology 335