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(Circulation. 2005;112:1085-1087.)
© 2005 American Heart Association, Inc.

Editorial

Stress Echo Without the Stress

Detection of Coronary Stenosis at Rest by Myocardial Contrast Echocardiography

Paul A. Grayburn, MD

From the Department of Internal Medicine, Division of Cardiology, Baylor University Medical Center, Dallas, Tex.

Correspondence to Paul A. Grayburn, MD, Baylor University Medical Center, Baylor Heart and Vascular Institute, 621 North Hall St, Suite H030, Dallas, TX 75226. E-mail paulgr@baylorhealth.edu

Key Words: Editorials • echocardiography • contrast media • coronary disease • microcirculation

An extract of the first 250 words of the full text is provided, because this article has no abstract.

	Introduction

 
Exercise or pharmacological stress has long been a mainstay of diagnostic testing aimed at identifying the presence of a flow-limiting coronary stenosis. The basis for this is the well-known clinical observation that even severe coronary artery atherosclerosis does not usually cause angina or ischemia at rest. Sir William Osler observed that angina pectoris is commonly precipitated by "muscular exertion, violent mental states, stomach upsets, or cold weather."¹ However, in Osler’s time, the mechanism whereby resting myocardial perfusion was maintained despite a hemodynamically significant coronary stenosis, namely coronary autoregulation, was unknown.

See p 1154

	Coronary Autoregulation

 
Myocardial oxygen consumption and perfusion are tightly coupled.² Because the myocardium extracts most of the oxygen delivered to it, increases in oxygen demand (eg, exercise, tachycardia) require a prompt increase in myocardial perfusion. For example, maximal exercise can easily cause a 4-fold increase in myocardial oxygen consumption, which is matched by a 4-fold increase in myocardial perfusion.³ Such hyperemic flow is typically mediated by vasodilation of precapillary arterioles to provide increased nutrient flow at the capillary level. Under normal conditions, 40% to 50% of total coronary resistance resides at the level of these precapillary arterioles (those <100 µm in diameter).^4,5 These vessels respond rapidly to complex neural and metabolic control mechanisms to maintain myocardial perfusion over a wide range of driving pressures, a process known as autoregulation.^6–8

Autoregulation is able to maintain nearly constant myocardial perfusion over a pressure range of 40 to 130 mm Hg in conscious dogs.⁹ A similar autoregulatory pressure range has been reported . . . [Full Text of this Article]

Related Article:

Detection of Coronary Stenoses at Rest With Myocardial Contrast Echocardiography

Kevin Wei, Khim Leng Tong, Todd Belcik, Patrick Rafter, Michael Ragosta, Xin-Qun Wang, and Sanjiv Kaul
Circulation 2005 112: 1154-1160. [Abstract] [Full Text]

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