Noninvasive assessment of coronary stenoses by myocardial perfusion imaging during pharmacologie coronary vasodilatation: I. Physiologic basis and experimental validation

• Published in: The American journal of cardiology Vol. 41; no. 2; pp. 267 - 278
• Main Author: Gould, K.Lance
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1978
• ISSN: 0002-9149; 1879-1913
• DOI: 10.1016/0002-9149(78)90165-0

This study was undertaken to establish the basic hemodynamic conditions necessary to cause abnormalities in external myocardial perfusion images of thallium-201 and technetium-99M-labeled particles as a result of defined coronary stenoses ranging from mild to severe narrowing. Twenty dogs underwent long-term instrumentation with a flow transducer and adjustable constrictor on the left circumflex coronary artery. Catheters were implanted in the aortic root and distal left circumflex coronary artery to measure pressure loss across the stenosis and in the pulmonary artery and left atrium for the injection of drugs or radionuclides, or both. All data were obtained in intact unsedated trained animals. The results from 145 images obtained at rest, during exercise or after coronary vasodilators in dogs with mild to severe coronary stenoses demonstrate the following: (1) The ratio of maximal flow in a normal to stenotic coronary artery must be at least 2:1 before defects appear in the myocardial perfusion image of thallium-201. (2) A diagnostic technique that utilizes a maximal stimulus for increasing coronary flow and an imaging agent that is distributed to the myocardium in linear proportion to coronary flow at flow rates up to 4 or 5 times resting levels will be the most sensitive method for detecting mild coronary stenoses; a diagnostic technique utilizing a submaximal stimulus for coronary flow or an imaging agent whose distribution is not proportional to flow at high flow rates will be least sensitive. (3) Myocardial perfusion imaging during coronary vasodilatation induced with intravenously administered dipyridamole is a better method for identifying moderate coronary stenoses than perfusion imaging during exercise stress in experimental animals. (4) The effect of intravenously administered dipyridamole on the coronary circulation can be closely regulated by adjusting the dose rate of infusion and can be instantaneously reversed with intravenous administration of aminophylline, a dipyridamole antagonist; dipyridamole infusion does not increase myocardial oxygen demands as much as exercise and does not Invoke myocardial ischemia as a diagnostic end point. This stimulus may therefore be more readily controlled than exercise stress and is not subject to the effects on treadmill testing of motivation, chronic lung disease, peripheral vascular disease or musculoskeletal impairment.