Precordial and Epicardial Surface Potentials during Myocardial Ischemia in the Pig

The solid angle theorem was used to analyze the relationships between TQ and ST segment deflections recorded from precordial and epicardial locations and the time course, size, shape, and transmural location of the ischemic process in the ventricular myocardium. Mathematical predictions were compared with experimental data from the intact heart. Precordial electrograms obtained in anesthetized close-chest pigs were compared with epicardial electrograms recorded directly from the heart's surface. Various areas of ischemia were produced by occluding large and small coronary artery branches, and the resultant changes in ischemic shape were delineated with Thioflavin S injections and postmortem ultraviolet photography. Formally derived equations and cumulative experimental data were in close agreement, suggesting that in the ischemic ventricle (1) TQ depression always accompanies ST elevation, (2) TQ and ST segment changes in magnitude and polarity are complex functions of ischemic size, shape, and transmural location; (3) precordial electrocardiogram (ECG) ST segment elevation is directly related to ischemic size; and (4) epicardial ECG ST segment elevation is inversely related to ischemic size. It is thus concluded that precordial and epicardial ECG TQ and ST segment deflections are complex functions of ischemic geometry and that their accurate interpretation with respect to ischemic size and shape and in the presence of pharmacological interventions is often difficult and may be misleading. • In 1920 Pardee (1) demonstrated that ST segment changes in the peripheral electrocardiogram (ECG) are indicative of myocardial injury in a patient with coronary heart disease. Later Wilson et al. (2) placed an electrode on the epicardial surface of the dog heart and confirmed that ST segment alterations occur with coronary artery ligation. More recently, the epicardial surface electrogram has had wide application in a variety of experimental situations designed both to confirm and to quantify regional myocardial ischemia (3). In all of these studies, the unproven assumption has been made that previous clinically and empirically derived relationships between alterations in the ST segment of the precordial electrogram and the presence, duration, size, and configuration of the ischemic process in the ventricular wall are equally applicable to interpretation of similar From the Experimental Hemodynamics Laboratory, Department of Medicine-Cardiology, University of Chicago Pritzker School of Medicine, Chicago, Illinois 60637. This work was supported by U. S. Public Health Service Grants HL 4368133 and HL 70-132-02 from the National Heart and Lung Institute, by The Louis Block Fund, and by Sinton Charitable Associates of the University of Chicago. This article was awarded first prize in the Young Investigator competition of the Chicago Society of Internal Medicine, April, 1975. Received November 18, 1974. Accepted for publication July 18, 1975. Circulation Research, Vol. 37, October 1975 changes recorded from the epicardial surface of the