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(Circulation. 2001;104:1299.)
© 2001 American Heart Association, Inc.

Basic Science Reports

Imaging Dispersion of Myocardial Repolarization, I

Comparison of Body-Surface and Epicardial Measures

John E. Burnes, PhD; Raja N. Ghanem, MS; Albert L. Waldo, MD; Yoram Rudy, PhD

From the Cardiac Bioelectricity Research and Training Center, Department of Biomedical Engineering, and Department of Medicine, Case Western Reserve University, and University Hospitals of Cleveland, Cleveland, Ohio.

Correspondence to Yoram Rudy, Director, Cardiac Bioelectricity Center, 509 Wickenden Bldg, Case Western Reserve University, Cleveland, OH 44106-7207. E-mail yxr{at}po.cwru.edu

Background— Body-surface ECG measures (QT dispersion [QTd], QRST integrals) have been used as indices of myocardial repolarization abnormalities with the goal of identifying patients at risk of fatal arrhythmias. The clinical utility of these measures has been questioned. We investigate the complex relationship between epicardial and body-surface potentials in the context of regionally abnormal myocardial repolarization.

Methods and Results— Epicardial potentials were recorded with a 224-electrode sock from an open-chest dog during control, regional epicardial warming, cooling, and adjacent warming and cooling to induce localized alterations in myocardial repolarization and regions of increased repolarization dispersion. Body-surface potentials were generated from these epicardial potentials in a human torso model. Epicardial estimates of repolarization (activation recovery intervals [ARIs] and QRST integrals) were evaluated for their ability to identify regions with increased repolarization dispersion. Body-surface QRST integrals and QTd in 12-lead ECG and 64-lead body-surface potential maps were evaluated for their ability to detect increased dispersion of myocardial repolarization. Epicardial ARI and QRST integral maps successfully located epicardial regions with increased dispersion of repolarization. The increased dispersion was not consistently reflected in the 12-lead or 64-lead ECG QTd or in the body-surface QRST integral maps.

Conclusions— This study demonstrates the inadequacy of body-surface measures that are thought to reflect myocardial dispersion of repolarization. In contrast, measures based on epicardial electrograms (ARI or epicardial QRST integral maps) provide physiologically relevant information about myocardial repolarization and can locate regions of increased dispersion.

Key Words: arrhythmia • electrocardiography • electrophysiology • imaging • potentials

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