Published Online
on April 21, 2003

A more recent version of this article appeared on May 6, 2003

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Submitted on November 21, 2002
Revised on January 31, 2003
Accepted on February 4, 2003

Imaging Electrocardiographic Dispersion of Depolarization and Repolarization During Ischemia. Simultaneous Body Surface and Epicardial Mapping

Martyn P. Nash PhD^*, Chris P. Bradley PhD, and David J. Paterson DPhil

From the University Laboratory of Physiology, University of Oxford, Oxford, UK.

^* To whom correspondence should be addressed. E-mail: martyn.nash{at}auckland.ac.nz.

Background--Myocardial ischemia creates abnormal electrophysiological substrates that result in life-threatening ventricular arrhythmias. Identifying patients at risk of such abnormalities by use of body surface electrical measures is controversial. We investigated the sensitivity of torso measures, recorded simultaneously with epicardial electrograms, to changes in dispersion of depolarization and repolarization during localized ventricular ischemia.

Methods and Results--Ventricular epicardial electrograms were recorded from 5 anesthetized pigs with a 127-electrode sock. A controllable suture snare was used to ligate the left anterior descending coronary artery (LAD). The chest was reclosed, and a vest with 256 ECG electrodes was fitted to the torso. Simultaneous arrays of epicardial electrograms and torso ECGs were recorded during LAD occlusion and reperfusion. Activation-recovery intervals (ARIs), QT_u and RT_u dispersion (where u indicates upstroke), and QRST integrals were calculated, and these data were fitted to anatomically customized computational models of the swine ventricular epicardium and torso. LAD occlusion caused the epicardial ARI dispersion to steadily increase, whereas the location of shortest ARI shifted from the posterobasal ventricular tissue (control) to the anteroapical myocardium, distal to the suture snare. These changes were associated with a steady increase in the torso RT_u dispersion as the shortest RT_u interval moved from the right shoulder (control) to the sternum. QT_u and RT_u dispersion determined from the 12-lead ECG did not consistently reflect the myocardial changes.

Conclusions--Although changes in myocardial repolarization dispersion resulting from localized ischemia are not reliably reflected in temporal indices derived from the 12-lead ECG, they can be readily identified with high-resolution torso ECG mapping.

Key words: electrocardiography • ischemia • mapping • potentials • repolarization

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