Published online before print September 12, 2005, doi: 10.1161/CIRCULATIONAHA.104.516583
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(Circulation. 2005;112:1711-1718.)
© 2005 American Heart Association, Inc.
Arrhythmia/Electrophysiology |
Repolarization Gradients in the Canine Left Ventricle Before and After Induction of Short-Term Cardiac Memory
From the Center for Molecular Therapeutics (M.J.J., E.A.S., E.P.A., A.N.P., I.N.S., P.D., M.R.R.), Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York; the Experimental and Molecular Cardiology Group (R.C., J.M.T.d.B., M.J.J., T.O., J.G.P.T.), Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands; and the Department of Medical Physiology (T.O.), University of Utrecht, and the Interuniversity Cardiology Institute of the Netherlands (J.M.T.d.B.), Utrecht, the Netherlands.
Correspondence to Michiel J. Janse, Experimental and Molecular Cardiology Group, Academic Medical Center, M052, Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands. E-mail m.j.janse{at}amc.uva.nl
Received October 25, 2004; revision received June 24, 2005; accepted July 1, 2005.
Background— Questions remain about the contributions of transmural versus apicobasal repolarization gradients to the configuration of the T wave in control settings and after the induction of short-term cardiac memory.
Methods and Results— Short-term cardiac memory is seen as T-wave changes induced by altered ventricular activation that persists after restoration of sinus rhythm. We studied cardiac memory in anesthetized, open-chest dogs paced from the ventricle for 2 hours. Unipolar electrograms were recorded from as many as 98 epicardial and 144 intramural sites, and activation times and activation-recovery intervals (ARIs) were measured. In separate experiments, epicardial monophasic action potentials were recorded. We found no appreciable left ventricular intramural gradients in repolarization times (activation time+ARI) in either control conditions or after the induction of memory. In controls, there was a left ventricular apicobasal gradient, with the shortest repolarization times in anterobasal regions and longest repolarization times posteroapically. After induction of memory, repolarization times shortened uniformly throughout the ventricular wall. Monophasic action potential duration at 90% repolarization decreased by 
10 ms after induction of memory.
Conclusions— In the intact canine left ventricle at physiological rates, there is no transmural gradient in repolarization. Apicobasal gradients in repolarization time, with shortest repolarization times in anterobasal areas and longest repolarization times in posteroapical regions, are important in the genesis of the T wave. Repolarization times and monophasic action potentials at the 90% repolarization level shorten after the induction of memory. The deeper T wave in the ECG after induction of memory may be explained by the more rapid phase 3 of the action potential.
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