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REVIEW ARTICLE

Ventricular repolarization components on the electrocardiogram

Cellular basis and clinical significance

^* Main Line Health Heart Center, Wynnewood, Pennsylvania, USA

Manuscript received December 18, 2002; accepted April 30, 2003.

^* Reprint requests and correspondence: Dr. Gan-Xin Yan, Main Line Health Heart Center, 100 Lancaster Avenue, Wynnewood, Pennsylvania 19096, USA.
yanganxin{at}cs.com

Ventricular repolarization components on the surface electrocardiogram (ECG) include J (Osborn) waves, ST-segments, and T- and U-waves, which dynamically change in morphology under various pathophysiologic conditions and play an important role in the development of ventricular arrhythmias. Our primary objective in this review is to identify the ionic and cellular basis for ventricular repolarization components on the body surface ECG under normal and pathologic conditions, including a discussion of their clinical significance. A specific attempt to combine typical clinical ECG tracings with transmembrane electrical recordings is made to illustrate their logical linkage. A transmural voltage gradient during initial ventricular repolarization, which results from the presence of a prominent transient outward K⁺ current (I_to)-mediated action potential (AP) notch in the epicardium, but not endocardium, manifests as a J-wave on the ECG. The J-wave is associated with the early repolarization syndrome and Brugada syndrome. ST-segment elevation, as seen in Brugada syndrome and acute myocardial ischemia, cannot be fully explained by using the classic concept of an "injury current" that flows from injured to uninjured myocardium. Rather, ST-segment elevation may be largely secondary to a loss of the AP dome in the epicardium, but not endocardium. The T-wave is a symbol of transmural dispersion of repolarization. The R-on-T phenomenon (an extrasystole originating on the T-wave of a preceding ventricular beat) is probably due to transmural propagation of phase 2 re-entry or phase 2 early afterdepolarization that could potentially initiate polymorphic ventricular tachycardia or fibrillation.

Abbreviations and Acronyms   AP   action potential   APD   action potential duration   EAD   early afterdepolarization   ICa   L-type calcium current   IKr   rapidly activating delayed rectifier potassium current   IKs   slowly activating delayed rectifier potassium current   INa   inward sodium current   Ito   transient outward K+ current   LQTS   long QT syndrome   TDR   transmural dispersion of repolarization   VF   ventricular fibrillation   VT   ventricular tachycardia

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