other versions

abstract in J. Electrocardiol. 40 Suppl. (2007) page S49

conference proceedings paper in Anatol. J. Cardiol. 7 Suppl 1 (2007) pp 164-167 (poor graphics)

manuscript for conference paper (with better graphics)

context

This conference paper is the first demonstration in a complete 3-D heart model that repolarization time, defined as the instant of fastest downstroke of the action potential, coincides with the instant of fastest upstroke of the local electrogram. It also describes a preliminary version of a simple model for the local electrogram, a rule-of-thumb model intended to help understanding this relation intuitively. An improved version of the simple model was published later in Am. J. Physiol. H.

abstract

introduction  As a measure of repolarization time (Tr), the instant of maximum slope (Tu) of the T wave in the local unipolar electrocardiogram is commonly used. Although this method has been well established both theoretically and experimentally, recent observations on positive T waves in human hearts have caused a renewed debate, involving also the theoretical basis for the use of Tu. The purpose of this study was (1) to elucidate the mechanism that leads to positive and negative T waves and (2) to investigate theoretically which electrocardiogram feature best predicts Tr.

methods  We used a bidomain reaction-diffusion model of the human heart with anisotropic myocardium, transmural fiber rotation, and heterogeneous ion-channel properties. This model calculates both propagating action potentials (AP) and electrocardiograms. To explain positive T waves, we compared results with those of a much simpler model, which predicts T waves from local and remote AP. We simulated normal tissue, repolarization abnormalities and fibrotic tissue.

results  Repolarization time was defined as the instant of steepest downstroke of the AP. The sign of the T wave was almost uniquely determined by Tr. Positive T waves occurred at early-repolarizing sites. In healthy tissue, the 2 models agreed on T-wave sign in 92% of sites and predicted similar T waves. This demonstrates that T-wave shape is determined primarily by the difference between the local AP and the average AP in the ventricles. Correlation between Tu and Tr was above 0.99 in both negative and positive T waves.

conclusions  Our study predicts that (1) The sign of the T wave is primarily determined by the difference between local AP and the average AP in the ventricles; (2) positive T waves occur at earlyrepolarizing sites; (3) Local Tr is best estimated by Tu, also in positive T waves; and 4) scarring and fibrosis may preclude any repolarization measurement.

funding

Computational resources for this work were provided by the Réseau québécois de calcul de haute performance (RQCHP). M. Potse was supported by a postdoctoral research award from the Groupe de recherche en sciences et technologie biomédicale (GRSTB), École Polytechnique and Université de Montréal; and by the Research Center of Sacré-Coeur Hospital, Montréal, Québec, Canada.