The Role of Transmural Repolarization Gradient in the Inversion of Cardiac Electric Field: Model Study of ECG in Hypothermia.

BACKGROUND: The changes in ventricular repolarization gradients lead to significant alterations of the electrocardiographic body surface T waves up to the T wave inversion. However, the contribution of a specific gradient remains to be elucidated. The objective of the present investigation was to study the role of the transmural repolarization gradient in the inversion of the body surface T wave with a mathematical model of the hypothermia-induced changes of ventricular repolarization.
METHODS: By means of mathematical simulation, we set the hypothermic action potential duration (APD) distribution on the rabbit ventricular epicardium as it was previously experimentally documented. Then the parameters of the body surface potential distribution were tested with the introduction of different scenarios of the endocardial and epicardial APD behavior in hypothermia resulting in the unchanged, reversed or enlarged transmural repolarization gradient.
RESULTS: The reversal of epicardial repolarization gradients (apicobasal, anterior-posterior and interventricular) caused the inversion of the T waves regardless of the direction of the transmural repolarization gradient. However, the most realistic body surface potentials were obtained when the endocardial APDs were not changed under hypothermia while the epicardial APDs prolonged. This produced the reversed and increased transmural repolarization gradient in absolute magnitude. The body surface potentials simulated under the unchanged transmural gradient were reduced in comparison to those simulated under the reversed transmural gradient.
CONCLUSIONS: The simulations demonstrated that the transmural repolarization gradient did not play a crucial role in the cardiac electric field inversion under hypothermia, but its magnitude and direction contribute to the T wave amplitude.