The electrocardiographic T-wave is mainly explained by temporal repolarization differences along various anatomical axes

Purpose: T-wave abnormalities are used to identify risk for life-threatening arrhythmias. However, the exact genesis of the T-wave is still unclear. Therefore, we conducted an experimental study to correlate the ventricular repolarization pattern derived from intramural electrograms with the corresponding T-wave on the surface map. Methods: Pig hearts (n=9) were perfused according to Langendorff and paced from the atrium (cycle length 650 ms). Transmural needles (32-45 needles, 4 electrode terminals each) were inserted and local activation and repolarization times (AT and RT) were derived from unipolar electrograms. RT differences (maximum minus minimum) were determined along 4 anatomical axes: LV apico-basal, LV anterior-posterior, left-right ventricle and LV transmural. The hearts were immersed in a blood-filled container with 61 electrodes. From the simultaneously recorded electrograms, a pseudo body surface map (BSM) was derived. From the BSM the maximum T-wave duration was determined using the tangent method in the pseudo ECG with the largest T-wave amplitude. Results: Activation occurred earliest at the septum and latest at RV basal free wall and outflow tract, as in the human heart. Transmural activation was almost simultaneous, due to the transmural Purkinje network in the porcine heart. The T-wave in the body surface electrograms had a maximum duration of 93±4 ms (mean ± sem, n=9). In general, repolarization started at the septum and terminated at the left (LV) and right (RV) free walls. The maximum absolute temporal RT differences were: LV apico-basal (51±6 ms, n=9), LV anterior-posterior (51±9 ms, n=9) and between LV and RV (66±6 ms, n=9). The maximum absolute transmural RT difference in the LV was 34±7 ms (n=9). Latest minus earliest moment of repolarization within the hearts was 73±6 ms independent of axes. T-wave onset was always earlier (20±6 ms) than the minimum repolarization moment. T-wave end was similar to the maximum repolarization moment (0±3 ms). Conclusions: The major part of the electrocardiographic T-wave is explained by temporal repolarization differences across the entire heart, and not by only left-right, LV anterior-posterior, LV apico-basal or LV transmural RT differences. The discrepancy between T-wave onset and earliest RT may be explained by differences in action potential morphology.