Genesis of the Electrocardiogram

Analysis of the Electrocardiographic Waveforms Produced by Right Ventricular Pacing: Relation to the Nonpaced Patterns

“…A limitation of estimating LV dimensions from the ECG is that a relatively small amount of the cardiac potentials generated from normal ventricular excitation is evident from measurements made external to the heart 1 . Normal His‐Purkinje excitation, with its extensive multidirectional spread, results in a substantial loss of the resultant potential by cancellation of directionally opposite electrical forces 7 . Estimates of the LV thickness (or mass) based on regression analyses using QRS complex amplitude measured during normal ventricular conduction would not be expected to apply to those resulting from aberrant conduction, with reduced His‐Purkinje activation and presumably less cancellation.…”

Is there a significant transmural gradient in repolarization time in the intact heart?

“…In modern textbooks, there are diagrams depicting action potentials at the endocardium and the epicardium, where repolarization occurs earlier at the epicardium. 5,6 To quote Mirvis and Goldberger 7 : ". .…”

“…in the normal heart, the forces of depolarization and repolarization are usually oriented in the same direction on the ECG recording." Thus, as is evident from the textbooks, [5][6][7][8] there appears to be a consensus that transmural gradients in activation and repolarization are opposite. This concept is primarily based on the work of Antzelevitch and colleagues 9,10 on the isolated, arterially perfused canine wedge preparation.…”

“…The overlap of the ranges of repolarization time in RV and LV is considerable. In both ventricles, the dispersion of repolarization times along the endocardium and epicardium was substantially larger than the transmural dispersion, and the notion from textbooks that epicardial repolarization precedes endocardial repolarization [5][6][7][8] could not be confirmed.…”

A Review of Fetal ECG Signal Processing Issues and Promising Directions

“…In some measurements the T-wave is followed by a small wave known as the U-wave, which for normal ECG, is believed to be due to repolarization of the His-Purkinje system [37]. Other hypotheses for the origin of the U-wave have been suggested in [39]. The segment between the end of the U-wave up-to the beginning of the next P-wave is known as the isoelectric segment of the ECG, in which the myocardium does not have a measurable activity.…”