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The ECG is one of the oldest and most versatile noninvasive cardiac diagnostic tests. It has remained in use essentially in its original form despite dramatic advances in cardiac electrophysiology. In May 1887, Augustus Desire Waller recorded the first human Electrogram using a primitive instrument called a Libbmann capillary electrometer. It had 2 deflections corresponding to ventricular depolarization and repolarization.1 In 1903, Willem Einthoven invented the String Galvanometer—a more sophisticated voltage recording instrument and recorded an Elektrokardiogramm with 5 deflections that he named PQRST.2  Since its initial invention, the body surface ECG has become a commonly used and extremely valuable test for the diagnosis of a variety of cardiac conditions. Despite a century of prolific use and intensive investigation, the cellular basis of ECG waveforms, particularly the T wave, remains a matter of debate.

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