THE SIGNIFICANCE OF THE T WAVE IN THE ELECTROGRAM AND ELECTROCARDIOGRAM

Abstract

The early history of the recognition of this wave and its presence in the electrical record of different invertebrates and vertebrates are discussed. A summary of current conceptions of the electrical state of resting and active tissue is given in order to understand the ultimate genesis of deflections like the T wave. For the same reason, the duration and appearance of the electrical changes recorded directly from a single region of the heart, the so-called mono-phasic action current, is described and its significance discussed. The view is presented, and the evidence pro and con discussed, that the T wave is the algebraic resultant of the last portion of the monophasic action currents recordable under each electrode, its contour being determined by the differences in the time of onset and in the duration of the monophasic action current in the two regions. The differences between the electrogram and electrocardiogram is discussed. Evidence is given to show that the heart during activity creates around itself an electrical field varying from moment to moment, which is tapped by the galvanometer to give the electrocardiogram. The 2 theories advanced to explain the production of the electrical field are discussed. The view is supported that at the time that the T wave is inscribed, the mechanism causing the electrical field is the presence of "distributed potential differences." These unbalanced electrical stresses are ascribed to differences in the time of onset and in the duration of activity in various fractions of the heart: the T wave is caused by this unbalancing of the electrical stresses. The temporal and causal relationship of the T wave to the mechanical and chemical phenomena is discussed. Similarly the relation of the end of the refractory phase to the T wave is analyzed and some new evidence given to show that in the entire heart a new beat may arise before the previous T wave is complete. In the clinical discussion the appearance of the T wave in different age groups is presented. The incidence and meaning of inverted T waves is analyzed. It is maintained that an inverted T wave is not pathognomonic of any clinical entity, nor can it be used to give a prognosis in individual cases, but it is rather to be regarded as a result of persistence of activity somewhere in the apical region of the heart unless its cause is a shifted anatomical axis or some extra-cardiac peculiarity. The evidence for this, pro and con, is evaluated. An extensive organized bibliography of about 500 references is included.