II. Various Types of Fusion Between T and U Waves

Abstract

The term "superposition of T and U" is applied to patterns in which these waves are only partially merged and separated by a notch. The term "fusion of T and U" implies uniform monophasic or diphasic waves showing no landmarks for differentiation of their components. Monophasic fusion waves may have "equidominant T and U components" resulting in a single "summation apex"; in this case the upstroke of U is steeper than the downstroke of U is steeper than the downstroke of T. They may show "predominance of the T com- ponent", when their apex corresponds to that of T, or "predominance of the U component", when their apex corresponds to the apex of U. The latter type is often found in hypopotassemia. A "pseudofusion wave" may result if the T component is iso-electric. A table is presented which illustrates 48 types of fusion waves which can result from merging all possible con-figurations of T and U waves, and many of these are illustrated by clinical electrocardiograms. Uniform diphasic waves can also result without fusion, if a monophasic U begins immediately after the end of a monophasic T of opposite polarity; these waves are called "continuation waves". Differentiation of fusion and continuation waves from simple T waves is possible if the interval from Q to the end of the wave agrees with the Q-U interval predicted for heart rate; if a notch at the site where the T-U junction is expected is present in other complexes of the same lead or in other leads, or on other occasions; if this wave extends more than 0.04 seconds beyond the 2d heart sound; or if the components can be separated by administration of Ca or K.