The Field Function on the Body Surface during Moments in the U Wave in Normal Subjects and in Patients with Cardiac Pathology ‡

Attention to the U wave is practically nonexistent among clinical electrocardiographers. Nevertheless, this wave exists, is most frequently found in the precordial leads and less often in the limb leads. Characteristically, when the U wave is present, its direction is generally the same as that of the T wave which it follows. Its greatest amplitude seems to be found in V2-V4 or 5, and then it declines and disappears in V6 and V7. In rare instances an inverted U in the precordial leads may be the only evidence in the electrocardiogram of the existence of heart disease. There are times when it falls on the downstroke of T, while at other times it appears in a diphasic terminal portion of T. In practically all observations thus far made it was found in a fixed time relationship with Q.6 It cannot be assumed that because U is in a fixed time relationship with Q, the QU interval is a measure of the refractory period of the ventricle. In the intact dog heart, the basal fibers of the left ventricle were found to emerge from the refractory period last, and this moment corresponded with the end of T in the precordial electrocardiogram. The refractory period was never found to extend to where U would terminate.5 We must therefore recognize that U is independent of the refractory period, and this makes it necessary to seek for its explanation in electrical events in excitable tissue that occur after the refractory period. That such a phenomenon exists can be seen in the work of Erlanger and Gasser, who have shown both negative and positive after-potentials long after the period of excitation accompanying the propagation of the nerve impulse. Such after-potentials seem to be associated with various phases of recovery and are profoundly influenced by metabolic mechanisms affecting recovery. Many of the speculations offered to explain the origin of the U wave invoke an extracardiac as well as cardiac origin. In general most observers