U wave inversion.

The U wave, when first recognized by Einthoven (1906) in the earliest days of electrocardiography, was considered by him to be pathological. Since then the normality of upright U waves, except perhaps in cases where they are unusually high (Katz, 1946), has been generally conceded. Various hypotheses have been advanced to explain the U wave, of which the most satisfactory is that of Hoff and Nahum (1938) who concluded on experimental grounds that it undoubtedly forms part of the ventricular complex, and is coincident in time with the supernormal phase. The number of papers on the clinical significance ofthe U wave is small, and reflects the scant attention that seems to have been paid to it by most cardiologists. Important articles however are those of Nahum and Hoff (1939), Papp (1940), and Solarz and Elek (1943), and to them the reader is referred for comprehensive reviews of the subject. Inversion of U has been considered pathological by most authors. Nahum and Hoff found it in association with coronary, rheumatic, hypertensive, and pulmonary heart disease. Papp reported it in coronary disease and in hypertension. Solarz and Elek found 94 cases of U wave inversion in 1000 cases studied; they report on its association with the left heart strain pattern, intraventricular block, and anterior and posterior wall infarction.