Ischaemia-induced negative U waves in electrocardiograms (an experimental study in canine hearts).

To confirm the clinical impression that negative U waves are a sign of myocardial ischaemia, and to study their possible mechanism, we performed open chest experiments on dogs with the following results. (1) A negative U-wave tended to appear the peripheral rather than the central portion of the cyanotic zone following coronary artery occlusion; (2) it also appeared temporarily at the central ischaemic area after release of coronary artery occlusion; (3) it became apparent or accentuated with augmentation of left ventricular performance at a postextrasystolic beat; and (4) it was eliminated by infusion of K+-free Tyrode solution, but appeared after an infusion of high K+-Tyrode solution into the regional coronary artery. These results indicate that negative U waves are a sign of myocardial ischaemia, which may be related not only to simple myocardial stretching but also to contraction and external high K+ in the ischaemic area.