Hypopotassemia-induced U wave in electrocardiogram (an experimental study for possible mechanism)

Summary

To define the mechanism of hypopotassemia-induced U wave change, we performed open-chest experiments in 20 dogs and obtained following results: (1) During hemodialysis U wave amplitude of epicardial electrogram increased significantly (p<0.05) from 0.4±0.3 (mean ± SD) to 1.2±0.5 mV with lowering serum potassium (K) concentrations from 3.4±0.4 to 2.2±0.2 mEq/l (p<0.001) in 6 dogs. (2) These hypopotassemia-induced U waves disappeared after instillation of high K⁺ solution into the regional coronary artery, without detectable increase in systemic plasma K⁺ concentration. (3) In 10 dogs, huge (0.5–1.0 mV), delayed (corrected Q-U apex=0.66±0.16) positive U waves were induced at the epicardial surface by infusion of K⁺-free, Ca⁺⁺-rich Tyrode solution into the regional coronary artery, whereas no appearance of negative U waves was shown at the endocardial surface. (4) In all of 6 dogs with infusion of K⁺-free, Ca⁺⁺-rich solution, monophasic action potential registered with suction electrode showed early afterhyperpolarization, which corresponded to appearance of huge positive U waves. These data indicate that hypopotassemia-induced U wave may reflect early afterhyperpolarization developed in the ventricular muscle.