Prominent positive U waves appearing with high-dose intravenous phenylephrine

A 71-year-old woman who had critical cerebral ischemia secondary to a carotid artery occlusion was receiving high-dose intravenous phenylephrine for a trial of hypertensive therapy. While on a maximal dose of phenylephrine she developed prominent positive U waves, which disappeared with the cessation of the drug. The possible underlying electrophysiological mechanisms of this phenomenon are discussed in this paper.