Giant T waves and QT interval prolongation associated with guanfacine toxicity.

Introduction: Guanfacine is a central α-adrenergic receptor agonist that produces drowsiness, bradycardia, hypotension, and occasionally QT interval prolongation. We discuss giant T waves associated with guanfacine toxicity.

Case Summaries: Three patients presented to the hospital with histories and physical findings compatible with guanfacine toxicity. Supratherapeutic concentrations were confirmed in two of them. All three developed QT interval prolongation and giant T waves on the electrocardiogram. Giant T waves occur commonly in patients with acute myocardial infarct and hyperkalemia, as well as rarely with a number of other cardiac and non-cardiac causes.

Conclusion: Guanfacine toxicity may cause the novel electrocardiographic finding of 'giant T wave with QT interval prolongation'. Further studies are warranted to investigate the association between the novel electrocardiographic finding and guanfacine toxicity, as well as its diagnostic utility in such cases.