The QT interval in drug-free depressed patients.

The QT interval is a noninvasive measurement obtained from electrocardiographic tracings. Long QT intervals occur in individuals at risk for fatal cardiac arrhythmias, and tricyclic antidepressant drugs can produce an increase in the QT interval. In this study, the authors compared the QT intervals from drug-free depressed patients, patients with substance use disorders, and normal control subjects. QT prolongation occurred more frequently (p less than .05) and severely (p less than .01) in the drug-free depressed subjects than in the controls. These results suggest that some drug-free depressed patients have increased QT intervals. These patients may be at risk for sudden, unexpected cardiac arrhythmias unrelated to the cardiotoxic effects of tricyclic antidepressant drugs.