QT interval variability in panic disorder patients after isoproterenol infusions

Anxiety symptoms are associated with a marked increase in sudden cardiac de ath, suggesting an abnormality in the autonomic control of the heart. We ex amined the effects of sympathetic stimulation on QT interval variability in panic disorder patients by infusing the P-adrenergic agonist isoproterenol in 6 panic disorder patients and II normal subjects. The ECG signal was an alysed before the infusion and after 5 min after the infusion was started. The outcome measures were the QT variability normalized for mean QT interva l (QTvm) and the QT variability index (QTvi), a measure of QT variability n ormalized by the concomitant heart rate variability. Patients with panic di sorder had more variability in QT interval duration than normal controls an d this variability was increased further by sympathetic stimulation with is oproterenol. The isoproferenol-associated increase in QT interval occurred in controls in the absence of significant anxiety. However, on one of two m easures, the increase in QT interval variability was greater in patients wi th panic disorder, suggesting a greater sensitivity to isoproterenol or to isoproterenol-induced anxiety.