Form 'fruste' of long QT syndrome as a possible cause for unexplained syncope revealed by dobutamine infusion.

摘要

The long QT syndrome is a genetically transmitted disorder characterized by prolonged ventricular repolarisa-tion that predisposes to malignant ventricular tachyarrhythmias. Recently, induction of torsades de pointes by dobutamine infusion was reported in a young girl with idiopathic long QT syndrome suggesting that adrenergic stimulation by dobutamine could induce dangerous arrhythmias in high risk patients.We here report a subgroup of 7 patients with unexplained syncope in whom a dobutamine stress echocardiography (performed because of an incomplete treadmill test) unexpectedly prolonged the QTc interval suggesting a possible form fruste of long QT syndrome as a cause for syncope. There were 3 men and 4 women, aged 38-72 years (54.8 +-11.5) without electrolyte disturbances. Six patients had a sudden syncope including 3 females treated with a known QT-prolong-ing drug removed several days before investigations (sotalol, venlafaxinum, amitriptyline). Baseline QT interval (32CM50 ms; mean: 397 +-27 ms)was considered normal but QTc (450-480 ms; mean: 465 + 7 ms) was slightly prolonged. During dobutamine stress echocardiography, mean QT interval was shortened to 342 + 25 ms (mean shortening: 54 + 22 ms as compared to baseline values; /> r< 0.02) but QTc interval was pro-longed to 545 +-7 ms (mean prolongation: 80 +-11 ms; /j:<0.002) without any induced ventricular arrhythmia or ischemia (Figs. 1 and 2, Table 1). Return to baseline QTc interval values was confirmed after dobutamine infusion was stopped. No specific treatment was proposed but advice was given to avoid all QT-prolonging drugs. During a follow-up period of 19.2 +-6.3 months, one patient suffered a new episode of syncope allocated to seizure disorders; analysis of his implanted loop recorder did not reveal any rhythm disturbance during syncope.