Background: The long‐QT syndromes (LQTS) are inherited electrical cardiomyopathies characterized by prolonged ventricular repolarization and ventricular arrhythmias. Several genetic reports have associated defects in LQTS‐causing genes with atrial fibrillation (AF). We therefore studied whether atrial arrhythmias occur in patients with LQTS under daily‐life conditions.

Methods: We systematically assessed atrial arrhythmias in LQTS patients and matched controls using implanted defibrillators or pacemakers as monitors of atrial rhythm in a nested case‐control study. Twenty‐one LQTS patients (3 male; 39 ± 18 years old; 18 on β blocker, ICD therapy duration 6.3 ± 2.7 years; 4 LQT1, 6 LQT2, 2 LQT3) were matched to 21 control subjects (13 male; 50 ± 19 years old; 3 on β blocker; pacemaker therapy duration 8.5 ± 5.5 years; 19 higher‐degree AV block, 2 others). LQTS patients were identified by a systematic search of the LQTS patient databases in Münster and Munich.

Results: One‐third (7 of 21) of the LQTS patients developed self‐terminating atrial arrhythmias (atrial cycle lengths <250 ms). Only one control patient developed a single episode of postoperative AF (P < 0.05 vs LQTS).

Conclusions: LQTS patients at high risk for ventricular arrhythmias may develop short‐lasting atrial arrhythmias under daily‐life conditions, suggesting that prolonged atrial repolarization may contribute to the initiation of AF.