Background: Congenital long QT syndrome (LQTS) is a familial arrhythmogenic cardiac channelopathy characterized by prolonged ventricular repolarization and increased risk of torsades de pointes-mediated syncope, seizures, and sudden cardiac death (SCD). QT prolongation corrected for heart rate (QTc) is an important diagnostic and prognostic feature in LQTS. Obstructive sleep apnea (OSA) has been increasingly implicated in the pathogenesis of cardiovascular disease, including arrhythmias and SCD. We tested the hypothesis that the presence of concomitant OSA in patients with LQTS is associated with increased QT intervals, both during sleep and while awake.
Methods and results: Polysomnography with simultaneous overnight 12-lead electrocardiography (ECG) was recorded in 54 patients with congenital LQTS and 67 control subjects. OSA was diagnosed as apnea-hypopnea index (AHI) ≥ 5 events/h for adults and AHI > 1 event/h for children. RR and QT intervals were measured from the 12-lead surface ECG. QTc was determined by the Bazett formula. Respiratory disturbance index, AHI, and arousal index were significantly increased in patients with LQTS and with OSA compared to those without OSA and control subjects. QTc during different sleep stages and while awake was also significantly increased in patients with LQTS and OSA compared to those without OSA. Severity of OSA in patients with LQTS was directly associated with the degree of QTc.
Conclusions: The presence and severity of obstructive sleep apnea (OSA) in patients with congenital long QT syndrome (LQTS) is associated with increased QT prolongation corrected for heart rate, which is an important biomarker of sudden cardiac death (SCD). Treatment of OSA in LQTS patients may reduce QT prolongation, thus reducing the risk of LQT-triggered SCD.
Keywords: hypoxia; long-QT syndrome; sleep apnea; torsade de pointes.
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