The online-only Data Supplement is available at http://circep.ahajournals.org/lookup/suppl/doi:10.1161/CIRCEP.113.000266/-/DC1. Correspondence to Ken-ichi Maeno, MD, Sleep Center, Toranomon Hospital, 2-2-2 Toranomon, Minato-ku, Tokyo 105-8470, Japan, E-mail maeken@zk9.so-net.ne.jp Background-Prolonged P-wave duration, indicating atrial conduction delay, is a potent precursor of atrial fibrillation.Obstructive sleep apnea (OSA) is a risk factor for atrial fibrillation development. We investigated the association of P-wave duration with OSA and its treatment. Methods and Results-We enrolled 80 consecutive men with normal sinus rhythms who underwent polysomnography, had no history of atrial fibrillation or ischemic heart disease, and no evidence of heart failure. Signal-averaged P-wave duration (SAPWD) was measured in all participants. Multivariable regression analysis showed that age, hypertension, and log-transformed apnea-hypopnea index were significantly and independently correlated with SAPWD. SAPWD was repeatedly measured after 1 month of continuous positive airway pressure (CPAP) therapy in 62 patients with moderateto-severe OSA. As controls, 18 patients with moderate-to-severe OSA were enrolled. Their SAPWD was also measured at baseline and after 1 month without CPAP therapy. No significant change in SAPWD was found between baseline and after 1 month in the controls. However, SAPWD was significantly shortened after 1 month of CPAP therapy (from 137.5±8.6 to 129.7±8.5 ms; P<0.001), and the SAPWD change was significantly different in patients with CPAP therapy compared with controls (P<0.001). In addition, the SAPWD change in patients with CPAP therapy correlated inversely with nightly CPAP usage (r=−0.52; P<0.001). Conclusions-OSA severity was significantly associated with prolonged SAPWD. CPAP therapy significantly shortened SAPWD in patients with moderate-to-severe OSA. Thus, OSA may cause atrial conduction disturbances, leading to an increased risk of atrial fibrillation development, which may be modifiable by alleviating OSA with CPAP therapy. (Circ Arrhythm Electrophysiol. 2013;6:287-293.)

No abstract