Atrial fibrillation;Obstructive sleep apnea
With great interest we read the challenging paper by van Oosten et al.  who report on histological findings in right atrial musculature in patients undergoing coronary bypass grafting and their potential association with obstructive sleep apnea. As they summarize, there were no differences between patients at high or at low risk for OSAS, implicating that OSAS might not be associated with morphologic changes in the right atrium.
In this context, we would like to give some comments:
- As it is noted by the authors, they made a risk evaluation for the presence of OSAS using the Berlin questionnaire . Therefore there is a mismatch in diagnostic accuracy between high sophisticated histological analysis and a questionnaire which just deals with clinical risk evaluation. To tell the truth, authors could not really know, if the patients have sleep apneics, and if, they could not appreciate severity of breathing disorder. As it was shown by Gami et al.  the severity of sleep apnea is associated with incidence of atrial fibrillation. Consequently, one might assume that structural changes might be associated with severity of OSAS. This fact could not be addressed by the authors because of the study protocol.
- Atrial fibrillation is common in OSAS with an incidence of 14% in a mean follow-up of 4.7 years , contrary OSAS is much more frequently found in patients with atrial fibrillation, with a prevalence of about 50% . Until now, it is not possible to predict, which patient will develop atrial fibrillation and which will not. Severity of OSAS probably plays a role. One might consider hypoxia, oxidative stress, endothelial dysfunction, adrenergic stimulation due to apnea or intrathoracal pressure swings as important pathomechanism  leading to atrial remodeling with consecutive electrical instability. Since patients with atrial fibrillation were excluded from the study, one might speculate, why there should be morphologic alterations.
However, until today there is a multitude of reports dealing with interactions and associations between OSAS and the heart, mostly based on epidemiological or clinical studies. Therefore, we congratulate the authors on taking a step forward in this pathophysiologic interesting and clinically important field.
Conflict of interest
Authors declare no conflict of interests.
 E.M. van Oosten, A.H. Boag, K. Cunningham, J. Veinot, A. Hamilton, D. Petsikas, et al.; The histology of human right atrial tissue in patients with high-risk obstructive sleep apnea and underlying cardiovascular disease: a pilot study; IJC Heart Vasculature, 6 (2015), pp. 71–75
 N.C. Netzer, R.A. Stoohs, C.M. Netzer, K. Vlark, K.P. Strohl; Using the Berlin Questionnaire to identify patients at risk for the sleep apnea syndrome; Ann Intern Med, 131 (7) (1999), pp. 485–491
 A.S. Gami, D.O. Hodge, R.M. Herges, E.J. Olson, J. Nykodym, T. Kara, et al.; Obstructive sleep apnea, obesity, and the risk of incident atrial fibrillation; J Am Coll Cardiol, 49 (5) (2007), pp. 565–571
 M. Naughton, B. Sanner; Cardiovascular complications of sleep related breathing disorders; Prog Respir Res, 35 (2006), pp. 192–293