We read with great interest the recent study by Vlahou et al. on the role of mediastinal blood in triggering new-onset atrial fibrillation (AF) following cardiac surgery [1]. The authors conclude that postoperative AF (POAF) has a strong association with the volume of mediastinal drainage, based on their analysis of 1,140 patients who underwent cardiac surgery with cardiopulmonary bypass [1]. We would, however, like to present our observations on the research topic.

AF remains one of the most common and clinically significant postoperative arrhythmias following cardiac surgery [1–3]. The study by Vlahou et al. noted a POAF incidence of 33.59%, which falls within the overall reported incidence of POAF ranging from 10% to 63% after cardiac surgery [1, 2]. This wide range of incidence reflects the multifactorial etiology of this post-cardiac surgical complication, which in turn warrants a comprehensive evaluation of the baseline predisposition [1–3]. In this context, although initially developed for the assessment of the risk of stroke in AF, the CHA₂DS₂-VASc score has also been investigated as a predictor of POAF after cardiac surgery [3, 4]. Accordingly, several components of this score, such as congestive heart failure and vascular disease, appear not to have been unaccounted for in the analysis. Reporting these variables individually or as part of a composite CHA₂DS₂-VASc score may have provided additional insight into baseline susceptibility to POAF [1, 3, 4].

Among non-modifiable risk factors, patient age deserves particular attention. The risk of AF is reported to approximately double with each decade of life and exceed 20% by the age of 80 years [5]. For instance, the CHA₂DS₂-VASc score assigns +2 points for age ≥ 75 years, with +1 point being allotted to the patient age of 65–74 years [3, 4]. While age did emerge as an as an independent risk factor for POAF in the Vlahou et al. study in multivariable logistic analysis (odds ratio 1.03, 95% confidence interval 1.01–1.05, p = 0.001), it would have been informative to know whether the CHA₂DS₂-VASc score of those aged ≥ 75 years in the study would have exceeded that of patients aged below 75 years, given that the mean patient age was 66.1 ±10.1 years [1, 3, 4].

Moreover, the study included a diverse surgical subset undergoing coronary artery bypass grafting (CABG), isolated valve surgery, CABG with valve surgery, and ascending aorta replacement [1]. In addition to the potential heterogeneity contributed by the former, the concurrent POAF risk implications of baseline left atrial enlargement and left ventricular diastolic dysfunction should also not be overlooked [1, 6, 7]. Even for the dynamic factors, a systematic review and meta-analysis by Seo et al. involving 4,798 patients revealed postoperative inotrope use as a risk factor for POAF after CABG (p < 0.001) [8]. This is particularly relevant given that approximately half of the patients in the Vlahou et al. study underwent CABG and were monitored for the occurrence of new-onset AF throughout their postoperative hospital stay [1, 8].