The main aim of the current study was to investigate the associations of regular alcohol intake with incident stroke or systemic embolism in patients with established atrial fibrillation (AF), most of whom (84%) were on anti-coagulant therapy. The authors used combined data from two prospective studies of subjects with AF, followed for an average of 3 years. While they excluded subjects with “only short, potentially reversible AF episodes (e.g., as after cardiac surgery or sepsis)” about one half of subjects in the study were diagnosed as having paroxysmal AF. Reported alcohol at baseline and at subsequent examinations was classified as none, > 0 to < 1 drink/day, 1 to < 2 drinks/day, and ≥ 2 drinks/day.
The primary outcome was a composite of stroke and systemic embolism. Secondary outcomes were all-cause mortality, myocardial infarction, hospital admission for acute heart failure, and a composite of major and clinically relevant nonmajor bleeding. In their analyses, they adjusted for age, sex, education, hypertension, history of heart failure, history of diabetes, BMI, smoking status, physical activity, history of stroke, history of coronary heart disease, oral anticoagulation, history of renal failure, AF type, and health perception. With annual assessments, the investigators updated all covariates over time, if appropriate.
The main results indicated no significant effect of alcohol consumption on the risk of the major outcomes (stroke or systemic embolism). However, there were significant decreases in risk for several secondary outcomes. For hospital admissions for heart failure, in comparison with non-drinkers the HR for moderate drinkers was 0.60 (CI 0.41-0.87); further, among moderate drinkers the HR for myocardial infarction was 0.39 (CI 0.20 – 0.78), and for all-cause mortality the HR was 0.49 (CI 0.35-0.69).
Forum members had two major concerns with the paper. First, the authors failed to report specifically how alcohol consumption was associated with increased or decreased presence of AF during follow up, even though approximately one-half of subjects had only paroxysmal AF at baseline. Determining if alcohol consumption affected subsequent AF would be information of importance to practitioners who are advising their patients with AF regarding alcohol consumption.
Secondly, it was pointed out by Forum members that the results may have been affected by what is known as collider bias: as moderate drinking shows an inverse association with coronary heart disease (which is strongly related to the presence of AF), subjects who consumed alcohol prior to the baseline diagnosis of AF were probably different from those who had no prior alcohol exposure, and the results of combining these two groups (as was done in these analyses) may have been biased. Such bias usually tends to result in estimates of effect going toward the null.
While the reported results of no real effect of alcohol consumption on the risk of stroke or systemic embolism among patients with AF is encouraging, to decrease the risk of bias in future studies it will be important that such research attempts to separate subjects according to their prior use of alcohol before baseline measurements are assessed. The marked reduction in the risk of other major cardiovascular outcomes and total mortality, found in this study to be associated with light to moderate drinking, matches the results seen in most previous studies.
Reference: Reddiess P, Aeschbacher S, Meyre P, Coslovsky M, Kühne M, Rodondi N, et al, for the BEAT-AF and Swiss-AF investigators. Alcohol consumption and risk of cardiovascular outcomes and bleeding in patients with established atrial fibrillation. CMAJ 2020;193:E117-E123. doi: 10.1503/cmaj.200778