Is Anticoagulation Necessary for Post-CABG Surgery Atrial Fibrillation?

By Michael H. Crawford, MD, Editor

SYNOPSIS: A meta-analysis of non-randomized trials of oral anticoagulant use for new atrial fibrillation (AF) after coronary artery bypass surgery involving almost 1.7 million patients has shown that AF is frequent, but the incidence of thromboembolism, bleeding, and death are low. Oral anticoagulants, when given, do not significantly affect thromboembolism or mortality rates, but they do increase bleeding.

SOURCE: van de Kar MRD, van Brakel TJ, Van’t Veer M, et al. Anticoagulation for post-operative atrial fibrillation after isolated coronary artery bypass grafting: A meta-analysis. Eur Hear J 2024;45:2620-2630.

The development of atrial fibrillation (AF) in hospital post-coronary artery bypass graft (CABG) surgery is common and usually temporary. Thus, there is controversy over whether oral anticoagulants (OACs) should be started and, if so, how long they should be continued. Since there are no randomized controlled trials to answer this question, these investigators from the Netherlands conducted a meta-analysis of studies of the use and non-use of OACs in new-onset AF post-CABG. The researchers identified 2,691 longitudinal studies from which 28 were selected for the meta-analysis. These 28 studies involved almost 1.7 million patients. The mean incidence of post-CABG AF was 24% (range, 8% to 38%). Of those who developed AF, 16% received an OAC, which usually was warfarin (63%). The 30-day post-operative incidence of a thromboembolic event (TE) was 1% (0.3% AF patients, 0.8% non-AF patients). The 30-day mortality rate was 2% (1% AF patients, 0.5% non-AF patients). Major bleeding occurred in 1.1% of AF patients and in 2.7% of non-AF patients. Over a 4.6-year median follow-up per 100 patient-years, TE occurred in 1.73 AF patients vs. 1.14 non-AF patients, mortality was 3.39 in AF and 2.19 in non-AF, and bleeding rates were 2.0 in AF and 1.6 in non-AF.

Four studies compared OAC use to no OAC use and found that TE rates (hazard ratio [HR], -0.11; 95% confidence interval [CI], -0.36-0.13) and mortality (HR, -0.07; 95% CI, -0.21-0.70) were not significantly different, but bleeding was higher with OACs (HR, 0.32; 95% CI, 0.06-0.58). The authors concluded that AF occurs in about one-quarter of post-operative CABG patients, but only one in six is given an OAC. The frequency of complications is low, but it is higher in AF vs. non-AF patients. OACs do not significantly reduce complications, but they do increase bleeding.

COMMENTARY

Perhaps the most surprising result of this study is the low rate of TE with post-CABG AF. When the investigators looked at the time frame over a year, TE was most common in-hospital (1.6%) and then progressively decreased: 1% at 30 days and 0.6% at one year. This suggests that post-CABG AF may have a unique pathophysiology related to the surgery. On the other hand, bleeding was more common in the 30-day time frame and may explain the variability in OAC use. Mortality was low in-hospital (1.4%) and at 30 days (2%), but rose at one year to almost 4%, with AF patients having the highest mortality (6.4% vs. 2.7%). Since OAC use did not affect the incidence of TE or mortality but increased bleeding, some studies concluded that OACs were deleterious in post-CABG AF. The most recent guidelines advise using OACs based on the patient’s long-term risk profile, but they do not specify how this is done.¹ Some believe the CHA₂DS₂-VASc score would be the appropriate instrument, but there was no consensus among the studies in this meta-analysis on this point.

There are several weaknesses to this study besides being a meta-analysis. There were few studies of OAC use. Warfarin was the most frequently used OAC, but three studies did compare it to the direct OACs and found no differences. Also, compliance with OACs was not assessed.

The role of risk factors for AF, such as hypertension, diabetes, and heart failure, was not explored. There was no consideration of the role of antiplatelet use. In addition, the application of left atrial appendage closure during CABG was not analyzed. However, this was a comprehensive meta-analysis involving a large number of patients with well-defined inclusion criteria. At this point, it is clear that a randomized controlled trial is needed to evaluate the efficacy and safety of OAC use in this population.

REFERENCE

1. Hindricks G, Potpara T, Dagres N, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS): The task force for the diagnosis and management of atrial fibrillation of the European Society of Cardiology (ESC) developed with the special contribution of the European Heart Rhythm Association (EHRA) of the ESC. Eur Heart J 2021;42:373-498.