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Editorials

Postoperative atrial fibrillation and stroke—is it time to act?

Pages 69-70 | Received 09 Jan 2014, Accepted 11 Jan 2014, Published online: 20 Feb 2014

Postoperative atrial fibrillation (AF) affects one-third of patients undergoing cardiac surgery, and is the most common complication after the procedure. The typical form is an episode of AF with an onset at the second postoperative day, lasting one or two days, and with the patient discharged in sinus rhythm (SR). Postoperative AF belongs to the family of secondary AF, also encountered after major trauma or surgery and sepsis. It is a robust complication, responding only moderately to heavy prophylactic treatment, and there are no reliable clinical models of prediction. Some studies have shown associations with an increased morbidity and risk of stroke in the immediate postoperative period, but otherwise it has been considered a benign episode of minimal or no consequences for the future.

It therefore came as a surprise when a follow- up of 6475 coronary artery bypass graft (CABG) patients showed that the patients with an episode of postoperative AF had an increased long-term mortality at 5 years (Citation1). This finding was confirmed in subsequent studies, and the risk of cardiovascular death in particular was found to be increased (Citation2,Citation3). The hazard ratios of long-term mortality in patients with an episode of AF compared to those of patients in SR at surgery were 1.5–2.1 in these studies, which should be compared to the hazard ratio of 1.5–1.9 in (nonsurgical) patients in AF compared to patients in SR in the Framingham study (Citation4). The basic question is, of course, whether postoperative AF is a marker of a more severe cardiovascular disease, or whether it is the tendency to develop AF in itself that constitutes the increased risk. In other words, which confounders are controlled for?

In the current issue of this journal, Thorén et al. use data from the Swedish Death Registry to explore the correlation between postoperative AF and cause-specific mortality, looking into both primary and underlying causes of death (Citation5). Their results show a significantly higher risk for cardiac death, or death related to arrhythmia, cerebrovascular disease and heart failure among patients experiencing postoperative AF at surgery compared to patients in SR, and that this effect was constant many years postoperatively. The confounders controlled for were age, hypertension, diabetes, number of prior myocardial infarctions, coronary artery anatomy and left ventricular ejection fraction.

In analyzing the results of Thorén et al. together with the results of previous studies, there are some caveats. One important factor not controlled for is left ventricular diastolic dysfunction, which is correlated to AF, advanced age, and late mortality, and is thus a potential confounder in all these studies. The rate of patients receiving anticoagulation at follow-up is also unknown. One possible explanation for the observed increased risk is that postoperative AF reveals a tendency to develop AF under stress, and so postoperative AF is an indicator for later development of AF. Indeed, in one study postoperative AF patients had an eightfold increased risk of future development of AF (Citation6), and studies have consistently shown an increased risk of cerebrovascular death among postoperative AF patients.

These findings may also cast some light on the results from the Syntax and Freedom trials.

These trials comparing percutaneous coronary intervention (PCI) and CABG show a consistent difference in stroke rate. In the Syntax trial, the stroke incidence at one-year follow-up was 2.2% in the CABG group compared to 0.6% in the PCI group (Citation7), while in the Freedom trial, the stroke incidence at 5 years was 5.2% in the CABG group and 2.4% in the PCI group (Citation8). It is worth noting that the incidence of postoperative AF was not recorded in these trials. Since postoperative AF after PCI is a very rare event as far as we know, the differences in stroke rate may partly be explained by episodes of (unprotected) postoperative AF among CABG patients. Together, all these findings raise the important question: how are CABG patients treated today with regard to antithrombotic and anticoagulation therapy, and is there need for a change in patients experiencing postoperative AF?

All patients undergoing CABG are offered single or dual antiplatelet therapy depending on the presence of drug-eluting stents and type of coronary artery disease (Citation9,Citation10). However, antiplatelet therapy offers only moderate protection against thromboembolic disease in patients with AF (Citation11). The indication for anticoagulation in patients with an episode of postoperative AF does not essentially differ from other types of AF. Given the short duration of a typical episode of postoperative AF, warfarin is seldom prescribed at discharge [3.6% of postoperative AF patients in one study (Citation6)].

The important message from the findings of Thorén et al. and previous researchers is that postoperative AF patients have a sustained long-term risk of cardiovascular death and especially thromboembolic cerebral complications. The risk of future development of AF, which may be asymptomatic, merits increased attention. We have reason to believe that some postoperative AF patients experience asymptomatic AF episodes at home, which are unprotected. Therefore, a randomized trial comparing, for example, one of the novel oral anticoagulants to placebo in patients with one episode of postoperative AF would be of great interest. Although the numbers of patients needed in such a study would be great, the consistently higher stroke rate in CABG patients needs to be addressed. Is a Scandinavian multicentre study a possible way of moving forward?

Declaration of interest: The author report no declarations of interest. The author alone is responsible for the content and writing of the paper.

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