Episodes of atrial fibrillation (AF) lasting ≥5.5 hours detected in patients with cardiac implantable electronic devices (CIEDs) were associated with a more than 3-fold increase in odds of ischemic stroke, according to a large case-crossover study published recently in JAMA Cardiology.
According to the findings, the increase in risk was as high as 5-fold within the first 1-5 days after occurrence of the arrhythmia which, the authors point out, is consistent with traditional views that AF is “directly and transiently associated with ischemic stroke.”
"Overall, these findings significantly underscore traditional thinking that AF is likely a causal risk factor for ischemic stroke as opposed to just a risk marker," said Daniel Singer, MD, professor of medicine at Harvard Medical School, professor in the Department of Epidemiology at the Harvard T.H. Chan School of Public Health, and Division of General Internal Medicine at Massachusetts General Hospital, in a statement. "The results indicate that prolonged episodes of AF increase stroke risk, but this risk decreases rapidly following the end of the episode. These findings raise the possibility that time-limited anticoagulation for infrequent episodes of AF may be an effective stroke prevention strategy."
Singer and colleagues set out to learn more about the temporal association between episodes of AF and ischemic stroke that could improve understanding of the mechanism underlying the relationship as well as inform future treatment of paroxysmal AF.
The investigators tapped data for 466 635 individuals in a large national electronic health record database that was linked to a vendor database of patients with CIEDs. Of the total 466 635 individuals, Singer et al identified 891 who sustained an ischemic stroke and had 120 days of continuous heart rhythm recording prior to the ischemic event.
Median age of this group was 76 years; 64.5% were men; 52.1% had a prior stroke or transient ischemic attack; and 47.8% had a clinical diagnosis of AF.
Data were collected from January 2007 to March 2017 and analyzed from November 2019 to June 2020.
The exposure of interest for the study was defined as AF ≥5.5 hours during days 1-30 vs a control period that included days 91-120 prestroke.
The researchers found that three-quarters (76.5%, 682)) of subjects had no AF meeting the threshold in either 30-day period; 16% (143) had at least one day with AF ≥5.5 hours in both periods; and 7.4% (66) had informative, discordant rhythm patterns (ie, AF <5.5 hours in only on period).
* Among the 66 patients with informative, discordant arrhythmias, 52 had AF ≥5.5 hours in the case period vs 14 in the control period (odds ratio [OR], 3.71; 95% confidence interval [CI]CI, 2.06-6.70).
* Stroke risk was increased most in days 1 to 5 following an AF episode (OR, 5.00; 95% CI, 2.62-9.55).
* AF >23 hours on a given day was associated with the clearest increase in stroke risk (OR, 5.00; 95% CI, 2.08-12.01).
Singer et al note in their conclusion that the excess stroke risk above baseline observed in the study was highest within 5 days of an episode and then diminished rapidly, further supporting long-held views that AF has a direct and transient association with ischemic stroke. "These results provide support for trials of time-delimited anticoagulation for patients with infrequent multihour episodes of AF and rigorous, continuous rhythm monitoring," they wrote.
Reference: Singer DE, Diegler PD, Koehler JL, et al. Temporal assocation between episodes of atrial fibirllation and risk of ischemic stroke. JAMA Cardiol. Published online September 29, 2021. doi:10.1001/jamacardio.2021.3702.