'Oral anticoagulation not effective in patients with atrial high-rate episodes'

AMSTERDAM: According to a study presented in a Hot Line session at ESC Congress 2023, blood thinners (anticoagulants) cause bleeding without preventing stroke in individuals with atrial high rate episodes (AHRE), but without electrocardiogram (ECG)-diagnosed atrial fibrillation.

The findings of the study were published in the New England Journal of Medicine.

Anticoagulants work to prevent strokes in people with atrial fibrillation, but they are ineffective in people without it, such as people with heart failure. Atrial high-rate episodes (AHRE) are brief and uncommon atrial arrhythmias that resemble atrial fibrillation and are picked up by pacemakers, defibrillators, and loop recorders that are implanted in the body. 10% to 30% of individuals with implanted devices have AHRE.2 Even while people with AHRE have a higher risk of stroke, this risk is still lower than that of people with atrial fibrillation. In individuals with atrial fibrillation and elevated stroke risk, ESC recommendations advise oral anticoagulation to avoid stroke, and they advocate personalised decisions in patients with AHRE but no ECG evidence of atrial fibrillation.

NOAH-AFNET 6 was the first trial to investigate the efficacy and safety of oral anticoagulation in patients with AHRE, but without ECG-documented atrial fibrillation. The randomised, double-blind, double-dummy trial compared the anticoagulant edoxaban to placebo in patients ≥65 years with AHRE episodes ≥6 minutes detected by implantable devices, and with at least one additional stroke risk factor (heart failure, hypertension, diabetes, prior stroke or transient ischaemic attack, vascular disease, or age ≥75 years). This patient population was outside the approved indication of edoxaban.

In 206 sites across 18 European countries, patients were randomly allocated in a 1:1 fashion to anticoagulation or no anticoagulation. Anticoagulation consisted of edoxaban in the dose approved for stroke prevention in atrial fibrillation (60 mg once daily, reduced to 30 mg once daily according to approved dose reduction criteria for stroke prevention in atrial fibrillation). No anticoagulation consisted of placebo containing no active compound or aspirin 100 mg once daily in patients with an indication for antiplatelet therapy. The primary outcome was a composite of stroke, systemic embolism, or cardiovascular death. The safety outcome was a composite of major bleeding and all-cause death. All patients were followed until the end of the trial.

The primary, modified intention-to-treat analysis population consisted of 2,536 patients who received at least one dose of study drug. Patients were elderly with multiple stroke risk factors: the mean age was 78 years, 37% were women and the median CHA2DS2-VASc score was 4.5 The median AHRE duration at baseline was 2.8 hours without an upper limit, and 97% of AHRE showed atrial rates >200 beats per minute, clearly resembling atrial fibrillation.

The trial was stopped early due to safety signals and a trend towards futility for efficacy after enrolment of all planned patients. The primary efficacy outcome occurred in 83 patients in the anticoagulation group (3.2%/year) and in 101 patients in the no anticoagulation group (4.0%/year), for a hazard ratio (HR) of 0.81 (95% confidence interval [CI] 0.6-1.1]; p=0.15). The stroke rate was low in both randomised groups (without anticoagulation 1.1%/year, with anticoagulation 0.9%/year). The primary safety outcome occurred in 149 patients in the anticoagulation group (5.9%/year) and in 114 patients in the no anticoagulation group (4.5%/year), for a HR of 1.3 (95% CI 1.0-1.7; p=0.03). The difference in safety outcomes was driven by an expected increase in major bleeding in patients receiving anticoagulation (HR 2.10; 95% CI 1.30-3.38; p=0.002). ECG-diagnosed atrial fibrillation developed in 462/2536 patients (18%; 8.7%/year).

Principal investigator Paulus Kirchhof of the University Heart & Vascular Center Hamburg, Germany said: “The NOAH-AFNET 6 trial found that oral anticoagulation in patients with AHRE increases bleeding without reducing a composite outcome of stroke, systemic embolism, or cardiovascular death. The increased bleeding on anticoagulation therapy was expected. The low stroke rate with and without anticoagulation was unexpected. The results of NOAH-AFNET 6 clearly suggest to demand ECG documentation of atrial fibrillation prior to initiation of oral anticoagulation. Further research is needed to better understand the stroke risk in patients with very rare and short atrial arrhythmias.”