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Atrial fibrillation (AF) is the most common sustained rhythm disorder, affecting 1.53% of the Korean population with economic burden.1) The prevalence of AF is increased with age, ranging from 0.03% among individuals aged 20−29 years to 4.16% among those ≥80 years.2) Various implanted devices and wearable monitors allow early detection of cardiac arrhythmias including subclinical AF.3) Cardiac implantable electronic devices (CIEDs) with an atrial lead can monitor atrial rhythm and store the tracings. The atrial leads can sense activity in the atrium and detect pre-programmed events, such as atrial high rate episode (AHRE). European guideline used the rate criterion for AHRE ≥ 175 bpm and regarded AHRE as a subclinical AF.4) The incidence of AHRE in patients with CIED is 30−70%.4) Whereas very short episodes are clinically irrelevant, as they are not associated with an increased risk of stroke or systemic embolism,5) longer episodes (minimum 5−6 minutes) are associated with an increased risk of clinical AF and ischemic stroke.6)7)8) Thus, the criterion for AHRE duration is usually set as ≥ 5–6 minutes to reduce oversensing artefacts.9) While much effort has been devoted to determine whether AHREs are associated with stroke and systemic embolism, predictors for AHREs were not well established.
In this issue of Korean Circulation Journal, the clinical observations on AHREs in patients with pacemaker were reported by Kim et al.10) in a prospective, multicenter, observational study. The study was designed to investigate the predictors of AHRE and evaluate the clinical development of AF and cardiovascular events. A total of 816 patients, eligible for permanent pacemaker implantation based on the 2016 revised Korean indication guideline, were enrolled. Median follow up was 18 months. The device-programmed rate criterion for AHRE was ≥220 bpm. The AHREs were identified in 370 patients and those >6 minutes were in 112 patients (13.7%) during the entire study period, which are lower than the previous studies.6) The higher rate criterion for AHRE (220 bpm) could explain the differences. Most AHREs were observed within 6 months after pacemaker implantation. Clinical AF developed in 21.4% (24/112). Multivariate analysis demonstrated that the predictors for AHRE with a longest duration >6 minutes were LA diameter >41 mm (OR, 2.08; 95% CI, 1.25−3.45; p=0.005) and prior sick sinus syndrome (OR, 3.22; 95% CI, 1.91−5.43; p=0.050). Authors added sensitivity analysis of atrial pacing ratio replacing the diagnosis of sick sinus syndrome and showed consistent findings. AHREs were not associated with increased cardiovascular events. However, the study population and clinical outcomes were too small to show statistical significance. The study population was limited to those with pacemakers and normal left ventricular systolic function. It might have more clinical event, if patients with defibrillator and decreased ejection fraction were included.
Whereas clinical trials reported that AHREs lasting ≥5−6 minutes were associated with increased risk of clinical AF,7)8) stroke risk in AHRE patients was lower than in patient with clinical AF.6)7) Most clinical trials informing management of AF patients confined to clinical AF, in which ECG documentation of AF was a mandatory inclusion criterion. Although European guideline recommends considering oral anticoagulants for patients having AHRE >24 hours and high-risk scores for stroke,4) whether AHRE needs the same therapeutic requirements as clinical AF is presently unclear. Several randomized controlled trials are ongoing regarding this issue [Apixaban for the Reduction of Thrombo-Embolism in Patients with Device-Detected Subclinical Atrial Fibrillation (NCT 01938248) and Non-vitamin K Antagonist Oral Anticoagulants in Patients With Atrial High Rate Episodes (NCT 02618577)]
The present study reported by Kim et al.10) in this issue of Korean Circulation Journal impose an incremental step for managing AHRE detected in CIED. Further evidence is needed for the optimal management and benefit of oral anticoagulant for patients with AHRE. In the meantime, while awaiting the results of ongoing clinical trials, patient with multiple predictors should be thoroughly investigated for future development of AHRE and clinical AF.
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