The autonomic nervous system plays an important part in the initiation and perpetuation of atrial fibrillation.^1,2 Increased central sympathetic outflow and efferent cardiac sympathetic nerve stimulation can enhance the development of atrial fibrillation.

Background: The Heart Rhythm Society consensus statement arbitrarily defines atrial fibrillation (AF) ablation failure as any episode ≥30 seconds. However, if brief AF events are not correlated to longer events, the rationale for this end point is questionable. We determined the impact of AF episode duration threshold on AF incidence and burden. Methods: Patients with a pacemaker in a prospective registry with device-detected AF and follow-up >30 days were analyzed. AF patterns were calculated for various AF duration thresholds (30 s; 2 and 6 minutes; 3.8, 5.5, and 24 hours) selected based on published consensus statements, established evidence of stroke risk, and device capabilities. Freedom from AF postdevice implant at each AF episode duration threshold was assessed, as was overall AF burden. Results: Among 615 patients with pacemaker (aged 72.0±11.8 years, 54.2% male, follow-up 3.7±2.2 years) with device-detected AF, 599 had ≥1 AF episode of ≥30 seconds duration (median, 22 episodes). At 12 months, freedom from AF was 25.5%, 30.1%, 34.6%, 52.6%, 56.5%, and 73.1% for duration thresholds of 30 seconds, 2 minutes, 6 minutes, 3.8 hours, 5.5 hours, and 24 hours, respectively. Of patients with a first episode of 30 seconds to 2 minutes, 35.8% were free from subsequent episode >2 minutes at 180 days. Median AF burden was significantly less for patients with first episodes between 30 seconds and 3.8 hours versus >3.8 hours (0.2% versus 9.5%, respectively; P <0.0001). Conclusions: Small differences in AF episode duration definition can significantly affect the perceived incidence of AF and impact reported outcomes, including AF ablation success. An initial AF episode of 30 seconds does not predict clinically meaningful AF patterns.

Ambulatory ECG (AECG) is very commonly employed in a variety of clinical contexts to detect cardiac arrhythmias and/or arrhythmia patterns which are not readily obtained from the standard ECG. Accurate and timely characterization of arrhythmias is crucial to direct therapies that can have an important impact on diagnosis, prognosis or patient symptom status. The rhythm information derived from the large variety of AECG recording systems can often lead to appropriate and patient‐specific medical and interventional management. The details in this document provide background and framework from which to apply AECG techniques in clinical practice, as well as clinical research.