Can you feel the beat? How to define reference ranges for ambulatory heart rhythm monitoring

Since the ambulatory electrocardiogram (ECG) recording device was first put in clinical use in 1954, ECG monitoring has become an essential tool for the diagnosis of intermittent cardiac arrhythmias, both as relatively short recordings of 24–48 hours, and as longer ECG monitoring, which is now widely available using a variety of devices. In addition to clearly abnormal findings such as sustained atrial fibrillation (AF) or high-degree atrioventricular (AV) block, ambulatory ECG also provides information on a multitude of different findings. For example, supraventricular ectopy (SVE) is common1 and also associated with increased risk of AF, stroke and death,2 3 but we do not have any guidance on what defines a normal amount of SVE. Similarly, AF is commonly defined as 30 s of irregular arrhythmia without p-waves, but shorter supraventricular runs with AF characteristics are common and associated with an increased risk of AF.4 5 Thus, despite widespread clinical use, there is a surprising lack of research about ambulatory ECG monitoring and very little evidence about established reference ranges for common arrhythmias. The study presented in this issue of Heart therefore presents timely data on this important topic. Curtis et al performed a systematic review and meta-analysis of published studies reporting the frequency of common cardiac arrhythmias.6 The inclusion criteria were studies reporting original data on ≥24-hour ECG monitoring in at least 20 subjects aged 18 years or older. Studies that reported data on either endurance athletes or studies with a high prevalence of cardiovascular disease, diabetes or hypertension were excluded; this latter category also comprised some studies that reported on general population samples. Thirty-three studies with a total of 6466 study subjects were included, and weighted pooled estimates with 95% CIs for the prevalence of sinus pauses of ≥2 or ≥3 s, first-degree AV-block, …