Ectopic atrial rhythm
There are several sinus node ECG findings related to the “athlete’s heart”.
Moderate and asymptomatic sinus bradycardia (HR 40-50 bpm), or parasympathetic predominance, is the most common disorder in endurance athletes. Its prevalence is especially high in athletes of high-level aerobic resistance sports (cyclists, marathon runners, skiers). Severe bradycardia (HR < 35-40 bpm) is rare, although it can be present in older sports people (> 40 years old) and occurs more so at night-time. Irrespective of the baseline heart rate, sinus bradycardia is considered benign if the patient remains asymptomatic and a normal increase in heart rate (chronotropic response) is observed during exercise stress testing.
Sinus arrhythmia is frequent (up to 15-20% of athletes), and so are sinus pauses that last longer than 2 seconds (up to one third of patients) whether at night or during the day. When the baseline heart rate is low, it is possible to find a competing nodal rhythm (0.5-2.5% of patients or an ectopic atrial rhythm (13.5-69% of patients). Again, these findings are not worrying and the individual can be safely reassured if normal sinus rhythm appears during exercise.