Clinical relevance of arrhythmias during sleep: guidance for clinicians

REM sleep occurs approximately 4-6 times per night for 90 minute periods, characterised by surges of sympathetic activity and decreased baroreceptor regulation and control. 10 The highest incidence of non-fatal myocardial infarction, implanted defibrillator discharges, and sudden cardiac death occurs in a non-uniform manner throughout the night. 10 A surge in each of these events occurs between 5 and 6 am, coinciding with an increased incidence of REM sleep. Several mechanisms are likely involved in this phenomenon, including diminished myocardial perfusion and increased electrical instability caused by high sympathetic tone, as well as a diminished ventilatory response to hypercapnia resulting in relative hypoxia and acidosis.\n Clinical relevance of arrhythmias during sleep: key points Although most arrhythmias detected during sleep are benign, they may indicate an underlying disorder in need of investigation and treatment Sinus bradycardia, sinus pauses up to two seconds in duration, and type 1 second degree atrioventricular block are commonly observed during sleep, and are generally benign Nocturnal arrhythmias associated with structural heart disease or associated symptoms warrant investigation and consideration for specialist referral Rates of sudden cardiac death, ventricular arrhythmias, and shocks delivered by implantable cardioverter-defibrillators are highest upon awakening in the morning hours, likely related to changes in autonomic tone Obstructive sleep apnoea, a condition which may predispose to serious cardiovascular sequelae, can cause cyclic variation of the heart rate during sleep.