Clinical relevance of arrhythmias during sleep: guidance for clinicians

ardiac rhythm during sleep is influenced by the autonomic nervous system and various pathologic states.Most arrhythmias that occur during sleep are detected incidentally on Holter recordings, and are in fact benign.Although such findings may not necessitate further investigation, they may be an important clue to an underlying disorder in need of investigation and treatment.It is important to recognise predisposing factors to sleep related arrhythmia in order to prevent and treat potentially dangerous cardiac rhythms.It is also important to establish a threshold for referral to a cardiologist or electrophysiologist once such arrhythmias are detected. NORMAL CARDIAC RHYTHM DURING SLEEP cSleep is a dynamic and complex process.The stages of sleep, conventionally divided into rapid eye movement (REM) and non-rapid eye movement (non-REM), are characterised by unique autonomic influences over cardiac rhythm and haemodynamics.Non-REM sleep is graded 1-4 according to electroencephalogram (EEG) characteristics and diminished arousability.REM sleep occurs at approximately 90 minute intervals, encompasses most dream activity, and is characterised by rapid eye movements and reduced voluntary muscle activity.Studies of individuals free of cardiac disease show that sinus bradycardia, sinus pauses, and type 1 second degree atrioventricular (AV) block are common during sleep (table 1). 1 Sinus pauses up to two seconds in duration occur commonly in young people in association with sinus arrhythmia (fig 1). 1 This is seen more frequently in athletes, w1 and less frequently in those over 80 years of age.w2 These arrhythmias are, for the most part, both asymptomatic and benign.They are a reflection of changes in autonomic tone that occur during sleep and require no intervention unless accompanied by symptoms. 2 AUTONOMIC INFLUENCE ON CARDIAC RHYTHM DURING SLEEPNon-REM sleep is characterised by an overall increase in parasympathetic tone, and a decrease in sympathetic tone (table 2).Parasympathetic tone is controlled by circadian rhythms, and sympathetic tone by sleep stage and the changes in posture and activity accompanying sleep.w3 In a study that compared results from individuals after a night of sleep and then a subsequent night deprived of sleep, sympathetic activity, as measured by the systolic pre-ejection period, differed significantly between the two nights.w4 There was no difference in parasympathetic activity which was measured by the degree of sinus arrhythmia.This implies that parasympathetic mediated arrhythmias may persist in the awake patient overnight.This may give rise to arrhythmias detected at night on Holter monitoring or inpatient cardiac monitoring even in the awake patient-a finding that does not necessarily imply the need for therapeutic intervention.Further monitoring may be appropriate to ensure that such arrhythmias are within normal limits, as described above.Night time reduction in sympathetic tone is reflected in the diminished incidence of premature ventricular contractions (PVCs) during sleep 2 w5 despite a relatively slow heart rate.Evidence in support of this demonstrates that suppression of PVCs by sleep predicts success of b blockade in PVC suppression.w6 Sleep suppression of PVCs is attenuated in patients with coronary artery disease or congestive heart failure, w5 likely due to increased baseline sympathetic tone.The natural suppression of hypercapnia induced ventilation during sleep and resulting hypoxia may also be a factor.Thus persistent, frequent PVCs may well be detected in patients with coronary artery disease when monitored (fig 2).Although such a finding may be unsettling, an abundance of evidence has shown that aggressive treatment of asymptomatic PVCs with antiarrhythmic medications is inappropriate in most situations.Non-sustained ventricular tachycardia (VT) may also be detected on monitoring, the management of which depends on assessment of symptoms, haemodynamic compromise, and ejection fraction.For patients with non-sustained VT in the presence of a poor ejection fraction, recent primary prevention trials have shown survival benefit with implantable cardioverter-defibrillators (ICDs). 3 4