Sleep and night-type arrhythmias

REM-related bradyarrhythmia syndrome

Cardiac arrhythmias during sleep are relatively common and include a diverse etiology, from benign sinus bradycardia to potentially fatal ventricular arrhythmias. Predisposing factors include obstructive sleep apnea and cardiac disease. Rapid eye movement (REM)-related bradyarrhythmia syndrome (including sinus arrest and complete atrioventricular block with ventricular asystole) in the absence of an underlying cardiac or physiologic sleep disorder was first described in the early 1980s. Although uncertain, the underlying pathophysiology likely reflects abnormal autonomic neural-cardiac inputs during REM sleep. The autonomic nervous system (ANS) is a known key modulator of heart rate fluctuations and rhythm during sleep and nocturnal heart rate reflects a balance between the sympathetic-parasympathetic systems. Whether the primary trigger for REM-related bradyarrhythmias reflects abnormal centrally mediated control of the ANS during REM sleep or anomalous baroreflex parasympathetic influences is unknown. This review focuses on the salient features of the REM-related bradyarrhythmia syndrome and explores potential mechanisms with a particular assessment of the relationship between the ANS and nocturnal heart rate fluctuations.

Experimental study on the relationship between cardiac arrhythmias and sleep states by ambulatory ECG-EEC monitoring

The relationship between cardiac arrhythmias and sleep states was investigated in rats using the ambulatory ECG-EEG monitoring system under the 14/10 light-dark illumination schedule. Records of 14 rats obtained over 94 days were analyzed. Bradyarrhythmias (SA block and AV block) and ventricular arrhythmias [ventricular premature contraction (VPC) and short run of VPCs (ventricular tachycardia, VT)] were observed. Average number of episodes of bradyarrhythmia per day was 7.5, and the ratio of SA block to AV block was 34.9% to 65.1%. Average VPC or VT occurrence per day was 0.9 or 0.1 times, respectively. Sleep states were divided into alertness, slow-wave sleep, and paradoxical sleep, and the relationship between sleep states and arrhythmias was investigated. Bradyarrhythmias appeared predominantly during paradoxical sleep, while ventricular arrhythmias appeared during alertness as well as paradoxical sleep. Bradyarrhythmic episodes decreased by right or left vagotomy 78% or 70%, respectively. Sinus bradyarrhythmias disappeared almost completely by the right vagotomy, while the occurrence of AV block decreased by the right or left vagotomy. Circadian rhythms in arrhythmias were also analyzed by the cosine-fitting technique, and significant circadian rhythms were demonstrated in both bradyarrhythmias and ventricular arrhythmias. Acrophases were 9:56 A.M. and 1:47 A.M., respectively. Occurrence of VT was rare, but the most frequent incidental time zone was immediately following transition from light effects (rest) to dark (activity). This knowledge of circadian rhythm effects in arrhythmias must be incorporated into improved treatment of arrhythmias.