REM sleep and bradyarrhythmia episodes in rats

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.

REM sleep-related brady-arrhythmia syndrome

Rapid eye movement (REM) sleep-related brady-arrhythmia syndrome is a cardiac rhythm disorder characterised by asystoles lasting several seconds during REM sleep in otherwise healthy individuals. In contrast to arrhythmias associated with obstructive sleep apnea, REM sleep-related sinus arrests and atrioventricular (AV) blocks are not associated with episodes of apnea or hypopnea. In literature, only few cases have been published, suggesting that the prevalence of this nighttime rhythm disorder is very rare. In this paper, we report two new cases of REM sleep-related sinus arrests and one case of REM sleep-related total AV block. To explore the underlying mechanism, an analysis of heart rate variability was performed. In a matched control population, we observed a significant lower low-to-high frequency (LF/HF) ratio in slow wave sleep as compared to REM sleep (2.04 +/- 1.2 vs 4.55 +/- 1.82, respectively [Mann-Whitney U test p < 0.01]), demonstrating a global increase in sympathetic activity during REM. When using the same technique in two of three patients with REM-related arrhythmias, the shift to an increased LF/HF ratio from slow wave sleep to REM sleep tended to be lower. This may reflect an increased vagal activity (HF component) during REM sleep in these subjects. We, therefore, hypothesise that, in our patients with REM sleep-related arrhythmias, the overall dominance of sympathetic activity during REM is present but to a lesser extent and temporarily switches into vagal dominance when the bursts of REMs occur. As it was still unclear whether these REM sleep-related asystoles needed to be paced, we compared our treatment and these of previously reported cases with the current American College of Cardiology/American Heart Association guidelines for implantation of cardiac pacemakers.

Cardiac arrhythmias during normal sleep and in obstructive sleep apnea syndrome

Normal sleep is associated with a slowing in heart rate due to a relative shift from sympathetic to parasympathetic neural dominance. Bradyarrhythmias consisting of sinus bradycardia, sinus arrest and second degree (Mobitz type 1) heart block are not uncommon in young adults. With aging, bradyarrhythmias decrease in frequency while atrial arrhythmias and ventricular ectopy increases. Patients with obstructive sleep apnea (OSA) have been demonstrated to have bradyarrhythmias and increased ventricular ectopy in association with apneas when oxyhemoglobin desaturations become severe. Although retrospective studies have suggested that cardiovascular mortality may be increased in patients with OSA, this remains to be proven in prospective clinical studies. Sudden death during sleep secondary to apnea related brady or ventricular tachyarrhythmias may occur. However, this is likely to be a very rare event that remains to be documented in the literature.

Is sudden unexplained nocturnal death a breathing disorder?

Sudden unexplained nocturnal death syndrome (SUNDS), or 'Lai Tai' in northeastern Thai dialects usually occurs during sleep in healthy young adults, mostly male. The characteristics of Lai Tai are similar to SUNDS which has been reported in several southeast Asian countries and in Japan by the name of 'Bangungut' in Tagalog or 'Pokkuri' in Japanese. The condition has been recognized by the people in the northeastern part of Thailand for many years. Elderly people in the region have described 'Lai Tai' victims as making loud groans and showing signs of difficulty in breathing or labored respiration, who become rigid and die. Data, from relatives or those who had witnessed the episodes of deaths, revealed that the deaths usually occurred in the same manner as described by the elderly. The data also reported that the patients were unresponsive and difficult to arouse. From these reports it is likely that the instability of the physiological systems, especially respiration, in particular during the REM phase, may play some roles in precipitating the sudden death.