Fainting in your sleep?

Sleep syncope-A systematic review

Background

Sleep syncope is a subtype of vasovagal syncope in which patients experience syncope after awakening from their sleep. The aim was to investigate the association of clinical characteristics and gastrointestinal symptoms with syncope, as well as the body position in which symptoms began.

Methods

A systematic search of studies was performed in MEDLINE and EMBASE without language restrictions, from inception to 9 January 2022. Studies were included if they reported data on the proportion of patients who experienced symptoms (nausea, vomiting, abdominal pain, and diarrhea) associated with syncope.

Results

Data were included for 116 patients in 13 studies. Patients were 46.9 ± 4.3 years and 61.4% were female. In 52.5% of patients, a supine body position at the time of syncope was reported. A history of phobias was reported by 67.6% of patients, and 96.5% of patients also had typical daytime vasovagal syncope. In the 5 studies reporting the results of head-up tilt testing (n = 77), 90.9% of patients had positive tests. Gastrointestinal symptoms were present in the majority of patients with reported rates of 65.6% for upper gastrointestinal symptoms and 86.0% for lower gastrointestinal symptoms.

Conclusion

Patients with sleep syncope patients are predominantly female with a history of daytime vasovagal syncope. Gastrointestinal symptoms are present in the majority of patients and is therefore an important feature of sleep syncope.

Sleep syncope: a prospective cohort study

PURPOSE

Sleep syncope is defined as a form of vasovagal syncope which interrupts sleep. Long term follow-up has not been reported.

METHODS

Between 1999 and 2013 we diagnosed vasovagal syncope in 1105 patients of whom 69 also had sleep syncope. We compared these 69 patients in the sleep syncope group to 118 patients with classical vasovagal syncope consecutively investigated between 1999 and 2003. We compared baseline demography, syncope history, tilt test results and follow-up findings.

RESULTS

At baseline, age and gender distribution (mean ± standard deviation) of the classical VVS and sleep synocope groups were similar: 46 ± 21 vs. 47 ± 15 years (p  = 0.53), and 55% versus 66% female (p  = 0.28), respectively. Abdominal discomfort and vagotonia were more frequent in sleep syncope patients: 80% versus 8% and 33% versus 2% (p  < 0.001). Childhood syncope and blood-needle phobia were also more frequent in sleep syncope patients: 58% versus 15% and 69% versus 19% (p  < 0.001). Positive tilt test results were similar for the two groups (93% [classical VVS] vs. 91%; p  = 0.56). Blood pressure, heart rate and stroke volume changed in a similar manner from baseline to syncope (p  = 0.32, 0.34 and 0.18, respectively). Mean duration of follow-up for the classical VVS and sleep syncope groups, as recorded in the electronic records, were 17 (3-21) and 15 (7-27) years, respectively. Rates of mortality and of permanent pacemaker insertion were similar in the two groups: 16.2% (classical VVS) versus 7.6% (p  = 0.09) and 3% (classical VVS) versus 3% (p  = 0.9). Incidence of sleep episodes decreased from 1.9 ± 3 to 0.1 ± 0.3 episodes per year (p  < 0.001).

CONCLUSION

Sleep syncope is a subtype of vasovagal syncope with characteristic symptoms. Despite the severity of the sleep episodes, the prognosis is very good. Very few patients require permanent pacing, and nearly all respond to education and reassurance.

Syncope: Case Studies

Syncope, or the sudden loss of consciousness, is a common presenting symptom for evaluation by neurologists. It is not a unique diagnosis but rather a common manifestation of disorders with diverse mechanisms. Loss of consciousness is typically preceded by a prodrome of symptoms and sometimes there is a clear trigger. This article discusses several cases that illustrate the various causes of syncope. Reflex syncope is the most common type and includes neurally mediated, vasovagal, situational, carotid sinus hypersensitivity, and atypical forms. Acute and chronic autonomic neuropathies and neurodegenerative disorders can also present with syncope.

Initial Clinical Evaluation

The initial evaluation of patients with transient loss of consciousness (LOC) comprises a detailed medical history, physical examination, and 12-lead electrocardiogram. Because there are many causes of syncopal and nonsyncopal LOC, an adequate method of taking the clinical history, which is the cornerstone of diagnosing patients with transient LOC, should be used.

The different clinical presentations of vasovagal syncope

For some decades, after the introduction of the head-up tilt test into clinical practice, the clinical presentation of vasovagal syncope (VVS) has been classified as typical (or classical) and atypical (or non-classical). Some clinical features and recent data suggest that even unexplained falls and syncope during sleeping hours may be possible clinical presentations of VVS. In recent studies, tilt testing and carotid sinus massage by means of the 'method of symptoms' were performed in one group of patients with unexplained falls and in another group with unexplained syncope (presence of prodromal symptoms). Overall, tilt testing and carotid sinus massage displayed a high positivity rate in the group of patients with unexplained falls (about 60%), which was similar to that of the unexplained syncope group. These new data seem to indicate that some unexplained falls could be cases of atypical VVS/carotid sinus syncope with retrograde amnesia. Some clinical features suggest that syncope during sleeping hours is a form of VVS with a different clinical presentation: high prevalence of autonomic prodromes, of diurnal episodes of typical VVS and specific phobias, and of positive tilt testing with severe cardioinhibition.

Endogenous circadian rhythm in vasovagal response to head-up tilt

BACKGROUND

The incidence of syncope exhibits a daily pattern with more occurrences in the morning, possibly as a result of influences from the endogenous circadian system and/or the daily pattern of behavioral/emotional stimuli. This study tested the hypothesis that the circadian system modulates cardiovascular responses to postural stress, leading to increased susceptibility to syncope at specific times of day.

METHODS AND RESULTS

Twelve subjects underwent a 13-day in-laboratory protocol in which subjects' sleep-wake cycles were adjusted to 20 hours for 12 cycles. A 15-minute tilt-table test (60° head-up) was performed ≈4.5 hours after scheduled awakening in each cycle so that 12 tests in each subject were distributed evenly across the circadian cycle. Of 144 tests, signs/symptoms of presyncope were observed in 21 tests in 6 subjects. These presyncope events displayed a clear circadian rhythm (P=0.028) with almost all cases (17/21) occurring in the half of the circadian cycle corresponding to the biological night (10:30 pm to 10:30 am). Significant circadian rhythms were also observed in hemodynamic and autonomic function markers (blood pressure, heart rate, epinephrine, norepinephrine, and indices of cardiac vagal tone) that may underlie the circadian rhythm of presyncope susceptibility.

CONCLUSIONS

The circadian system affects cardiovascular responses to postural stress, resulting in greater susceptibility to presyncope during the night. This finding suggests that night-shift workers and people with disrupted sleep at night may have greater risk of syncope as a result of their exposure to postural stress during the biological night.

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.

Sympatho-vagal responses in patients with sleep and typical vasovagal syncope

Sleep syncope is a recently described form of vasovagal syncope that interrupts sleep. The pathophysiology of this condition is uncertain but a ‘central’ non-baroreflex-mediated trigger has been suggested. In the present study, we tested the hypothesis that patients with sleep syncope have abnormal sympatho-vagal responses to non-baroreflex, but normal responses to baroreflex stimuli. We collected historical data from SS patients (patients with vasovagal syncope with sleep syncope; n=16) and NSS patients (patients with vasovagal syncope without sleep syncope; n=35), including demography, and triggers and symptoms during syncope. MBP (mean blood pressure), HR (heart rate) and MSNA (muscle sympathetic nerve activity) in SS patients were compared with NSS patients and matched controls (n=16) during HG (handgrip), CPTs (cold pressor tests), HUT (head-up tilting) and tilt-induced pre-syncope. Patients and controls were of similar age and gender distribution [SS patients, age 46.0±4 years (69% female); NSS patients, 47.3±4 years (63% female); controls, 43.7±5 years (69% female)]. Compared with NSS patients, SS patients reported more fainting episodes: (i) triggered by phobias (75 compared with 37%; P=0.001); (ii) while in the horizontal position (44 compared with 6%; P=0.001); and (iii) associated with abdominal symptoms (69 compared with 9%; P=0.001). Compared with controls, the MBP response to HG was attenuated in SS patients (P=0.016), and MSNA (burst frequency and incidence) responses to CPT were attenuated in both syncope groups (SS, P=0.011 and 0.003 respectively; NSS, P=0.021 and 0.049 respectively). MSNA responses to HUT did not differ. For both non-baroreflex and baroreflex responses, there were no differences in any of the MSNA indices between the syncope groups. Patients with vasovagal syncope, with or without sleep syncope, have very similar sympatho-vagal responses to both non-baroreflex and baroreflex stimuli. This is consistent with sleep syncope being a subform of vasovagal syncope. Attenuation of sympathetic responses to non-baroreflex pathways may be important in the mechanism of vasovagal syncope.