Cardioinhibitory carotid sinus hypersensitivity predicts an asystolic mechanism of spontaneous neurally mediated syncope

Syncope in the Emergency Department: A Practical Approach

Syncope is a common condition encountered in the emergency department (ED), accounting for about 0.6-3% of all ED visits. Despite its high frequency, a widely accepted management strategy for patients with syncope in the ED is still missing. Since syncope can be the presenting condition of many diseases, both severe and benign, most research efforts have focused on strategies to obtain a definitive etiologic diagnosis. Nevertheless, in everyday clinical practice, a definitive diagnosis is rarely reached after the first evaluation. It is thus troublesome to aid clinicians' reasoning by simply focusing on differential diagnoses. With the current review, we would like to propose a management strategy that guides clinicians both in the identification of conditions that warrant immediate treatment and in the management of patients for whom a diagnosis is not immediately reached, differentiating those that can be safely discharged from those that should be admitted to the hospital or monitored before a final decision. We propose the mnemonic acronym RED-SOS: Recognize syncope; Exclude life-threatening conditions; Diagnose; Stratify the risk of adverse events; Observe; decide on the Setting of care. Based on this acronym, in the different sections of the review, we discuss all the elements that clinicians should consider when assessing patients with syncope.

Recent Advances and Future Directions in Syncope Management: A Comprehensive Narrative Review

Syncope is a highly prevalent clinical condition characterized by a rapid, complete, and brief loss of consciousness, followed by full recovery caused by cerebral hypoperfusion. This symptom carries significance, as its potential underlying causes may involve the heart, blood pressure, or brain, leading to a spectrum of consequences, from sudden death to compromised quality of life. Various factors contribute to syncope, and adhering to a precise diagnostic pathway can enhance diagnostic accuracy and treatment effectiveness. A standardized initial assessment, risk stratification, and appropriate test identification facilitate determining the underlying cause in the majority of cases. New technologies, including artificial intelligence and smart devices, may have the potential to reshape syncope management into a proactive, personalized, and data-centric model, ultimately enhancing patient outcomes and quality of life. This review addresses key aspects of syncope management, including pathogenesis, current diagnostic testing options, treatments, and considerations in the geriatric population.

Arrhythmic syncope: From diagnosis to management

Syncope is a concerning symptom that affects a large proportion of patients. It can be related to a heterogeneous group of pathologies ranging from trivial causes to diseases with a high risk of sudden death. However, benign causes are the most frequent, and identifying high-risk patients with potentially severe etiologies is crucial to establish an accurate diagnosis, initiate effective therapy, and alter the prognosis. The term cardiac syncope refers to those episodes where the cause of the cerebral hypoperfusion is directly related to a cardiac disorder, while arrhythmic syncope is cardiac syncope specifically due to rhythm disorders. Indeed, arrhythmias are the most common cause of cardiac syncope. Both bradyarrhythmia and tachyarrhythmia can cause a sudden decrease in cardiac output and produce syncope. In this review, we summarized the main guidelines in the management of patients with syncope of presumed arrhythmic origin. Therefore, we presented a thorough approach to syncope work-up through different tests depending on the clinical characteristics of the patients, risk stratification, and the management of syncope in different scenarios such as structural heart disease and channelopathies.

A case of vasovagal syncope associated with carotid sinus hypersensitivity: Effectiveness of tilt training and subsequent squatting

A 43-year-old man fainted on a train and was transported to our hospital by an ambulance. No structural heart diseases or neurological abnormalities were observed. Electrocardiogram on admission demonstrated a junctional escape rhythm with bradycardia at 39 bpm. Sick sinus syndrome was excluded from electrophysiological studies. He had lifelong episodes of recurrent syncope that occurred due to emotional stress in daily life and pain associated with medical procedures. Since both the head-up tilt and carotid sinus massage tests showed a positive response, he was diagnosed with vasovagal syncope (VVS) and carotid sinus hypersensitivity. He was encouraged to continue the modified tilt training at home, which included leaning on the wall and squatting if leaning was intolerant. Thereafter, syncope was not observed in his daily life. This case highlights the importance of an accurate diagnosis, full education, and home training for recurrent syncope. This case also suggests that the carotid sinus may be involved in the neural network that causes VVS.

Learning objective

Reflex syncope includes both vasovagal syncope (VVS) and carotid sinus syndrome (CSS); however, VVS is discriminated from CSS according to current guidelines. We encountered a case of VVS associated with carotid sinus hypersensitivity. Recurrent syncope disappeared with modified tilt training characterized by conventional tilting and subsequent squatting when tilting was intolerant. This case indicates that the carotid sinus may be involved in the neural network responsible for VVS.

Systemic and cerebral circulatory adjustment within the first 60 s after active standing: An integrative physiological view

Transient cardiovascular and cerebrovascular responses within the first minute of active standing provide the means to assess autonomic, cardiovascular and cerebrovascular regulation using a real-world everyday stimulus. Traditionally, these responses have been used to detect autonomic dysfunction, and to identify the hemodynamic correlates of patient symptoms and attributable causes of (pre)syncope and falls. This review addresses the physiology of systemic and cerebrovascular adjustment within the first 60 s after active standing. Mechanical factors induced by standing up cause a temporal mismatch between cardiac output and vascular conductance which leads to an initial blood pressure drops with a nadir around 10 s. The arterial baroreflex counteracts these initial blood pressure drops, but needs 2-3 s to be initiated with a maximal effect occurring at 10 s after standing while, in parallel, cerebral autoregulation buffers these changes within 10 s to maintain adequate cerebral perfusion. Interestingly, both the magnitude of the initial drop and these compensatory mechanisms are thought to be quite well-preserved in healthy aging. It is hoped that the present review serves as a reference for future pathophysiological investigations and epidemiological studies. Further experimental research is needed to unravel the causal mechanisms underlying the emergence of symptoms and relationship with aging and adverse outcomes in variants of orthostatic hypotension.

Usefulness of Tilt Testing and Carotid Sinus Massage for Evaluating Reflex Syncope

Thirty years ago Tilt Testing (TT) was described as a tool in the diagnostic work-up of vasovagal syncope; after its initial success, some flaws have become evident. The concept of hypotensive susceptibility has provided the test a new relevance, shifting from diagnosis only, to therapeutic management. Carotid Sinus Massage (CSM) was introduced at the beginning of the XX century; the technique has evolved over years, whereas the concept of carotid sinus syndrome (CSS) has remained unchanged and uncontested for more than half a century. Nowadays, CSS is a matter of debate, with new classifications and criteria coming on the scene. Recently, a common central etiological mechanism has been hypothesized for reflex syncope, manifesting as CSS, vasovagal syncope or both. In this context, TT and CSM acquire an important role in clinical practice, being essential for a complete diagnosis and treatment. Recalling their historical background, the present paper illustrates an actual interpretation of TT and CSM.

Syncope: diagnosis and management

Syncope is defined as transient loss of consciousness due to global cerebral hypoperfusion. It is characterized by having a relatively rapid onset, brief duration with spontaneous and full recovery. The major challenge in the evaluation of patients with syncope is that most patients are asymptomatic at the time of their presentation. A thorough history and physical examination including orthostatic assessment are crucial for making the diagnosis. After initial evaluation, short-term risk assessment should be performed to determine the need for admission. If the short-term risk is high, inpatient evaluation is needed. If the short-term risk is low, outpatient evaluation is recommended. In patients with suspected cardiac syncope, monitoring is indicated until a diagnosis is made. In patients with suspected reflex syncope or orthostatic hypotension, outpatient evaluation with tilt-table testing is appropriate. Syncope units have been shown to improve the rate of diagnosis while reducing cost and thus are highly recommended.

Symptomatic presentation of carotid sinus hypersensitivity is associated with impaired cerebral autoregulation

Background

Carotid sinus hypersensitivity (CSH) is associated with syncope, unexplained falls, and drop attacks in older people but occurs asymptomatically in 35% of community‐dwelling elders. We hypothesized that impaired cerebral autoregulation is associated with the conversion of asymptomatic CSH to symptomatic CSH. We therefore conducted a case–control study evaluating individuals with CSH with and without the symptoms of syncope or unexplained falls, as well as non‐CSH controls, to determine whether the blood pressure and heart rate changes associated with CSH are associated with symptoms only when cerebral autoregulation is altered.

Methods and Results

Bilateral middle cerebral artery blood flow velocities (BFV) were measured in consecutive patients with symptomatic CSH (n=22) and asymptomatic controls with (n=18) and without CSH (n=14) using transcranial Doppler ultrasonography during lower body negative pressure‐induced systemic hypotension. Within‐group comparisons revealed significantly lower cerebrovascular resistance index (CVR_i) at nadir for the asymptomatic CSH group (right, mean [95% CI]: 2.2 [1.8, 2.8] versus 2.6 [2.2, 3.0]; P=0.005; left: 2.8 [2.4, 3.3] versus 3.1 [2.7, 3.8]; P=0.016). Between‐group comparisons showed higher mean BFV (right: estimated mean difference, B=5.49 [1.98, 8.80], P=0.003; left: 4.82 [1.52, 8.11], P=0.005) and lower CVR_i (right: B=0.08 [0.03, 0.12], P=0.003, left: B=0.07 [0.02, 0.12], P=0.006) in asymptomatic CSH versus symptomatic CSH groups. There were no significant differences in bilateral mean BFV or right CVR_i between the non‐CSH and symptomatic CSH groups but differences were present for left CVR_i (B=0.07 [0.02, 0.013], P=0.015).

Conclusion

Cerebral autoregulation is altered in symptomatic CSH and therefore appears to be associated with the development of hypotension‐related symptoms in individuals with CSH.

Carotid sinus syndrome: Progress in understanding and management

Carotid sinus syndrome (CSS) is a disease of the autonomic nervous system presenting with syncope, especially in older males who often have cardiovascular disease. The aetiology is unknown and epidemiological data is limited. Forty new patients/million population have been estimated to require pacing for CSS and these patients represent ∼9% of those presenting syncope to a specialist facility. CSS is defined as a response to carotid sinus massage (CSM) that includes reproduction of spontaneous symptoms. Cardioinhibitory CSS shows 3s asystole on CSM and vasodepressor CSS shows >50 mmHg fall in blood pressure (BP), there are mixed forms. The methodology of CSM requires correct massage in the supine and upright with continuous ECG and BP. Assessment of the vasodepressor component implies the ‘method of symptoms’ using atropine to prevent asystole. Carotid sinus hypersensitivity (CSH) is a related condition where CSM is positive in an asymptomatic patient. CSH cannot be assumed to respond to pacing. CSS patients present syncope with little or no warning. If no cause is revealed by the initial evaluation, CSM should be considered in all patients >40 years. CSM carries a small risk of thromboembolism. Therapy for cardioinhibitory CSS is dual chamber pacing, which is most effective in patients with a negative tilt test. Syncope recurrence is ∼20% in 5 years in paced patients. Therapy for the vasodepressor component of CSS, as pure vasodepression or mixed, where tilt testing will likely be positive, is often unrewarding: alternative therapeutic measures may be needed including discontinuation/reduction of hypotensive drugs.

[Experience with the use of an implantable loop recorder in a series of older people with falls and suspected arrhythmic syncopes]

OBJECTIVE

To review our experience on using an implantable loop recorder (ILR) in patients with recurrent falls, when an arrhythmogenic cause is suspected.

MATERIAL AND METHODS

This is a retrospective, observational study of patients with repetitive unexplained falls, suspected syncope, or electrocardiographic abnormalities. All of them had been evaluated by a cardiologist, who decided to implant a loop recorder (ILR) for an accurate diagnosis.

RESULTS

A total of 13 patients received an ILR. The average falls rate for the sample was 3.3. The mean age was 78 years, and 46% were female, with a mean follow-up period of 24 months. During this time, three patients did not suffer from a new fall. An arrhythmogenic diagnosis was obtained in 5 patients: bradycardia was identified in 4 cases, and tachycardia in one of them. The symptoms did not coincide with a documented arrhythmia in the rest of the patients.

CONCLUSION

ILR is a helpful tool to establish an arrhythmogenic cause of unexplained and recurrent falls, in this selected sample of older adults.

Preoperative digital carotid compression as a predictor of the need for shunting during carotid endarterectomy

This study prospectively attempted to assess the need for shunting by preoperative digital compression of the proximal common carotid artery and correlated these findings with intraoperative assessment while performing carotid endarterectomy under local anaesthesia. Preoperative digital compression is highly predictive of the need for shunting intra-operatively and can be used as a valuable test in carefully chosen patients. This may help in decreasing the need for advanced neurological monitoring during carotid endarterectomy.

At the heart of the arterial baroreflex: a physiological basis for a new classification of carotid sinus hypersensitivity

The aim of this review is to provide an update of the current knowledge of the physiological mechanisms underlying reflex syncope. Carotid sinus syncope will be used as the classical example of an autonomic reflex with relatively well-established afferent, central and efferent pathways. These pathways, as well as the pathophysiology of carotid sinus hypersensitivity (CSH) and the haemodynamic effects of cardiac standstill and vasodilatation will be discussed. We will demonstrate that continuous recordings of arterial pressure provide a better understanding of the cardiovascular mechanisms mediating arterial hypotension and cerebral hypoperfusion in patients with reflex syncope. Finally we will demonstrate that the current criteria to diagnose CSH are too lenient and that the conventional classification of carotid sinus syncope as cardioinhibitory, mixed and vasodepressor subtypes should be revised because isolated cardioinhibitory CSH (asystole without a fall in arterial pressure) does not occur. Instead, we suggest that all patients with CSH should be thought of as being 'mixed', between cardioinhibition and vasodepression. The proposed stricter set of criteria for CSH should be evaluated in future studies.

[Long-term follow-up after implantable loop recorder in patients with syncope: results of a French general hospital survey]

BACKGROUND AND OBJECTIVE

Despite recent advances in diagnostic procedures, syncope remains unexplained in 15 to 35% of patients. If implantable loop recorder is a validated diagnostic tool for unexplained syncope, results of this strategy are largely issued from randomized studies. We lack the results of surveys. The aim of this study was to report a single center experience with implantable loop recorders, in patients with unexplained syncope.

METHODS AND RESULTS

A device (Medtronic Reveal DX or XT) was implanted in 31 patients between January 2009 and January 2012. During a mean follow-up of 10.5±8.5 months, loop recording definitively determined that an arrhythmia was the cause of symptoms in 10 patients (32%). Fourteen patients (45%) experienced syncope or pre-syncope. In eight of the 14 patients with syncope, during follow-up, no arrhythmic diagnosis could be made (one patient has been diagnosed as presenting epilepsy and seven as having hypotensive vasovagal syncope). In six patients, the ILR showed an arrhythmic aetiology. Four other patients presented an abnormal ILR result without symptoms. Diagnosis included sinusal arrest in four patients, bradycardia in one patient, advanced atrioventricular block in two patients, ventricular arrythmias in two patients, and supraventricular tachycardia of 180/min in one patient. Therapy was instituted in all patients, in whom an arrhythmic cause was found except one who refused the therapy (six pacemaker, two implantable cardioverter-defibrillator implantations, and one cryoablation of atrioventricular nodal reentrant tachycardia confirmed by an invasive exploration).

CONCLUSION

In this survey, implantable loop recorder implantation led to the diagnosis of an arrhythmic cause in 32% of patients and excluded an arrhythmic cause in 26% of patient with a mean follow-up of 10.5 months.

Hypotensive bradycardic events during shoulder arthroscopic surgery under interscalene brachial plexus blocks

Sudden, profound hypotensive and bradycardic events (HBEs) have been reported in more than 20% of patients undergoing shoulder arthroscopy in the sitting position. Although HBEs may be associated with the adverse effects of interscalene brachial plexus block (ISBPB) in the sitting position, the underlying mechanisms responsible for HBEs during the course of shoulder surgery are not well understood. The basic mechanisms of HBEs may be associated with the underlying mechanisms responsible for vasovagal syncope, carotid sinus hypersensitivity or orthostatic syncope. In this review, we discussed the possible mechanisms of HBEs during shoulder arthroscopic surgery, in the sitting position, under ISBPB. In particular, we focused on the relationship between HBEs and various types of syncopal reactions, the relationship between HBEs and the Bezold-Jarisch reflex, and the new contributing factors for the occurrence of HBEs, such as stellate ganglion block or the intraoperative administration of intravenous fentanyl.

[Significance of diagnostic methods in the work-up of syncope]

After the initial evaluation including detailed history, physical examination, electrocardiogram, and orthostatic blood pressure measurements, risk stratification should follow, if the cause of syncope is still unclear in order to define the acuteness and extensiveness of the further diagnostic evaluation. The documentation of arrhythmia during syncope is the gold standard for diagnosis of arrhythmic syncope. The implantable loop recorder should be integrated early in the diagnostic work-up. In patients >40 years with otherwise unexplained syncope, carotid sinus massage is recommended. In suspected reflex-mediated syncope, the tilt test is able to confirm the diagnosis and gives information about the underlying pathomechanisms, while electrophysiological studies have still a proven indication in patients with previous myocardial infarction and preserved left ventricular function. The adenosine triphophate test has no clinical relevance in the diagnostics of syncope. Echocardiography plays an important role in the risk stratification by diagnosing structural cardiac disease. In patients experiencing syncope associated with exertion, exercise stress testing is indicated. Finally, a coronary angiogram should be performed, if ischemia triggered syncope is suspected. A routinely performed neurological evaluation is not recommended.

[What is new in the 2009 ESC guidelines?]

The 2009 ESC guideline emphasizes active risk stratification and the diagnostic strategy of prolonged ECG monitoring using an implantable loop recorder. The initial evaluation aims at establishing a prima vista diagnosis or at least a diagnostic hypothesis and risk stratification according to ECG criteria and clinical findings. Carotid sinus massage as a diagnostic procedure remains controversial. Electrophysiological study for evaluation of suspected arrhythmogenic syncope is of decreasing relevance. The loop recorder enables documentation of the rhythm during a subsequent syncope. Neurological work-up is not routinely recommended. A standardized evaluation minimizes the rate of unexplained syncopes. Therapeutic decisions include ICD or pacemaker, as indicated in cases of arrhythmogenic syncope or carotid sinus syncope, and mostly general measures in case of other reflex syncopes.

Discrepancy between clinical practice and standardized indications for an implantable loop recorder in patients with unexplained syncope

Aim

An implantable loop recorder (ILR) is indicated in patients with unexplained syncope after complete conventional work-up. Data from the literature imply that, in clinical practice, the ILR is underused. The aim of the study was to verify if there is any discrepancy between the use of ILRs in clinical practice and the potential indications based on the most potentially appropriate guideline indications.

Method and results

We compared the prevalence of ILRs actually implanted in patients with unexplained syncope in the Syncope Unit Project (SUP) study and the potential one using the standard given by the guidelines. In the SUP study, 28 (18%) out of 159 patients with unexplained syncope received an ILR. Appropriate criteria for implantation of ILRs according to guidelines were present in 110 (69%) patients. Moreover, 7 (25%) of ILRs actually implanted did not satisfy the guideline standards. During the follow-up, 32% of patients who had received an ILR had a diagnosis compared with 5% of those who did not (P= 0.001).

Conclusions

The estimated indications were four times higher than those observed. Moreover, in about one quarter of the cases, the use of ILRs proved to be potentially inappropriate according to guideline indications. Two-thirds of patients with unexplained syncope had indications potentially appropriate for ILRs.

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.

Evaluation of sinus and atrioventricular nodes function in patients with vasovagal syncope

AIM

Evaluation of sinus and atrioventricular nodes function as a potential factor responsible for prolonged bradycardia, asystole, or both in patients with cardioinhibitory and non-cardioinhibitory vasovagal syncope (VVS). The study included 258 patients (mean age = 47.7 +/- 17.2 years; range 18-62; 147 females) with a history of VVS. They were divided among four groups, according to results of head-up tilt test (HUTT).

METHODS

All patients underwent standard HUTT, carotid sinus massage (CSM), and rapid transesophageal atrial pacing for evaluation of total sinus node recovery time (SNRT), and corrected sinus node recovery time (CNRT), resting and intrinsic heart rate (IHR), and Wenckebach point (WP). Values of SNRT > 1,500 ms, CNRT > 525 ms, WP < 130 bpm, and CSM-induced pause >3 seconds were considered abnormal.

RESULTS

SNRT, CNRT, and WP before and after pharmacological blockade, resting heart rate, and IHR did not differ significantly among the study groups. The prevalence of mild sinus node dysfunction (SND), decreased value of WP, and cardioinhibitory carotid sinus hypersensitivity was similar among all study groups.

CONCLUSIONS

The prevalence of mild SND, abnormal atrioventricular conduction, and carotid sinus hypersensitivity (CSH) was similar among patients with VVS regardless of the type of vasovagal reaction. SND and CSH do not seem to play an important role in the pathogenesis of cardioinhibitory vasovagal reaction.