Carotid Sinus Hypersensitivity (CSH) is a condition that commonly manifests as syncope. There are hypersensitive receptors in the carotid sinus, which cause an exaggerated response when they are stimulated, leading to CSH. The place where the internal and external carotid arteries meet to make the common carotid artery is called the carotid sinus (dilated area in the carotid bifurcation); this is a kind of neurovascular structure, which contains baroreceptors ("baro" is the Greek word for pressure or stretch).
The baroreceptors at the carotid sinus shoot neural signals through the glossopharyngeal nerve to the solitary nucleus in the medulla. Increased pressure or stretch sensed via baroreceptors activates the parasympathetic nervous system, with the net effect of vasodilation, bradycardia, and hypotension. Hypotension further eliminates the inhibitory effect of baroreceptors.
However, the objective definition of CSH includes the evolution of 3 seconds or more of cardiac pause "asystole" (cardioinhibitory) or/and a decrease in the systolic blood pressure 50 mmHg "hypotension" or more (vasopressor), while a carotid sinus massage is made regardless of symptoms occurrence (i.e., might fulfill the criteria but be asymptomatic).
The exact cause of CSH is not well understood. However, it is known that CSH incidence increases with aging, as CSH is very unlikely before the age of 50. Furthermore, it is more common in men than in women, especially those with chronic medical conditions (hypertension, coronary artery disease, diabetes, and valvular pathologies). Besides, there is an association between neurodegenerative disorders and CSH, as the prevalence of CSH is increased in patients with Parkinson disease, Alzheimer dementia, and dementia with Lewy bodies. It is hypothesized that there is a degenerative pathology in the medullary autonomic nuclei, which senses baroreceptors' signals resulting in exaggerated response, manifested as hypotension and bradycardia.
The incidence of Carotid sinus hypersensitivity (CSH) in the United States is 35-40 cases/year/million. The incidence increases with age as CSH is found in the elderly population. It is virtually unknown in the younger population. CSH predominates in males more than females (the ratio is 4 to 1).
The worldwide prevalence of CSH is near 30% of unexplained syncope in elderly, and 14% of the nursing home residents, it is worthy to say that there is an overlap between CSH and vasovagal syncope, orthostatic hypotension and other causes of syncope, this makes a margin of error estimating the incidence rate of each condition by its own presenting as a syncope (i.e., multiple etiologies beyond syncope).
The subtypes of CSH occurrence rates are 70% cardioinhibitory, 10% vasopressor, and 20% for mixed type.
The role of baroreceptors is to control the equilibrium of blood pressure and heart rate. The autonomic nervous system receives information via baroreceptors, which are distributed in the carotid sinus, aortic arch, and great blood vessels. This control forms an arc consisted of afferent limb; baroreceptors sense stretch and change of pressure, and send signals through the glossopharyngeal nerve (baroreceptors in the carotid sinus) and vagus nerve (baroreceptors in the aortic arch) to the solitary nucleus of the medulla, which sends signals through the efferent limb; consist of sympathetic (activated if there are a decreased blood pressure or wall stretch) and parasympathetic (activated if there is an increased blood pressure or wall stretch) effects causing:
The exact mechanism behind CSH is not well understood and might be at any point in the previous pathways. However, what seems to be clear is that stretching or mechanical pressure over the carotid sinus overshoots signals resulting in hypotension or bradycardia or both.
It is noted that when CSH is associated with neurodegenerative disorders, there is tau protein hyperphosphorylation and alpha-synuclein accumulation in the medulla on histological examination with special stains and techniques, which might be the reason behind the association between CSH and neurodegenerative disorders.
The medical history of CSH patients might show hypertension, diabetes, coronary artery disease, and neurodegenerative disorders (Parkinson and Alzheimer). Physical exams might be normal except for the clinical manifestations of the previously mentioned disorders.
Symptomatic CSH mainly present with the following:
Signs and Symptoms
It is very important to determine the cause of falls or syncope in the elderly, as it is very likely to miss an important and critical condition (severe aortic stenosis, arrhythmias) or neurologic conditions (seizure or stroke). Such a miss can lead to critical results, especially if the patient has recurrent episodes of syncope while driving, during sea activities (swimming and diving), parachuting, or running heavy machinery. On the other hand, CSH can be asymptomatic and only happens during a carotid massage. It is worthy to re-mention that CSH diagnostic criteria during carotid massage might happen without symptoms.
It was mentioned in the medical literature; that in rare cases of the head and neck tumors, there has been a hyper-response of the carotid sinus to the tumor burden pressing over baroreceptors (the management depends on the primary tumor, stage, age, and prognosis).
Approach syncope by getting the vital signs and assessing for orthostatic hypotension and getting the history of dehydration-induced by coughing, micturition, or by exercise i.e., hypertrophic cardiomyopathy and aortic stenosis. A family history of sudden cardiac death, medical and surgical history (postprandial syncope after gastrointestinal surgery), complete blood count, basic metabolic panel, and fingerstick glucose (hypoglycemia causes unconsciousness) should be obtained. It is also important to have an electrocardiogram (ECG) and, in certain cases, an echocardiogram. Performing a neurologic exam to screen for transient ischemic attack (TIA) or strokes is needed. Tilt table test is also helpful for the diagnosis of vasovagal syncope and orthostatic hypotension. Performing a brain CT-scan or electroencephalogram EEG if the presentation suggests neurologic etiology is helpful as well.
Other diagnostic options can be used (i.e., Holter monitor and cardiac electrophysiologic study). However, the best method to diagnose CSH is via monitored carotid massage (but again, other causes of syncope must be ruled out, and history helps to choose the proper diagnostic option). Non-accidental falls in the elderly following a sudden loss of consciousness must be approached wisely to avoid misdiagnosing and event recurrence.
Massage Technique: With the patient in the supine position, use the second and third fingers over the carotid sinus, which is located anterior to the sternocleidomastoid muscle at the level of the upper border of the thyroid cartilage. First, massage the right carotid sinus as there are a bunch of receptors, and there is greater response than the left, massage for 5 to 10 seconds with a circular motion. If there is no response, switch to left carotid sinus unless it is contraindicated, and if there is asystole for 3 seconds or more and/or a drop in systolic blood pressure 50 mmHg or more, the test is considered positive regardless of symptoms evolution. If the test is not diagnostic may repeat the test with the patient in the upright position or using a tilt-table (prepared emergency equipment and skillful staff must be at the scene of the carotid massage).
Contraindications to carotid sinus massage:
General approach: Educating the patient about CSH and what might trigger an event (explain the events, cardioinhibitory or vasopressor); i.e., avoid tight collar dressing, chiropractic activities around the neck, or manipulation around the carotid sinus besides the control of associated medical conditions (for example hypertension, diabetes, etc.).
CSH can manifest as a syncopal attack that makes it a challenging task to approach it properly, especially when the historical carotid stimulation is not clear in the presentation (in case of sudden neck movement or a rush in blood pressure i.e. the patients will not always mention a carotid stimulation). Here are the most conditions that mimic CSH:
Hence, a proper wide approach not ignoring critical conditions should take place in the diagnosis process, each syncope case must be scanned and examined well, with the proper diagnostic plan and management. Anyway, some of the syncopal cases remain undiagnosed.
The mortality rate of CSH patients is the same as the general population, CSH in itself is not considered dangerous. However, syncope related injuries are what matters for these patients, non-accidental falls or loss of consciousness in serious occasions can result in multiple fractures or intracranial bleeding, especially since many elderly patients are on anticoagulants or/and antiplatelet medication which can result in fatal consequences.
The major complication is non-accidental falls, which might be serious due to the CSH elderly population (taking anticoagulants, osteoporosis, poor candidates for surgical intervention, or high risk for postsurgical complications). Another issue to consider is while performing carotid massage for diagnosis, ignoring good carotid evaluation (excluding bruits and carotid artery stenosis) may evoke a stroke.
Educating the patient about the nature of the disease and its consequences is essential in the management plan, avoid wearing tight collar clothing and minimizing pressure application near the sinus node (i.e., while shaving) is helpful.
It is also mandatory to avoid actions that need full consciousness (driving, running heavy machinery, and performing sea activities i.e., diving or swimming). For driving, it depends on each state's laws, and physicians must report concerning these laws. However, the patient can retain these activities if proper treatment is achieved (pacemaker placement which can eliminate the cardioinhibitory CSH subtype, in this case, the patient can drive after one week of the pacemaker placement), for the vasodepressor subtype stabilizing the blood pressure might help in returning to the previous activities.
CSH is a cause of syncope in the elderly. Physicians must approach syncope wisely. Ruling out life-threatening conditions first is a priority, after that, a monitored carotid massage is allowed (if not contraindicated), management of CSH is directed toward education about the condition and its consequences in the first place not ignoring the patients' activities requiring a full consciousness, treating the symptomatic patient helps continue daily life activities i.e., driving (after a symptom-free period post-management concerning each state's law and the case conditions). The interdisciplinary collaboration between the healthcare team to approach patients presenting with syncope and the highly skilled hands are needed at healthcare facilities to give suitable care because determining the etiology behind syncope helps in decreasing morbidity and mortality rates.
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