Carotid Sinus Hypersensitivity
- The carotid sinus is located near the bifurcation of the internal and external carotid arteries and contains baroreceptors that are responsive to increases or decreases in arterial pressure.
- The carotid sinuses play a central role in blood pressure (BP) homeostasis.
- An endogenous increase in BP or external pressure applied to a carotid sinus causes an increase in the baroreceptor firing rate and activates vagal efferents and/or inhibits the sympathetic discharge to the heart and blood vessels, resulting in a slowing of the heart rate and drop in BP.
- In carotid sinus hypersensitivity (CSH), stimulation of one or both carotid sinuses, such as mechanical forces with turning neck) causes an exaggerated baroreceptor response that can result in dizziness or syncope.
- There are three definitions for CSH (1):
- Standard criteria: a pause in heart rate of ≥3 seconds in response to carotid sinus massage (CSM) and/or vasodepression of ≥50 mm Hg drop in systolic BP or both of the above
- Krediet criteria: a pause in heart rate of ≥6 seconds in response to CSM and/or a fall in MAP to a value <60 mm Hg for ≥6 seconds
- Kerr criteria: a pause in heart rate in response to CSM >95th percentile of the population response (7.3 seconds asystole), and/or vasodepression in response to CSM >95th percentile of the population response (>77 mm Hg fall in systolic BP), or both
- CSH is generally divided into three subtypes, based on response to CSM:
- Cardioinhibitory (70–75%): asystole for at least 3 seconds
- Vasodepressive (5–10%): fall in systolic BP of at least 50 mm Hg
- Mixed (20–25%): combination of the first 2 subtypes
- Carotid sinus syndrome (CSS) typically (but not consistently) refers to CSH with syncope and may be classified as:
- Spontaneous CSS: syncope after accidental mechanical manipulation (trigger) of the carotid sinuses (e.g., shaving, tight collars, or tumors)
- Induced CSS: syncope diagnosed by CSM although no mechanical trigger is found
- Disease of elderly; most often occurs in male patients >65 years.
- Associated with a history of coronary artery disease (CAD) and hypertension (HTN), with right CSH > left CSH
- In 2006, CSH was found in 39% of unselected adults >65 years of age using standard diagnostic criteria, and found to be comparable with 2019 review of prevalence data (2).
- CSH may be a cause of the symptoms in 30% of elderly patients with unexplained syncope.
Etiology and Pathophysiology
- The exact site of the abnormality that causes hypersensitivity response in patients with CSH remains unknown. Changes in any part of the reflex arc or the target organs may give rise to this condition, or it may be a part of a generalized autonomic disorder associated with autonomic dysregulation.
- Associated with resting sympathetic overactivity and increased baroreflex sensitivity
- Bradycardia and asystole seen in cardioinhibitory and mixed CSH subtypes appear to be mediated by vagal efferents, whereas vasodilatation and arterial hypotension in the vasodepressor and mixed subtypes are attributed to decrease sympathetic tone.
- Symptomatic CSH has been shown to be associated with impaired cerebral autoregulation, and in asymptomatic CSH, it was found to be normal.
- Atherosclerosis may diminish carotid sinus compliance, resulting in a reduction in afferent impulse traffic in the baroreflex pathway (3).
- CSH is often idiopathic but can be caused by:
- Carotid body tumors
- Inflammatory and malignant lymph nodes in the neck
- Extensive scarring from prior neck surgery in the area of the carotid sinus
- Metastatic cancer
- Advanced age, male gender
Commonly Associated Conditions
- Carotid sinus syncope, sick sinus syndrome
- Atrioventricular block
- Orthostatic hypotension
- Vasovagal syncope
- Alzheimer disease
- Parkinson disease
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