BASICS
DESCRIPTION
- The carotid sinus, located at the bifurcation of the internal and external carotid arteries, contains baroreceptors that are responsive to increases or decreases in arterial pressure. It plays 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/or drop in BP.
- In carotid sinus hypersensitivity (CSH), stimulation of one or both carotid sinuses causes an exaggerated baroreceptor response that can result in dizziness or syncope.
- CSH is defined as asystole for at least 3 seconds and/or a drop in systolic BP of at least 50 mm Hg during carotid sinus massage (CSM).
- CSH is generally divided into three subtypes, based on response to CSM:
- Cardioinhibitory (70-75%): asystole for at least 3 seconds
- Vasodepressor (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
EPIDEMIOLOGY
- Disease of elderly; virtually unknown in people aged <50 years
- More prevalent in males by ratio of 4:1
- Typical patient is an older man, usually with a history of coronary artery disease (CAD) and hypertension (HTN), with right CSH > left CSH
- An estimated 35 to 40 patients per million persons per year have CSH complicated by symptoms of dizziness or syncope (1).
- Estimated prevalence of spontaneous CSS is 1%, and induced CSS is 26-60% in elderly patients (2).
ETIOLOGY AND PATHOPHYSIOLOGY
- The exact mechanism of 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 (3).
- 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 (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
RISK FACTORS
- Male gender
- Advanced age
- CAD
- HTN
- DM
COMMONLY ASSOCIATED CONDITIONS
- Sick sinus syndrome
- Atrioventricular block
- CAD
- HTN
- Orthostatic hypotension
- Vasovagal syncope
- Alzheimer disease
- Parkinson disease
DIAGNOSIS
HISTORY
- Recurrent syncope: usually sudden, unexplained, of short duration, seemingly spontaneous, and with complete recovery, although fractures and other injuries may occur
- Unexplained falls: Evidence of a causal relationship is suggested between falls and the cardioinhibitory subgroup.
- Dizziness: Manifests as transient light-headedness or presyncope but not usually as true vertigo; associated more with vasodepressor and mixed subtypes
- Syncope may be associated with prodrome or retrograde amnesia.
- Causative or exacerbating factors
- Any CSM-like maneuver such as shaving, wearing tight collars, or turning one's head sharply
- Neck tumors, extensive neck scarring secondary to radical dissection or radiation fibrosis, and neck trauma
- Certain medications can potentiate symptoms associated with CSH:
- Digoxin or β-blockers (especially with cardioinhibitory subtype)
- Physostigmine, morphine, methacholine: increase vagal sensitivity and may predispose to cardioinhibitory subtype of CSH
PHYSICAL EXAM
Normal unless carotid baroreceptor is stimulated, then
- Bradycardia
- Hypotension
- Pallor
- Diaphoresis
DIFFERENTIAL DIAGNOSIS
- Neurocardiogenic syncope
- Postural hypotension
- Situational syncope
- Postural tachycardia syndrome (POTS)
- Primary autonomic insufficiency
- Hypovolemia
- Dysrhythmias
- Sick sinus syndrome
- Cerebrovascular insufficiency
- Other causes of syncope (e.g., metabolic, psychogenic)
DIAGNOSTIC TESTS & INTERPRETATION
- ECG may demonstrate sinus pause(s) or atrial-ventricular block.
- Carotid duplex scan to rule out carotid stenosis in presence of a bruit (see the following section)
Diagnostic Procedures/Other
CSM is indicated in patients >40 years of age with syncope of unknown etiology after a negative initial evaluation (4)[B]. Commonly accepted technique for accurate diagnosis involves the following steps:
- Patient in supine for 5 minutes with continuous BP monitoring and ECG (on footplate-type tilt table for increased diagnostic accuracy); baseline BP and ECG are recorded.
- For 5 to 10 seconds, apply firm longitudinal massage over the right carotid sinus (between the superior border of the thyroid and the angle of the mandible) at the site of maximal pulsation:
- Note that light pressure over the carotid sinus will not reliably produce a hypersensitivity response.
- Record symptoms, BP, and note ECG changes.
- Discontinue if asystole ≥3 seconds.
- Positive response defined per criteria is listed above (asystole ≥3 seconds and/or drop in BP ≥50 mm Hg); although, specificity of the CSM technique increases if reproduction of a patient's syncope is demonstrated during a test (4)[B]. If nondiagnostic, apply pressure to the left carotid sinus while the patient remains supine; if still nondiagnostic, repeat in 70-degree head-up tilt (first on the right then, if necessary, the left), allowing time for hemodynamic adjustment to the head-up position.
- Evidence behind the testing strategy
- Right side first: Up to 66% with CSH have positive response on the right. If a positive right response, no need to repeat test on the left side.
- 30% of CSM exams are found to be nondiagnostic in the supine position but diagnostic in the 70-degree position (5).
- Positive predictive value increases from 77% to 96% with a specificity of 93% by also performing CSM in 60- to 70-degree tilt position (6).
- Absolute contraindications for CSM testing
- Carotid bruit present: must examine via carotid ultrasound with Doppler first:
- No testing if >70% stenosis
- Supine only testing if 50-70% stenosis
- Myocardial infarction, transient ischemic attack, or stroke within the past 3 months
- Relative contraindications to CSM testing
- History of ventricular tachycardia or ventricular fibrillation
- False-positive results with CSM are relatively common in the elderly. Care should be taken to exclude other causes of syncope (7).
TREATMENT
GENERAL MEASURES
- No treatment is required for asymptomatic individuals.
- High-dietary salt intake and increased fluid intake may be helpful to maintain intravascular volume in patients with vasodepressor subtype and absence of other cardiovascular disease.
MEDICATION
First Line
No single agent has demonstrated long-term effectiveness for treatment of recurrent and symptomatic CSH.
Second Line
- Fludrocortisone or midodrine may be used to improve orthostatic symptoms in patients with vasodepressor subtype (not approved by FDA for this indication). There is risk for supine HTN.
- Atropine may be used in the acute setting in patients with cardioinhibitory subtype with bradycardia.
- Some evidence of benefit from sertraline and fluoxetine in patients unresponsive to pacemakers
SURGERY/OTHER PROCEDURES
- Permanent pacing: treatment of choice for patients with cardioinhibitory and mixed type CSH with recurrent syncope
- Based on American College of Cardiology (ACC)/American Heart Association (AHA)/Heart Rhythm Society (HRS) 2008 guidelines for device-based therapy in CSH
- Class I indication: Permanent pacing is recommended for recurrent syncope caused by spontaneously occurring carotid sinus stimulation and carotid sinus pressure that induces ventricular asystole of >3 seconds (8)[C].
- Class IIa indication: Permanent pacing is reasonable for syncope without clear, provocative events and with a hypersensitive cardioinhibitory response of ≥3 seconds (8)[C].
- Dual-chamber pacing is preferred.
- Permanent pacing is discouraged in patients with a hypersensitive cardioinhibitory response to carotid sinus stimulation in the absence of symptoms.
- Permanent pacing may reduce the frequency of symptoms but may not completely eliminate them.
- Surgery for patients with CSH secondary to mass effect from tumor burden
- Carotid sinus denervation by surgery or radiation therapy is no longer recommended because of the high rate of complications.
ONGOING CARE
PATIENT EDUCATION
- Avoid precipitating maneuvers (as described above) that place pressure on the neck, such as tight collars and neckties.
- With syncope, restrict driving or other potentially hazardous activities until the patient is cleared by the physician (4).
- Avoid precipitating medications like vasodilators and those temporally related to symptoms.
- Teach patient to assume supine position if prodromal symptoms or presyncope occurs.
- Explain diagnosis, provide reassurance, and explain risk of recurrence.
PROGNOSIS
- The presence of CSH has not been demonstrated to confer an independent mortality risk.
- Untreated CSS patients have a syncope recurrence rate as high as 62% within 4 years.
- Patients treated with pacemakers have fewer episodes of syncope but, especially those with mixed CSH, may have a recurrence rate of 16% (1).
REFERENCES
11 Lopes R, Gon §alves A, Campos J, et al. The role of pacemaker in hypersensitive carotid sinus syndrome. Europace. 2011;13(4):572-575.22 Wieling W, Krediet CT, Solari D, et al. At the heart of the arterial baroreflex: a physiological basis for a new classification of carotid sinus hypersensitivity. J Intern Med. 2013;273(4):345-358.33 Tan MP, Chadwick TJ, Kerr SR, et al. Symptomatic presentation of carotid sinus hypersensitivity is associated with impaired cerebral autoregulation. J Am Heart Assoc. 2014;3(3):e000514.44 Moya A, Sutton R, Ammirati F, et al. Guidelines for the diagnosis and management of syncope (version 2009). Eur Heart J. 2009;30(21):2631-2671.55 Parry SW, Richardson DA, O'Shea D, et al. Diagnosis of carotid sinus hypersensitivity in older adults: carotid sinus massage in the upright position is essential. Heart. 2000;83(1):22-23.66 Kapoor JR. Carotid sinus hypersensitivity: a diagnostic pearl. J Am Coll Cardiol. 2009;54(17):1633.77 Kerr SR, Pearce MS, Brayne C, et al. Carotid sinus hypersensitivity in asymptomatic older persons: implications for diagnosis of syncope and falls. Arch Intern Med. 2006;166(5):515-520.88 Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol. 2008;51(21):e1-e62.
ADDITIONAL READING
Seifer C. Carotid sinus syndrome. Cardiol Clin. 2013;31(1):111-121.
SEE ALSO
Syncope
CODES
ICD10
G90.01 Carotid sinus syncope
ICD9
337.01 Carotid sinus syndrome
SNOMED
- Carotid sinus hypersensitivity
- Carotid sinus syncope (disorder)
CLINICAL PEARLS
- Consider CSH as a potential cause for syncope, dizziness, or unexplained falls, especially in the elderly.
- Diagnose CSH via carotid sinus massage (using firm pressure for 5 to 10 seconds), producing asystole of at least 3 seconds and/or a drop in systolic BP of at least 50 mm Hg. (See contraindications discussed earlier before undertaking carotid sinus massage as a diagnostic maneuver.)
- Remember to auscultate for carotid artery bruit prior to considering carotid sinus massage.
- Consider dual-chamber pacemaker in patients with recurrent syncope and cardioinhibitory or mixed CSH subtypes.
- The finding of CSH does not exclude other causes of syncope.