Vascular Causes of Syncope

Author: Brit Long, MD (EM Resident Physician at SAUSHEC; USAF) // Edited by: Alex Koyfman, MD (EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital) and Justin Bright, MD (@JBright2021)

A 36 year-old female presents with chief complaint of “I passed out.” Further questioning reveals one day of pleuritic chest pain with exertional shortness of breath. She has no medical history and takes oral contraceptives. Vital signs are pertinent for heart rate of 102. ECG reveals sinus tachycardia. With her story, a CT chest is done, which reveals several large pulmonary emboli.

A 54 year-old male with a history of hypertension presents with sudden, tearing chest pain. His wife called EMS after he transiently lost consciousness at home. He appears diaphoretic and in distress on your exam. Initial vital signs show a blood pressure of 79/45. Due to his instability, you quickly bring in the ultrasound. EFAST reveals a pericardial effusion with right ventricular collapse during diastole, and suprasternal US shows a proximal aortic dissection.

A 62 year-old female with a history of heart disease, hypertension, and diabetes presents with sudden headache. She states that the headache occurred “out of the blue.” The headache is described as sudden in onset, posterior in location, and maximal at onset. She decided to come to the ED after she experienced an episode of syncope.  Head CT non-contrast reveals a large subarachnoid bleed.

These three patients presented with syncope as part of their respective histories, despite suffering from different pathologies. Syncope is a transient loss of consciousness with rapid recovery to baseline. Each history is concerning for a vascular etiology. In the ED we are focused on risk stratifying and ruling out life threats. Vascular and cardiac causes of syncope are two different pathways that ED physicians must rule out. This post will cover vascular causes of syncope.


Syncope accounts for 2% of ED visits per year and 2-7% of hospital admissions. Anywhere from 12-40% of patients experience one episode of syncope by age forty years, and for patients over age 75 years, the annual incidence of syncope is 6%! (1,2)

The final pathway of syncope results from 10 seconds of complete blood flow and nutrient disruption to the central nervous system, requiring about a 35-50% reduction in cerebral blood flow. Numerous etiologies exist including vasovagal (20-30%), cardiac (10%), orthostatic (10%), medication-related (7%), neurologic (37%), and unknown/idiopathic (37-40%). Even after ED evaluation, upwards of 60% of these patients will have an unknown cause! (3)

Emergency medicine physicians are on the lookout for cardiac causes primarily. We all know to look for arrhythmias such as AV blocks, long QT, WPW, HOCM, Brugada syndrome, and arrhythmogenic right ventricular dysplasia. (3) This post will focus on vascular causes of syncope, which are etiologies we must not miss in the ED. Vascular etiologies are due to obstruction of blood flow to the central nervous system: subclavian steal syndrome, aortic dissection, pulmonary embolism (PE), transient ischemic attack (TIA)/cerebrovascular accident (CVA), intracerebral hemorrhage including subarachnoid hemorrhage, vertebral/carotid dissection, and abdominal aortic aneurysm (AAA).

Subclavian steal refers to flow reversal in the vertebral artery on the same side as significant stenosis or occlusion of the subclavian artery. (4)  The majority of patients are asymptomatic.  In one study only 4.5% of 500 patients presented with symptoms over a 5 year period. (5) When symptoms do occur, they are usually due to arm ischemia: fatigue, pain, paresthesias, or numbness. Syncope can occur with vertebrobasilar ischemia in the setting of concurrent cerebrovascular lesions / atherosclerosis, as well as vertigo, ataxia, diplopia, nystagmus, and dizziness. If a patient presents with syncope and arm symptoms, evaluate pulses in all extremities, evaluate skin and nail beds, and evaluate four limb blood pressures. Evaluation of upper extremity BP will reveal a 15mmHg difference between the normal and affected arms.  If concerned, order US or CT angiography and get in touch with your vascular surgeon. (6)

Aortic dissection occurs with a tear in the aortic intima, with degeneration of the aortic media as a prerequisite. The dissection can propagate distally and/or proximally from the primary tear. (7) This propagation is the primary cause of the clinical symptoms of dissection including ischemia, regurgitation, and tamponade. Most patients tend to be older men (greater than 60 years) with a history of hypertension. However, patients with predisposing conditions such as collagen disorders or inflammatory disorders can be affected earlier in life. (8) If the dissection spreads proximally to include the aortic valve and the pericardium, tamponade can occur and result in syncope. Thus, in patients with syncope who have chest pain, worry about dissection!  Classically, patients present with chest pain that migrates/radiates to the back, or is associated with another symptom below the diaphragm. (7-10) Thus, if a patient has chest pain with syncope, talk to your vascular surgeon. For a more extended discussion, go here:

Not only can aortic dissection present with chest pain and syncope, but so can pulmonary embolism (PE). PE is common and has a wide variety of presentations, including pleuritic pain, cough, shortness of breath, syncope, shock, and sudden death. (11) The most common symptom is dyspnea at rest or exertion (73%), with pleuritic pain in 44%. Patients usually have an acute presentation, but close to 25% may present with gradually worsening symptoms over 1 week. Massive PE with acute right heart failure can result in a large decrease in preload, resulting in reduced stroke volume, hypotension, and syncope due to poor blood flow to cerebral tissue. (11-13) If the patient presents with risk factors (Wells, Geneva, clinical gestalt) with syncope, be concerned about PE. Beyond the standard chest Xray and ECG, use US to evaluate for right ventricular strain!  Be careful of sending the patient whom you have concern of large/massive PE to CT. Use your US, ECG, CXR, and clinical gestalt and call your cardiovascular surgeon and ICU to discuss the patient.

 Cerebrovascular disease is the third leading cause of death in the U.S., and it can result from several different processes including atherosclerosis intrinsic to the vessel, emboli, vascular rupture, or inadequate cerebral blood flow from low perfusion. These patients present with a wide variety of symptoms including paresthesias, cranial nerve deficits, cerebellar deficits, and weakness.  However, patients with obstructive lesions in distal vertebral arteries, cerebellar vascular system, or at the vertebrobasilar junction can present with syncope!  If the patient has syncope in the setting of TIA, the usual source is due to embolism from large vessel or the heart in the setting of arrhythmia. This is a rare presentation with TIA (<5%). (14-19) Ensure these patients receive a full neurologic exam. If the patient presents with any neurologic deficit such as weakness, ataxia, cranial nerve deficits, gait instability, or sensory changes with syncope, be concerned about TIA/CVA.

 Intracerebral hemorrhage accounts for 20% of strokes. Specifically, subarachnoid hemorrhage (SAH) presents as the cause of 50% of these strokes, and these are due to ruptured saccular aneurysms the majority of the time. SAH classically presents as “worst headache of life.”  The onset may be associated with brief loss of consciousness in 53% of patients, nausea/vomiting in 77%, and meningismus in 33%.  Coma is unusual and is a poor prognostic sign. Approximately 30-50% of patients present with sudden, severe headache that precedes a major SAH by 5-20 days. Diagnosis is completed with CT head non-contrast, which has high sensitivity and specificity within six hours of headache onset. Lumbar puncture is usually the next step if head CT is negative, though this is under debate. (19-22) Ultimately, ask about headache in a syncope patient!  If the patient presents with a sudden, severe, maximal in onset headache and syncope, be concerned about SAH and be ready to head down the head CT/LP route. For a more detailed discussion, go here: and

 Carotid/Vertebral Dissection results from separation of arterial wall layers, resulting in production of a false lumen. This false lumen can cause stenosis or formation of thrombi that can embolize distally. Symptoms usually result from thromboembolism. However, local symptoms from compression of adjacent nerves can affect cranial nerves and/or local structures.  Head or neck pain is the most common symptom (up to 90%). The etiology is most commonly due to minor head trauma. Significant dissection can cause hypoperfusion or production of large emboli, resulting in decreased blood flow to the central nervous system. This can lead to syncope. (23-26) Thus, in patients with minor trauma with head/neck pain and syncope, be suspicious of carotid/vertebral dissection. CT angiography is the imaging test of choice.  Go here for a more extensive discussion:

 Abdominal aortic aneurysm (AAA) is an abnormal dilation of the abdominal aorta, most commonly infrarenal in location. An infrarenal aorta greater than 3.0cm in diameter is required for diagnosis. Smoking, male gender, older age, atherosclerosis, and family history of AAA are risk factors. Most patients are asymptomatic. When patients do have symptoms, they often present with abdominal, back, or flank pain.  However, only 5-22% of patients have symptoms if the AAA does not rupture. If the aorta ruptures due to weakening of the wall, patients present with a variety of symptoms, most commonly pain, but syncope can be a presenting complaint. Misdiagnosis is extremely common (MI, perforated viscus, diverticulitis, ischemic colitis, renal stone, etc.).  The classic triad of acute pain, pulsatile abdominal mass, and hypotension only presents in 50% of patients!  The AAA that ruptures into the retroperitoneum often will tamponade, allowing vital signs to normalize and pain to improve. Due to vagal stimulation and lack of blood flow to the cerebral tissue in the setting of immediate rupture, upwards of 15% of patients may present with syncope! (27-29) In the older patient with abdominal pain and/or syncope, establish your IV access and obtain a quick bedside US of the aorta. This US can quickly change management and save the patient’s life if an aneurysm is found.  For a more detailed discussion, go here:


Syncope ultimately results from lack of cerebral perfusion and has multiple causes. Vascular etiologies cause decreased blood flow from obstruction or embolism, decreasing oxygen and nutrient supply to the brain, resulting in syncope.

If your patient presents with…

  1. Symptoms of arm ischemia or paresthesias with syncope – Subclavian steal syndrome
  2. Chest pain that is acute, radiates, tearing/sharp, involves symptoms above and below diaphragm with syncope – Aortic dissection
  3. Tachypnea, pleuritic chest pain, shortness of breath with syncope – PE
  4. Neurologic deficit with syncope – TIA/stroke
  5. Headache that is sudden in onset, maximal at onset, worst of life with syncope – Subarachnoid hemorrhage
  6. Minor trauma with head or neck pain and syncope – Carotid/vertebral artery dissection
  7. Abdominal/flank pain in older patient with syncope – Ruptured AAA

References/Further Reading

  1. Blanc JJ, L’Her C, Touiza A, Garo B, L’Her E, Mansourati J: Prospective evaluation and outcome of patients admitted for syncope over a 1-year period. Eur Heart J 23: 815, 2002.
  2. Quinn JV, Stiell IG, McDermott DA, Sellers KL, Kohn MA, Wells GA: Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes. Ann Emerg Med 43: 224, 2004.
  3. Soteriades ES, Evans JC, Larson MG, et al: Incidence and prognosis of syncope. N Engl J Med 347: 878, 200.
  4. Fisher, CM. A new vascular syndrome: “The subclavian steal.” N Engl J Med 1961; 265:912.
  5. Aboyans V, Criqui MH, McDermott MM, et al. The vital prognosis of subclavian stenosis. J Am Coll Cardiol 2007; 49:1540.
  6. Labropoulos N, Nandivada P, Bekelis K. Prevalence and impact of the subclavian steal syndrome. Ann Surg 2010; 252:166.
  7. Pacini D, Di Marco L, Fortuna D, et al: Acute aortic dissection: epidemiology and outcomes. Int J Cardiol August 7, 2012.
  8. Hagan PG, Nienaber CA, Isselbacher EM, et al: The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA 283: 897, 2000.
  9. Ramanath VS, Oh JK, Sundt TM, et al: Acute aortic syndromes and thoracic aortic aneurysm. Mayo Clin Proc 84: 465, 2009.
  10. Klompas M: Does this patient have an acute thoracic aortic dissection? JAMA 287: 2262, 2002.
  11. White RH: The epidemiology of venous thromboembolism. Circulation 107: I4, 2003.
  12. Roy PM, Colombet I, Durieux P, et al: Systematic review and meta-analysis of strategies for the diagnosis of suspected pulmonary embolism. BMJ 331: 259, 2005.
  13. Courtney DM, Kline JA, Kabrhel C, et al: Clinical features from the history and physical examination that predict the presence or absence of pulmonary embolism in symptomatic emergency department patients: results of a prospective, multicenter study. Ann Emerg Med 55(4): 307, 2010.
  14. Lloyd-Jones D, Adams RJ, Brown TM, et al: Heart disease and stroke statistics 2010 update: a report from the American Heart Association. Circulation 121: e46, 2010. Epub Dec. 17, 2009.
  15. Adams HP Jr, del Zoppo G, Alberts MJ, et al: Guidelines for the early management of adults with ischemic stroke: a guideline from the American Heart Association/American Stroke Association Stroke Council, Clinical Cardiology Council, Cardiovascular Radiology and Intervention Council, and the Atherosclerotic Peripheral Vascular Disease and Quality of Care Outcomes in Research Interdisciplinary Working Groups: the American Academy of Neurology affirms the value of this guideline as an educational tool for neurologists. Stroke 38(5): 1655, 2007.
  16. Goldstein LB, Simel DL: Is this patient having a stroke? JAMA 293(19): 2391, 2005.
  17. Brandt T, Steinke W, Thie A, et al: Posterior cerebral artery territory infarcts: clinical features, infarct topography, causes and outcome. Multicenter results and a review of the literature. Cerebrovasc Dis 10(3): 170, 2000.
  18. Savitz SI, Caplan LR: Vertebrobasilar disease. N Engl J Med 352(25): 2618, 2005.
  19. Al-Shahi R, White PM, et al: Subarachnoid hemorrhage. BMJ 333: 235, 2006.
  20. Linn FHH, Wijdicks EFM, van der Graaf Y, et al: Prospective study of sentinel headache in aneurismal subarachnoid hemorrhage. Lancet 344: 590, 1994.
  21. Edlow JA, Caplan LR: Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med 342: 29, 2000.
  22. Farzad A, Radin B, Oh JS, et al: Emergency diagnosis of subarachnoid hemorrhage: an evidence-based debate. J Emerg Med 44: 1045, 2013.
  23. Schievink WI: Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med 344(12): 898, 2001.
  24. Silbert PL, Mokri B, Schievink WI: Headache and neck pain in spontaneous internal carotid and vertebral artery dissections. Neurology 45(8): 1517, 1995.
  25. Arnold M, Bousser MG, Fahrni G, et al: Vertebral artery dissection presenting findings and predictors of outcome. Stroke 37: 2499, 2006.
  26. Grau AJ, Buggle F: A systematic review of the risk factors for cervical artery dissection. Stroke 36(11): 2340, author reply 2340, 2005.
  27. Lederle FA, Simel DL: The rational clinical examination. Does this patient have abdominal aortic aneurysm? JAMA 281: 77, 1999.
  28. Emergency ultrasound imaging criteria compendium. Ann Emerg Med 48: 487, 2006.
  29. Lederle FA, Johnson GR, Wilson SE, et al: The Aneurysm Detection and Management Study Screening Program: validation cohort and final results. Arch Intern Med 160: 1425, 2000.

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