The SPEED Protocol: Using Ultrasound To Detect Acute Aortic Dissection

A 59-year-old man presents to your community emergency department (ED) with chest pain that is radiating to his back. His vital signs are normal and the ECG does not demonstrate a myocardial infarction. Your clinical gestalt has you suspecting an acute aortic dissection (AoD). While waiting for laboratory investigations, including troponin and d-dimer, you wonder if a quick point-of-care ultrasound (POCUS) examination looking for three sonographic findings could help determine the likelihood of this being an AoD.

Aortic syndrome (AAS) has been called the lethal triad and includes AoD, intramural hematoma (IMH), and penetrating aortic ulcer.1 It is a deadly but rare condition that can present in atypical ways leading to delays in diagnosis associated with increased mortality.

AoD is broadly classified into two major types according to the Stanford classification system: Type A and Type B. This system is based on the location of the tear and helps guide treatment strategies. Type A dissections involve the ascending aorta and may extend into the descending aorta. It is more common and more dangerous than Type B, as it can lead to serious complications like rupture into the pericardial space leading to cardiac tamponade, aortic valve insufficiency, or myocardial infarction. Type B dissections occur in the descending aorta only, after it has passed the arteries that supply blood to the arms and head. They are less common than Type A and usually less immediately life-threatening, but still serious and potentially fatal if not treated properly.

Speed is important in making the diagnosis of an AoD due to the associated increase in mortality with delays.2,3 There are clinical decision tools available, but the American College of Emergency Physicians does not recommend the routine use of these tools in suspected cases of AoD.4

In patients with a suspected AoD, what is the diagnostic accuracy of three sonographic findings?

Gibbons RC, Smith D, Feig R, et al. The sonographic protocol for the emergent evaluation of aortic dissections (SPEED protocol): A multicenter, prospective, observational study. Acad Emerg Med. 2024;31(2):112-118.

  • Population: A convenience sample of adult patients with clinically suspected Stanford type A or B AoDs before performing a POCUS or CTA from January 2010 to December 2019
    • Excluding: Patients unable to consent, those with a pre-existing or traumatic AoD, and individuals who did not receive a POCUS evaluation before advanced imaging (CTA, MRA, or TEE).
  • Intervention: POCUS performed by PGY1 to three emergency medicine residents to identify three sonographic findings consistent with acute aortic dissection. This included (1) the presence of either a pericardial effusion or (2) an intimal flap, or (3) an aortic outflow track diameter greater than 35 mm measured from the inner wall to the inner wall within 20 mm of the aortic annulus during end-diastole.
  • Comparison: CTA of chest-abdomen-pelvis, MRI/MRA, or cardiology-performed TEE
  • Outcome:
    • Primary Outcome: Diagnostic accuracy of identifying a Stanford Type A and B AoDs
    • Secondary Outcomes: Test characteristics of each of the three individual sonographic findings for diagnosing Stanford type A and B AoDs
  • Type of Study: Multicenter, prospective, observational, cohort study of a convenience sample of adult patients.

The SPEED protocol has an overall sensitivity of 93.2 percent for AoD.

There were 1,314 patients included in the study. The median age was 59 years with 49 percent being female. A total of 44 cases (3.3 percent) were diagnosed with AoD with 21 (1.5 percent) Stanford type A and 23 (1.8 percent) Stanford type B dissections. Additionally, 41 cases (93.2 percent) had at least one finding present on POCUS examination.

While the sensitivity of POCUS for aortic dissection was high, the 95 percent confidence interval around the point estimate was very wide.

  • Primary Outcome: Diagnostic accuracy of identifying Stanford type A and Stanford type B AoDs
  • Secondary Outcomes: Test characteristics of each of the three individual sonographic findings for diagnosing Stanford type A and Stanford type B AoDs.
  1. Convenience Sample: These were not consecutive patients but rather a convenience sample of patients with suspected AoD. This could have introduced selection bias into the study.
  2. Ultrasonographers: POCUS was performed by PGY1–PGY3 emergency medicine residents. They received a four-hour introductory course taught by emergency ultrasound faculty. In addition, each resident completed a three-week emergency ultrasound rotation during their internship. They did not receive any additional formal training before participating in the study except for the standard bedside teaching throughout their residency. This may impact the external validity of the results to attending physicians in a non-academic, community, or rural settings.
  3. Prevalence: The prevalence of 3.5 percent was high compared to previously published data.5,6 This too suggests some selection bias. However, 3.5 percent is still a relatively small number and this results in a wide 95 percent confidence interval around the point estimate for the diagnostic accuracy metrics.

Aortic dissections are rare diagnoses, deadly diagnoses and hard to diagnose even with POCUS.

You perform the SPEED Protocol and do not see any of the three POCUS findings suggestive of AoD. This gives you some reassurance as it lowers the likelihood of this rare and deadly condition. However, the diagnostic accuracy of SPEED is not good enough to fully exclude the diagnosis and you order a CTA to definitively rule out an AoD in this man.

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.

Thank you to Dr. Neil Dasgupta who is an emergency medicine physician and ED intensivist from Long Island, NY for his assistance with this critical appraisal.


William “Ken” Milne, MDDr. Milne is chief of emergency medicine and chief of staff at South Huron Hospital, Ontario, Canada. He is on the Best Evidence in Emergency Medicine faculty and is creator of the knowledge translation project the Skeptics’ Guide to Emergency Medicine (www.TheSGEM.com).

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  2. Erbel R, Aboyans V, Boileau C, et al. 2014 ESC guidelines on the diagnosis and treatment of aortic diseases: Document covering acute and chronic aortic diseases of the thoracic and abdominal aorta of the adult. The Task Force for the Diagnosis and Treatment of Aortic Diseases of the European Society of Cardiology (ESC). Eur Heart J. 2014;35:2873-2926.
  3. Pape LA, Awais M, Woznicki EM, et al. Presentation, diagnosis, and outcomes of acute aortic dissection: 17-year trends from the International Registry of Acute Aortic Dissection. J Am Coll Cardiol. 2015;66(4):350-358.
  4. Diercks DB, Promes SB, Schuur JD, Shah K, Valente JH, Cantrill SV. Clinical policy: critical issues in the evaluation and management of adult patients with suspected acute nontraumatic thoracic aortic dissection. Ann Emerg Med. 2015;65:32-42.
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