n this episode, we review a new clinical policy from the American College of Emergency Physicians (ACEP) on the use of risk stratification tools and D-dimer to exclude non-traumatic thoracic aortic dissection.

Shownotes: FOAMcast.org

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Angioedema = localized swelling of mucous membranes and subcutaneous tissues due to increased vascular permeability.

Triggers increased vascular permeability → fluid shifts into tissues.

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In this episode, Sam Ashoo, MD and T.R. Eckler, MD discuss the December 2024 Emergency Medicine Practice article, Diagnosis and Management of Acute Mesenteric Ischemia in the Emergency Department

Emergency Medicine Residents, get your free subscription by writing [email protected]

Sam Ashoo, MD, FACEP,  is board certified in emergency medicine and clinical informatics. He serves as EB Medicine’s editor-in-chief of interactive clinical pathways and FOAMEd blog, and host of EB Medicine’s EMplify podcast. Follow him below for more…

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Date: September 23, 2024

Reference: Essat et al. Diagnostic Accuracy of D-Dimer for Acute Aortic Syndromes: Systematic Review and Meta-Analysis. Annals of Emergency Medicine, May 2024

Guest Skeptic: Dr. Casey Parker is a Rural Generalist from Australia who is also an ultrasounder.

Case: You are working a busy shift in a rural emergency department (ED) and your excellent Family Medicine trainee presents a case of a 63-year-old woman with chest pain and some intermittent radiation into the inter-scapular region. The patient has no specific risk factors for acute coronary syndrome (ACS) or dissection. The history is not overly concerning for dissection – the adjectives “severe”, and “ripping” or “tearing” are not used.

Your trainee has done a great work-up and the possibility of an acute aortic dissection (AAD) is included in her differential diagnosis. Because this is a rural ED and the closest Computed tomography angiography (CTA) is a three-hour drive away, we must decide if this will benefit this patient.

You accompany your trainee back to the bedside and clarify the nature of the chest pain, re-examine the patient and review all the available clinical data. There are no abnormalities in the blood work, ECG, or chest x-ray. Her pain seems to have settled. In this woman with no specific features of an aortic dissection, can we use a D-dimer assay to rule out this serious diagnosis and avoid a long and costly transfer?

Background: Diagnosing acute aortic syndromes (AAS), which encompass life-threatening conditions like aortic dissection, intramural hematoma, and penetrating ulcers, can be challenging in the emergency department. These conditions typically present with nonspecific symptoms such as chest, back, or abdominal pain, and without early identification, they carry high morbidity and mortality. Aortic dissections are known for their rapid progression and the necessity for swift diagnosis and intervention.

CTA is often the go-to imaging modality due to its high sensitivity and specificity for detecting AAS, but its routine use comes with risks—exposure to ionizing radiation and increased healthcare costs. In low-prevalence populations, over-reliance on CTA may be unwarranted.

Emergency physicians have increasingly turned to the D-dimer test, a readily available blood test, to help rule out AAS and reduce unnecessary imaging. However, the effectiveness of D-dimer for diagnosing AAS remains debated due to variable test performance in different patient populations.

The American College of Emergency Physicians (ACEP) has a policy on thoracic aortic dissections. They asked: “In adult patients with suspected acute nontraumatic thoracic aortic dissection, is a negative serum D-dimer sufficient to identify a group of patients at very low risk for the diagnosis of thoracic aortic dissection?”

Reference: Essat et al. Diagnostic Accuracy of D-Dimer for Acute Aortic Syndromes: Systematic Review and Meta-Analysis. Annals of Emergency Medicine, May 2024

Authors’ Conclusions: “D-dimer concentration has high sensitivity (96.5%) and moderate specificity (56.2%) for acute aortic syndrome, with some uncertainty around estimates due to risk of bias and heterogeneity.”

Quality Checklist for Systematic Review Diagnostic Studies:


Results: The mean age ranged from 53 to 63 years, and studies included a mixed-gender population.

This is very similar to the test characteristic for D-Dimer in the investigation of pulmonary embolism.

Spectrum Bias

1. Disease Spectrum: The studies included patients with “acute aortic syndrome” which is a blanket term including traditional dissection, intramural hematoma and penetrating atherosclerotic ulceration. As a clinician, I am interested in excluding the immediate life threat – that is a type A dissection. By including these other disease entities as “true positives” it may make the sensitivity appear better than it would be if we only counted “acute aortic dissection” as a positive.

This is akin to finding a bunch of sub-segmental pulmonary embolisms (PEs) and grouping them with a few saddle PEs and combining all these as “true positives”. Your test will look more sensitive, but will it detect a disease that may not be clinically important?

2. How Sensitive is Good Enough? To answer this question, we need to consider the badness of the disease, the risks of overdiagnosis and the available interventions. True aortic dissection is a bad disease with high mortality. Surgery is good in these cases with the long-term survival rates in the 80% range. Therefore, we can say this is a disease worth identifying, and we should demand a very high sensitivity to exclude AAD.

This is a subjective call but 96% might not be good enough. For other serious diseases, e.g. a subarachnoid hemorrhage we get up to 99+%. Every clinician and patient will have a different risk tolerance, and they would consider being a sensitive enough test.

Thomas Bayes

3. BAyes – It’s All About the Bayes: The key to diagnostic tests is to have a clear understanding of pre-test probability before applying a test such as a D-dimer. The likelihood ratios presented here are useful: if we know that the -LR is 0.06 and if we decide that we will accept a 1% post-test probability then we can only be happy to use a D-dimer in patients where we have a 20% or less pre-test probability of dissection. That population may be hard to define as it is a clinically dichotomous presentation.

If a patient uses the terms “tearing” or “severe” we are probably already well over that threshold. However, typically we use our gestalt to decide who is so low risk that history and exam are enough to place them in a “go home” group.

4. Imaging Efficiency: The role of D-dimer is to decide who gets a CT and who does not. Unfortunately, this paper shows a wide range of specificities. The pooled specificity in this analysis had specificity in the “coin toss range” and this could result in an increase in imaging with no patient-important benefits.

We have seen examples in the past (e.g. The Canadian Assessment of Tomography for Childhood Head Injury [CATCH]) where such a clinical decision tool increased the imaging without improving outcomes. We just may be shooting ourselves in the foot here. It may be that clinical gestalt is as good to decide who we don’t send the patient to the “donut of truth” (CT scanner). It would require a real-world validation trial to measure the efficiency and patient-oriented outcome (POO) of benefits that D-Dimer may / or may not add in the workup of AAS.

5. Heterogeneity in the Populations: Sometimes just looking at the baseline is all we need to know. When it comes to pre-test probability, we can look at the actual pick-up rates in the study to get a feel for how dilute (prevalence) the disease was in that population. In other words, which patients were considered risky enough to include in each cohort? There is a wide range of prevalence across countries and studies. One Japanese study included 65% of patients with the disease. In contrast, a UK cohort had only a 1% rate of AAS (this was a clear outlier). However, it is important to include all the available trials and not “cherry-pick” with results that seem tight and precise.

Pooling data from these different patient groups is difficult and can make it harder to inform our practice. Our local culture and risk tolerance are likely not represented by many of these trials.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: These numbers are derived straight from the data – so it’s hard to argue. However, I agree with the authors’ discussion points: “It is not clear whether D-dimer is best targeted at low or moderate-risk patients. European guidelines suggest using D-dimer in patients with a low risk of acute aortic syndrome, but this could lead to indiscriminate use of D-dimer in patients at negligible risk and a consequent increase in negative imaging.”

Case Resolution: Clinically your gestalt says that this is not a dissection. You enter a shard-decision-making discussion with the woman and her husband. You let her know that her acute coronary syndrome and pulmonary embolism risks are low and that she has a small but NON-ZERO risk of aortic disease. A blood test called a D-dimer may further lower this risk, however there is a good chance it will return a false positive and muddy the waters. She feels reassured after the counselling and decides not to pursue future investigation and is happy to go home with appropriate instructions about returning if her symptoms return or change.

Dr. Casey Parker

Clinical Application: D-dimer testing is a sensitive but non-specific marker of acute aortic syndromes. It may have a role in the risk stratification of patients with intermediate risk of aortic dissection on clinical assessment. Further study of the real-world outcomes of algorithms using D-dimer is required before we use it as a one-way tool in ED practice.

What Do I Tell the Patient? We are happy to hear that your pain has resolved and at this time we feel that further investigation will not benefit you. Please do not hesitate to return if your symptoms return or if you have other concerns.

Keener Kontest: Last week’s winner was Dr. Michael Zelenetz. He knew the stage name of the singer in the 1999 movie “Bring out the Dead” who was resuscitated with naloxone was I.B. Bangin, otherwise known as Fredrick (not Fred or Freddy) Smith.

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Reference: Gibbons et al. The sonographic protocol for the emergent evaluation of aortic dissections (SPEED protocol): A multicenter, prospective, observational study. AEM February 2024.

Date: February 28, 2024

Guest Skeptic: Dr. Neil Dasgupta is an emergency medicine physician and ED intensivist from Long Island, NY.  He is the Vice Chair of the Emergency Department at Nassau University Medical Center in East Meadow, NY, the safety net hospital for Nassau County.

Case: A 59-year-old man walks into your community emergency department (ED) complaining of chest pain. It is described as a ripping sensation that radiates to his back. His vital signs are all normal and the ECG done at triage does not show an occlusive myocardial infarction. The chest x-ray is unremarkable, and his troponin is not elevated. You suspect an acute aortic dissection (AoD). However, your CT scanner is offline for two hours of scheduled maintenance. He will need to be transferred to the tertiary care center which is 35 minutes away by ground EMS if it is a dissection. Your Spidey senses are tingling, and you don’t want to wait for the CT scanner to be back online to make the diagnosis. Arrangements are made for him to be transferred stat to the tertiary hospital while he is still stable. You wonder if a quick POCUS examination looking for three sonographic findings while waiting for the paramedics could help determine the likelihood of this being an AoD.

Background: We recently covered acute aortic syndrome (AAS) on SGEM#430. AAS has been called the lethal triad and includes aortic dissection (AD), intramural hematoma (IMH), and penetrating aortic ulcer [1]. It is a rare but deadly condition that can present in atypical ways leading to delays in diagnosis and an associated increase in mortality.

This episode is going to focus on acute aortic dissection (AoD) which is 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 Involves the ascending aorta and may extend into the descending aorta. It’s 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. Symptoms may include more severe chest pain radiating to the back, loss of consciousness, or symptoms of stroke if the blood supply to the brain is affected. Type A AoDs generally require an emergent trip to the operating room as soon as they are identified to reduce the likelihood of a terrible outcome.

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. Symptoms can include sudden onset of pain in the back or abdomen, depending on the exact location and extent of the dissection. The pain is often described as tearing or ripping.

Speed is important in making the diagnosis of an AoD due to the associated increase in mortality with delays [2,3]. We know from last week that clinical decision tools (CDTs) are not ready for prime time. This is consistent with the American College of Emergency Physicians (ACEP) which does not recommend the routine use of clinical decision rules in suspected cases of AoD [4].

Reference: Gibbons et al. The sonographic protocol for the emergent evaluation of aortic dissections (SPEED protocol): A multicenter, prospective, observational study. AEM February 2024.

Dr. Ryan Gibbons

This is the first SGEMHOP of 2024. I’m pleased to introduce Dr. Ryan Gibbons. He is a proud graduate of the Lewis Katz School of Medicine (LKSOM) at Temple University where he completed his Emergency Medicine (EM) residency, serving as chief resident, followed by an Advanced Emergency Medicine Ultrasonography (AEMUS) fellowship at Temple as well. Currently, Dr. Gibbons is an Associate Professor of EM, AEMUS fellowship director, and the Director of Ultrasound in Undergraduate Medical Education (UME). 

Authors’ Conclusions: “The SPEED protocol has an overall sensitivity of 93.2% for AoD.”

Quality Checklist for Observational Study:

Results: Over the ten years, 1,314 patients were approached and agreed to be enrolled in the study. The median age was 59 years with 49% being female. There were 21 (1.5%) Stanford type A and 23 (1.8%) Stanford type B dissections diagnosed. Of the 44 (3.3%) cases diagnosed, 41 of them (93.2%) had at least one finding present on POCUS.

Listen to the SGEM podcast to hear Ryan answer our five nerdy questions.

1. Convenience Sample: These were not consecutive patients but rather a convenience sample of patients with suspected AoD. How did patients ultimately make it into the study, and what biases could this have introduced into the sample?

2. Ultrasonographers: These scans were done by PGY1 – PGY3 emergency medicine residents. They received a four-hour introductory course taught by our 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. Do you think this can be extrapolated to an attending physician in a non-academic, community or rural setting?

3. Lack of Masking: Physicians performing the scan were not masked. They also had access to laboratory results (d-dimer) and plain film imaging. How do you think that could have biased the results?

4. Prevalence Higher: Your prevalence of 3.5% was high compared to previously published data [5.6]. This too suggests some selection bias. What other biases could this suggest?

5. Prevalence Sill Low: The 3.5% is still a small number even if it is larger than other published data. This small number of cases results in a wide 95% confidence interval around the point estimate for the diagnostic accuracy metrics. What impact do you think this may have had on your results?

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree with the authors’ conclusions but would have added that there was a wide confidence interval around the reported 93.2% sensitivity.

Case Resolution: The vascular surgeon says to get on the road and don’t wait for the CT scanner to be up and running. Speed is of the essence, and they will be standing by on arrival to assess the patient. The patient arrives alive, and you transfer care to the vascular team. When you get back to the community hospital you find out the CTA shows a Stanford Type B aortic dissection, and the vascular team is discussing the next steps with the patient and their family.

Dr. Neil Dasgupta

Clinical Application: This is an interesting study but would need to be replicated in other clinical settings to see if it could be a fast and accurate way to diagnose AoD.

What Do I Tell the Patient? It looks like the large blood vessel coming off your heart has a tear. This is a serious and potentially deadly condition. We need to get you to the city hospital ASAP. The ambulance is on the way and the vascular surgeons are waiting for you to arrive.

Keener Kontest: Last week’s winner was David Bowden. He knew St. John’s Wort has some evidence for efficacy in the treatment of mild to moderate depression

Listen to the podcast to hear the question for this episode. If you think you know the answer, send an email to [email protected].  The first correct answer will receive a cool skeptical prize.

SGEMHOP: Now it is your turn SGEMers. What do you think of this episode on POCUS for diagnosing AoD? Tweet your comments using #SGEMHOP. What questions do you have for Ryan and his team? Ask them on the SGEM blog. The best social media feedback will be published in AEM.

References:

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