Aortic Dissection

Thoracic Aortic Dissection

A difficult to diagnose, uncommon, and potentially fatal condition: Emergency Medicine at its finest!

 

Let’s talk about a patient we think see every day in the ED. A man comes in complaining of chest pain with elevated blood pressure of 200/90 upon triage. The ECG shows sinus bradycardia with inferior and lateral T-wave inversions. The CXR and troponin are unremarkable. The patient is low risk for PE, and there is no pneumothorax or pneumonia, so this patient is an easy disposition to either home or observation unit depending on whether you want to “rule out ACS”, right?

 

WRONG. Unfortunately, not all chest pain is ACS.

 

This case in detail:

A 51 year-old male presented with chest pain (“tightness”) radiating to the back, which started a few hours prior to arrival, sudden in onset, associated with diaphoresis, dyspnea, and abdominal pain. He has a past medical history of HTN and DM and is an active smoker and former heroin user. He was in mild respiratory distress with HR 56, RR 18, BP 211/92, T 97.8, SpO2 99% on room air.

 

Initial problem list:

Chest pain with dyspnea, abdominal pain, and elevated blood pressure

 

Initial interventions: Monitor, IV catheter x 2, enalaprilat 1.25mg IV, nitroglycerin 400mcg SL; ECG and bedside US

 

Examination:

A obese patient who appears uncomfortable with mild respiratory distress

– Decreased air movement and wheezing, normal heart sounds, no murmur, normal bilateral pulses

– No abdominal tenderness

– 5/5 strength in all extremities

 

ECG: Non-specific T wave inversions

Bedside US: Normal lung sliding, no pericardial effusion, normal EF, and no B lines, normal aortic root

 

The differential diagnosis at this point (after excluding some conditions with bedside sono) included the “badness” of chest pain (acute coronary syndrome, pulmonary embolism, pneumothorax, aortic dissection, esophageal rupture) as well as pneumonia, acute pulmonary edema, myopericarditis, perforated peptic ulcer, or musculoskeletal pathology. Lab testing was notable for anemia of 10.1 with a normal troponin and BNP. A chest xray showed no consolidation or pneumothorax and no widened mediastinum. Given the high suspicion for dissection, a thoracic and abdominal CTA was obtained – this showed a Type B dissection of the thoracic and abdominal aorta from the left subclavian artery to the renal arteries without leak or obstruction of the arterial branches.

 

Dissection Basics: Pathophysiology, Presentation, Diagnosis, and Treatment

 

Pathophysiology

First, let’s talk briefly about the pathophysiology. Aortic dissection is one category of the acute aortic syndrome that includes aortic dissection, intramural hematoma, penetrating atherosclerotic ulcer, and iatrogenic damage to the intima (ie. from an intravascular procedure). A dissection is a tear in the intimal layer of the aorta followed by a progressive extension of the intramural/subintimal hematoma.

There are two basic types, divided by their method of treatment: Type A (involving the ascending aorta), and Type B (not involving ascending aorta). Dissections are most common in people aged 50-65 with smoking and hypertension being risk factors. Other risk factors include connective tissue diseases, cocaine use, vasculitis, aortic coarctation, prior cardiac surgery, and a bicuspid aortic valve, especially when this is associated with a dilated ascending aorta.

  

Presentation

As Dr. Tejani, one of our excellent pediatrics attendings would say, “The eye cannot see what the mind does not know,” and it rings particularly true here. This diagnosis is missed in up to 38% of first presentations, and in 28% of deaths dissection was discovered at post-mortem examination.[i] This is an uncommon diagnosis, with about 8,000 cases per year in the US (~15 cases/100,000 person-years)[ii], and myocardial infarction is approximately 30 times more common (440 cases/100,000 person-years). Much of the data about aortic dissection comes from the IRAD (International Registry of Acute Aortic Dissection).

 

Diagnosis

In general, if you have a patient with chest pain, you should ask them about other associated symptoms. If you find signs or symptoms of ischemia in organs supplied by the branches off of the aorta, this should raise your concern:

There is an aortic dissection detection score from 0 to 3 which has been proposed to risk stratify patients, similar to the Wells score in PE:

Ideally this score would be used to risk stratify your patients into a low, medium, and high-risk category. However, this is based upon retrospective data of patients who were already diagnosed with a dissection, so it does not allow for a sensitivity and specificity analysis. Also, realistically, if someone only complains only of abrupt onset chest pain, they automatically fall out of the low-risk ADD score of 1 and require further testing which makes this score less useful.

 

History and Exam

Lets look at history, exam, and imaging findings more closely. There are four papers summarizing the presence of physical exam and imaging findings suggestive of a dissection. The first two are a set of papers from the IRAD database from 2000 and 2009, which examined the clinical features of dissections. The third is a prospective trial in 2000 done by von Kodolitsch et al with a suspicious patient selection (started with over 40,000 patients and only 250 qualified for their study on “undifferentiated chest pain”). And the fourth was a JAMA paper from 2002 by Klompas in which he created summary likelihood ratios and sensitivity measures from raw data from papers with this raw data.[vi] The major findings are as follows:

Finding % Reporting from 2000 & 2009 IRAD Data 1,[iv] OR from von Kodolitsch study 2000 [v] LR from Klompas study 2000[vi]
Any pain 95.5%
Chest pain 72.7% 1.36 1.6
Abdominal pain 29.6% 2
      ONLY abd pain 4.6%
Tearing or ripping pain 27 1.2-10.8
Pulse deficit 30% (significantly increased mortality if >1 deficit) 75

(BP or pulse differentials)

5.7
CVA/neurologic deficit 4.7% 1 6.6-33
Syncope 13%

(higher mortality, assoc with Type A, tamponade, stroke – OR 3 to 5)

Aortic regurgitation murmur 31.6% 2.12 1.4
CHF 6.6%
Hypertension 49% 1.56
Hypotension/Shock 8% 2.18
ECG with ST/T changes 41.4%
Widened mediastinum on CXR 61.6% 11 2
Normal CXR 12.4%

Of note, there is also a Chinese database, which in 2014, showed dissections in fewer patients with a history of HTN, and a significantly greater percentage of patients presenting with back pain compared to chest pain (77% vs 17%). This may possibly due to the population difference.[vii]

 

Chest X-Ray

After initial vitals, history, and physical exam, there are few lab tests that have proven useful for significantly increasing or decreasing your pre-test probability of having a dissection. Chest xray is a commonly cited imaging modality, however up to 13% of dissections have a totally normal chest xray, with up to 40% of dissections having no widened mediastinum, the classic finding.4 The most suggestive finding of aortic disease on a CXR is aortic kinking or tortuosity, with an odds ratio of 10.2.[viii]

 

D-Dimer

D-dimer has been proposed as a possible rule-out test, much like it is used in PE. However, there is conflicting data on this as well. In the 2016 JAMA systematic review, there was a large range of sensitivities and specificities (sens 51-100%, spec 32-89%)[ix]. A 2016 meta-analysis of d-dimer for acute aortic syndromes (including intramural hematoma and aortic ulcer) showed a sensitivity of 95% and specificity of 60% with at +LR 2.4 and -LR of 0.079.[x] This was based on 12 case-control and cohort studies, and the results were similar when only using 3 of the highest quality studies – no prospective study has been done. ACEP guidelines from 2014 give a level C recommendation that d-dimer should NOT be used as a rule-out test. There is, however, some early work suggesting that when combined with the use of the ADD score (similar to the way wells plus a d-dimer are used in PE), this tool could be used to rule out a dissection. In a Bayesian analysis based on meta-analysis data (yes, this is all very theoretical and statistical), a negative d-dimer with a low (ADD 0) or intermediate (ADD 1) risk patient was associated with a 0.24% and 3.4% risk of dissection respectively.[xi] This has potential!

 

Ultrasonography

Trans-thoracic ultrasound has a sensitivity of 73-100% and a specificity of 71-91%, and is a grade IC recommendation to be performed in the initial evaluation. [viii] Additionally, there is a suprasternal view which you can particularly visualize the aortic arch and look for an intimal flap or dilatation (see figure below). Trans-esophageal echo can be used, especially in patients who are too unstable to be transported for further imaging, with a sensitivity of 86-100% in the JAMA systematic review. The TTE was done looking for presence of intimal flap/intramural hematoma (direct signs of AD), ascending aorta dilatation, aortic valve insufficiency or pericardial effusion/tamponade (indirect signs of AD). Most importantly I think that this test can rule IN dissection – any positive US finding had a specificity of 94% and when combined with an ADD>1 this increased to 96%, possibly allowing early interventions before confirmatory imaging.[xii]

CT

The definitive diagnosis can be made using a CT angiogram of the thoracic and abdominal aorta in a clinically stable patient (sens 100%, spec 100%)[viii]; CTA is equally as effective is trans-esophageal echo in the unstable patient.

 

Distractors are important to recognize. A positive cardiac marker can lead you to think that this patient is having acute MI, when in reality the coronary arteries are being hypoperfused because of the dissection (see image above). Acute ECG changes are present in only 50% of Type A dissections, making this a very non-specific or sensitive tool. New onset CHF is seen in up to 33% of dissections (and even 21% of Type B dissections!) and is associated with a significant delay to surgical management (13 vs 8 hrs).[xiii] Also, patients can have pseudohypotension – a phenomenon in which the blood pressure is being taken from an extremity or vessel which has restricted flow from the dissection, giving a falsely low BP when the patient is actually hypertensive.

 

The European Society of Cardiology (ESC) and American Heart Association (AHA) have released similar algorithms for the evaluation for dissection based on a stable vs unstable and then low vs high risk category based on ADD. I think this is close to what most ED physicians do currently – with the exception of the d-dimer in the ESC recommendations – and likely using more clinical gestalt as compared to the ADD score:

 

Treatment

This is a serious medical emergency, especially for type A dissections involving the ascending aorta. In untreated type A dissections, there is an estimated 1-2% mortality rate per hour for the first 48 hours, with an 80% mortality rate at 2 weeks based on a 2000 epidemiological study.[xiv]

Unfortunately, while there is much consensus on acute treatment there is a lack of actual data. Pain control should be initiated using morphine in these patients, as their pain can cause increased heart rate and blood pressure, two things that may worsen dissections.

 

The general consensus is to use a beta-receptor antagonist initially to control the heart rate and decrease the shearing forces (dP/dT). Esmolol is a short-acting, titratable, mostly beta-1-blocker –  start with a bolus of 500mcg/kg and starting a drip of 50-200mcg/kg/min. Labetalol is another option with alpha-1, beta-1, and beta-2 activity and a longer half-life, given as a 10+20mg IV push repeated every 10 minutes up to 300mg. Labetalol can be a great option in patients who are markedly hypertensive and in whom you are worried about dissection while they are awaiting their imaging studies. The goals of IV vasoactive and chronotropic agents also vary, with the ESC recommending to “reduce the heart rate and lower the systolic BP to 100-120mmHg”[xv] using an IV beta-blocker infusion. After the heart rate is controlled, blood pressure management becomes important. Suggested agents are nicardipine and nitroprusside, with the latter only to be used after beta blocker initiation to prevent reflex tachycardia. The AHA guidelines generally agree with this as well, suggesting initiation with short-acting beta blocker (or calcium channel blocker if contraindication exists to beta-blocker) for titration of heart rate to 60-80 followed by blood pressure control using nitroprusside or nicardipine.[xvi]

 

Definitive treatment of a dissection varies depending on the location of the lesion. A Type A dissection requires immediate surgical management given the high mortality and proximity to great vessels and pericardium. Type B is best treated medically or with open or endovascular repair if there is shock, end-organ ischemia, leaking or rupture, aortic dilatation, or continued pain. If surgery is delayed in a Type A dissection, morality increases from 14% to 67%.15 An RCT comparing endovascular repair and medical management of uncomplicated type B dissections showed no dissection-related deaths in either group but improved “favorable aortic remodeling” (false lumen thrombosis and no dilatation or rupture) in the endovascular group (97% vs 43%, p<0.001).[xvii]

 

Patient course

After the Type B dissection was diagnosed in this patient, the patient was given additional opioid analgesia and started on an esmolol drip an an arterial line was placed. The patient was then started on a nitroprusside drip, given that he was already slightly bradycardic, and blood pressure remained elevated despite esmolol. Once systolic blood pressures were between 90 and 120, he was transitioned to a labetalol drip and admitted to the ICU. During his inpatient course, repeat CT showed a stable lesion. He was discharged on HD #3 on multiple antihypertensive medications and scheduled for endovascular surgery.

 

Take home points

  • Think about it! – You can’t diagnose this if you don’t think about it.
  • Chest pain does not always mean “ACS,” even with a positive troponin. Think: Why is this NOT dissection?
  • Any pain with highly suggestive symptoms should prompt further testing, especially if it is tearing or ripping pain or associated with pulse or neurological deficits.
  • Ultrasonography is a good screening tool – always scan the abdominal aorta and try the suprasternal view!
  • If you’re in a diagnostic dilemma, consider falling back on the combnination of Aortic Dissection Detection score, bedside ultrasonography, and d-dimer to help increase or decrease your pre-test probability before a CTA.
  • Be quick – this can kill quickly:
    • CTA diagnosis, surgical consultation, BP and HR control with vasoactive medications (esmolol until HR<60 then nicardipine or nitroprusside until SBP<120), invasive BP monitoring, ICU admission

 

See also this prior post by a pharmacist colleague in “Pharm to Table”:

Acute Management of Aortic Dissections – A Pharmacologic Approach

 

REFERENCES

[i] Tsai TT, Trimarchi S, Nienaber CA. Acute aortic dissection: perspectives from the International Registry of Acute Aortic Dissection (IRAD). Eur J Vasc Endovasc Surg. 2009 Feb;37(2):149-59.

[ii] Landenhed M, Engström G, Gottsäter A, et al. Risk profiles for aortic dissection and ruptured or surgically treated aneurysms. J Am Heart Assoc. 2015;4(1):e001513.

[iii] Rogers AM, Hermann LK, Booher AM, Nienaber CA, Williams DM, Kazerooni EA, Froehlich JB, O’Gara PT, Montgomery DG, Cooper JV, Harris KM, Hutchison S, Evangelista A, Isselbacher EM, Eagle KA; IRAD Investigators. Sensitivity of the aortic dissection detection risk score, a novel guideline-based tool for identification of acute aortic dissection at initial presentation: results from the international registry of acute aortic dissection. Circulation. 2011 May 24;123(20):2213-8.

[iv] Hagan PG, Nienaber CA, Isselbacher EM, Bruckman D, Karavite DJ, Russman PL, Evangelista A, Fattori R, Suzuki T, Oh JK, Moore AG, Malouf JF, Pape LA, Gaca C, Sechtem U, Lenferink S, Deutsch HJ, Diedrichs H, Marcos y Robles J, Llovet A, Gilon D, Das SK, Armstrong WF, Deeb GM, Eagle KA. The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA. 2000 Feb 16;283(7):897-903.

[v] von Kodolitsch Y, Schwartz AG, Nienaber CA. Clinical prediction of acute aortic dissection. Arch Intern Med. 2000 Oct 23;160(19):2977-82. PubMed PMID: 11041906.

[vi] Klompas M. Does this patient have an acute thoracic aortic dissection? JAMA. 2002 May 1;287(17):2262-72.

[vii] Wang W, Duan W, Xue Y, Wang L, Liu J, Yu S, Yi D; Registry of Aortic Dissection in China Sino-RAD Investigators.. Clinical features of acute aortic dissection from the Registry of Aortic Dissection in China. J Thorac Cardiovasc Surg. 2014 Dec;148(6):2995-3000.

[viii] von Kodolitsch Y, Nienaber CA, Dieckmann C, Schwartz AG, Hofmann T, Brekenfeld C, Nicolas V, Berger J, Meinertz T. Chest radiography for the diagnosis of acute  aortic syndrome. Am J Med. 2004 Jan 15;116(2):73-7.

[ix] Mussa FF, Horton JD, Moridzadeh R, Nicholson J, Trimarchi S, Eagle KA. Acute Aortic Dissection and Intramural Hematoma: A Systematic Review. JAMA. 2016 Aug 16;316(7):754-63.

[x] Watanabe H, Horita N, Shibata Y, Minegishi S, Ota E, Kaneko T. Diagnostic test accuracy of D-dimer for acute aortic syndrome: systematic review and meta-analysis of 22 studies with 5000 subjects. Sci Rep. 2016 May 27;6:26893.

[xi] Baez AA, Cochon L. Improved rule-out diagnostic gain with a combined aortic dissection detection risk score and D-dimer Bayesian decision support scheme. J Crit Care. 2017 Feb;37:56-59.

[xii] Nazerian P, Vanni S, Castelli M, Morello F, Tozzetti C, Zagli G, Giannazzo G, Vergara R, Grifoni S. Diagnostic performance of emergency transthoracic focus cardiac ultrasound in suspected acute type A aortic dissection. Intern Emerg Med. 2014 Sep;9(6):665-70.

[xiii] Vagnarelli F, Corsini A, Lorenzini M, et al. Acute heart failure in patients with acute aortic syndrome. Eur J Heart Fail. 2015;17(9):917-924.

[xiv] Mészáros I, Mórocz J, Szlávi J, Schmidt J, Tornóci L, Nagy L, Szép L. Epidemiology and clinicopathology of aortic dissection. Chest. 2000 May;117(5):1271-8.

[xv] Erbel R, Aboyans V, Boileau C, Bossone E, Bartolomeo RD, Eggebrecht H, Evangelista A, Falk V, Frank H, Gaemperli O, Grabenwöger M, Haverich A, Iung B, Manolis AJ, Meijboom F, Nienaber CA, Roffi M, Rousseau H, Sechtem U, Sirnes PA, Allmen RS, Vrints CJ; ESC Committee for Practice Guidelines.. 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 Nov 1;35(41):2873-926.

[xvi] Hiratzka LF, Bakris GL, Beckman JA, Bersin RM, Carr VF, Casey DE Jr, Eagle KA, Hermann LK, Isselbacher EM, Kazerooni EA, Kouchoukos NT, Lytle BW, Milewicz DM, Reich DL, Sen S, Shinn JA, Svensson LG, Williams DM; American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.; American Association for Thoracic Surgery.; American College of Radiology.; American Stroke Association.; Society of Cardiovascular Anesthesiologists.; Society for Cardiovascular Angiography and Interventions.; Society of Interventional Radiology.; Society of Thoracic Surgeons.; Society for  Vascular Medicine.. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with Thoracic Aortic Disease: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American Association for Thoracic  Surgery, American College of Radiology, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine. Circulation. 2010 Apr 6;121(13):e266-369.

[xvii] Brunkwall J, Kasprzak P, Verhoeven E, et al. Endovascular repair of acute uncomplicated aortic type B dissection promotes aortic remodeling [correction appears in Eur J Vasc Endovasc Surg. 2015;50(1):130]. Eur J Vasc Endovasc Surg. 2014;48 (3):285-291.

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Emergency Medicine Resident

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