Acute Aortic Syndromes

Background

Acute aortic dissection is part of a spectrum of diseases referred to as Acute Aortic Syndromes which basically encompasses 3 related conditions: 

(1) Aortic dissection
(2) Intramural hematoma (lacks blood flow in the false lumen or its lack of an intimal flap or entry point. Believed to originate from a rupture of the vasa vasorum within the medial layer; or from microscopic intimal tears )
(3) Penetrating atherosclerotic ulcer (typically seen in older population and often found incidentally, may progress to intramural hematoma)

The pathology, diagnosis, and treatment of these three entities are similar

Presentation
While aortic dissection usually presents with severe pain, its presentation can be more subtle and should be considered in anyone with chest pain, back pain or abdominal pain and pain with either syncope or focal neurological deficits.  Aortic dissection can also present as an acute stroke. There are 2 main anatomic classification systems: 

Stanford type B dissections are further classified as:
1. Complicated - Radiographic evidence of thoracic aortic rupture (eg, blood outside the aortic wall); ischemia involving the viscera, kidneys, spinal cord, or lower extremities; persistent pain; or rapid expansion in the distal arch or proximal descending aorta to a total aortic diameter of > 4.5 cm. These findings require immediate intervention due to the threat to life and limb.
2. Uncomplicated


The dissection creates a new false lumen, which separates the media from the adventitia and can extend either anterograde or retrograde involving the aortic root, arch, or any of the main aortic branches. The false lumen may compress the true lumen and compromise blood flow to distal arteries and causing ischemic complications such as renal failure, stroke, spinal infarction, limb ischemia, and myocardial events.

Classically, aortic dissection will present with abrupt chest or back pain, but about  5% of patients with an acute aortic dissection will have no pain. 

Aortic dissection should always be considered in the differential diagnosis of patients with suspected acute coronary syndromes or pulmonary embolism. 

Atypical presentations can also occur. 

• Syncope has been reported in up to about 20% of patients
• Acute neurological deficits or coma occur in 30% of patients presenting with an acute type A dissection. Neurological findings can be associated with aortic dissections secondary to the extension of the dissection into the aortic branches. These branches can be occluded by either expansion of the false lumen occluding the true lumen or by emboli from an expanding thrombus. Deficits may occur from insults to the brain or spinal cord.

• Patients may be hypertensive (49%), normo- tensive (35%) orhypotensive (8%), or in shock (8%). The presence of hypotension or shock is an ominous finding. 
• Blood pressure discrepancy can occur when a dissection extends into a branch of the aorta occluding the subclavian artery. A difference of 20 mm Hg between arms is considered positive and can be suggestive of an aortic dissection (this finding cannot be used to rule out dissection); however, 20% of the population will have a blood pressure differential without an aortic dissection.
• A pulse deficit is defined as having weak or no pulse on the affected side. However, data from the IRAD database of 2538 patients founda pulse de cit or blood pressure differential in only 20% of patients.
• An aortic dissection may extend retrograde and involve the aortic valve or coronary arteries. A diastolic murmur can be heard in about 1/3rd of patients with an aortic dissection and may represent severe aortic regurgitation but the presence of a diastolic murmur is neither sensi- tive nor specific for aortic dissection.
• 2-5% of patients with aortic dissections will have concurrent myocardial ischemia. Proximal aortic dissections can dissect into the right coronary artery, causing occlusion, and can present with a STEMI. If clinical suspicion for aortic dissection is present, other diagnostic modalities should be used to evaluate for proximal aortic dissection prior to anticoagulation or thrombolytics. 

Risk Factors

• Poorly controlled hypertension
• Connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome)
• Congenital valvular disorders (eg, bicuspid aortic valve)
• Aortic coarctation
• Homocystinuria
• Previous cardiac surgery
• Familial aortic dissections, aortic aneurysms
• Pheochromocytoma
• inflammatory vasculitis
• Sympathomimetics (eg, cocaine)
• Cardiac surgery (eg, aortic valve replacement, coronary artery bypass grafting) or percutaneous catheter placement (eg, cardiac catheterisation),

Diagnosis

D-Dimer
More and more evidence is accumulating in support of the use of D-dimer as a screening tool for aortic dissection but currently, only a few small studies have looked at the sensitivity of D-dimer in ruling out aortic dissection (need further validation). Also, Intramural hematoma or aortic dissections with a thrombosed false lumen can have a false negative D-dimer. If there is sufficient clinical suspicion for an acute aortic dissection, advanced imaging is indicated. 

A Negative D-dimer cannot rule out Aortic Dissection

Imaging Modalities for Acute Aortic Syndrome

CXR
Chest radiography can suggest an aortic dissection. Abnormalities are seen in approxi- lately about 88% of patients. A widened mediastinum is commonly associated with aortic dissection and is seen in approximately 60% of patients. 

A normal CXR cannot rule out an aortic dissection.

Treatment

• ABCs
• Adequate Pain Relief (Morphine or Fentanyl)
• Target HR< 60 beats/min and Target SBP  between 100-120 mm Hg. Always start with Beta Blockers first (not vasodilators)
• In case of cocaine toxicity, use benzodiazepines to decrease the sympathetic drive.
• Type and Screen
• If hypotensive with poor perfusion then use inotropes (can potentially worsen dissection due to increase in shearing forces) or consider pericardicentesis in cases of tamponade (poor prognosis)

• Emergent Vascular Surgery Consultation - Type A acute aortic dissections require prompt surgical treatment. Definitive treatment of type B acute aortic dissections is unclear. Uncomplicated distal dissections have traditionally been treated with blood pressure control. Surgery has been reserved for patients who have persistent pain, uncontrolled hypertension, occlusion of a major arterial trunk, frank aortic leaking or rupture, or development of a localized aneurysm. 

Rationale for Beta-Blockers First: Aortic wall stress is directly affected by the velocity of ventricular contraction over time (dP/dt). Initiation of treatment to decrease these shear forces should occur as soon as the diagnosis is made or suspected.intravenous narcotics should also be given and titrated to pain control.  Beta-blocker therapy should be given prior to initiating intravenous vasodilators to prevent reflex tachycardia. However, in cases of severe aortic regurgitation, use of intravenous beta blockers or calcium-channel blockers with caution.  

Chronic Dissection
Patients who present with chronic aortic dissection have already survived their period of greatest mortality risk and are usually treated by blood pressure control and close monitoring unless complications mandate surgery. All patients who have sustained and survived an aortic dissection, regardless of the type of definitive therapy used, require careful long-term surveillance and treatment. 


Documentation:

• Document HPI with pertinent negative findings
• Presence of Absence of risk factors
• Listen for bruits
• Pulsate Mass, BP difference in lies or any pulse deficits
• Neuro Exam and CXR, ECHO findings

Take Home

• Use your gestalt to work up dissections. Read more here on ADvISED Trial.   Currently, no validated clinical decision rule exists to rule out an acute aortic dissection. Historical and physical exam can be used to increase or decrease probability, but atypical presentations are common. 
• Aortic dissection should always be in the differential for patients with chest pain, back pain, or abdominal pain.
  
• Once the diagnosis is made or strongly suspected, ED Management is limited to pain relief, HTN and BP control and urgent Vascular surgery consulnation.
  
• D-dimer and CXR alone should not be used to “rule out” aortic dissection. POCUS can be helpful in unstable patients but it should not be relied upon to rule out an aortic dissection. 
  
  

   References and Further Reading:

1. Friado FJ. Aortic dissection: a 250-year perspective. Tex Heart Inst J. 2011;38(6):694-700. (Review)
2. Hagan PG, Nienaber CA, Isselbacher EM, et al. The Inter- national Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA. 2000;283(7):897-903. (Retrospective; 464 patients)
3. 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 Ameri- can College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American As- sociation for Thoracic Surgery, American College of Radiol- ogy, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Soci- ety of Thoracic Surgeons, and Society for Vascular Medicine. Circulation. 2010;121(13):1544-1579. (Guideline) 
4. Mancini MC. Aortic dissection. Medscape. Available at: http://emedicine.medscape.com/article/2062452-overview.
5. Accessed June 10, 2013. (Review)
6. Hardie AD, Wineman RW, Nandalur KR. The natural his- tory of acute non-traumatic aortic diseases. Emerg Radiol. 2009;16(2):87-95. (Review) 
7. Collins JS, Evangelista A, Nienaber CA, et al. Differences in clinical presentation, management, and outcomes of acute type A aortic dissection in patients with and without previ- ous cardiac surgery. Circulation. 2004;110(11 suppl 1):II237- II242. (Retrospective; 617 patients) 
8. Bossone E, Rampoldi V, Nienaber CA, et al. Usefulness of pulse de cit to predict inhospital complications and mortal- ity in patients with acute type A aortic dissection. Am J Cardiol. 2002;89(7):851-855. (Retrospective; 513 patients) Rogers AM, Hermann LK, Booher AM, et al. Sensitivity of the aortic dissection detection risk score, a novel guideline- based tool for identi cation of acute aortic dissection at initial presentation: results from the international registry of acute aortic dissection. Circulation. 2011;123(20):2213-2218.
9. Lo BM. An evidence-based approach to acute aortic syndromes. Emergency medicine practice. 2013 Dec 1;15(12):1-23.

Posted by:

              

     Lakshay Chanana

     

     Speciality Doctor

     Northwick Park Hospital

     Department of Emergency Medicine

     England

     @EMDidactic