Acute Aortic Dissection
- Oct 31st, 2014
- Jennifer Robertson
Jennifer Robertson, MD
Attending Physician – EM, Cleveland Clinic
Edited by Alex Koyfman, MD
Aortic dissection is a life-threatening yet infrequent diagnosis, estimated at about three cases in every 100,000 person years (1,2). Because of its low frequency and emergency nature, large randomized controlled trials are difficult to conduct (3). Thus, the International Registry of Acute Aortic Dissection (IRAD) was established in 1996 to obtain up-to-date data on patients with acute aortic dissection. Currently, 30 large referral centers in 11 countries participate. Most novel research on aortic dissection is based on IRAD data.
Aortic dissection is defined as disruption of the layers of the aorta. On occasion, the dissection may originate from a penetrating atherosclerotic ulcer or from an intramural hematoma (4,5). However in 90% of patients, dissection occurs from a primary tear in the intima (4). Blood then travels through the media, resulting in separation of the layers and a false lumen. Under high blood pressure, the dissection can then propagate along the entire length of the aorta (4,6) and hypoperfusion can occur, usually by obstruction of the true lumen (6,7).
Although not present in most patients with dissection, aneurysm is a known risk factor (4). Other risk factors include family history of aneurysm, hypertension, old age, atherosclerosis, Marfan Syndrome, Turner Syndrome, Ehlers-Danlos syndrome, bicuspid aortic valve, and history of aneurysmal or dissection repair (4,6,8,9,10). Cocaine use and even heavy weight lifting are also risk factors (4).
By definition, the diagnosis of acute aortic dissection is made within 2 weeks after initial symptoms while chronic aortic dissection is made after 2 weeks (6). Generally, dissections are classified by their location. Two well-known classification schemes include the Stanford and DeBakey systems. In the Stanford classification, type A includes the ascending aorta and type B does not. The DeBakey classification includes types 1 through 3 with type 1 involving the entire aorta, type 2 involving the ascending aorta and type 3 involving the descending aorta. Classification is important as it helps determine surgical or medical management (4).
The diagnosis of aortic dissection requires a high level of suspicion (4). Symptoms of dissection may be similar to other conditions such as acute coronary syndrome, pleurisy, and even stroke (6). The diagnosis should be considered in any patient with syncope, chest pain, back pain, abdominal pain, and/or unexplained neurologic deficits (4).
Pain is the most common symptom and 90% of patients present with back and/or chest pain (4). The pain is typically described as sharp, ripping, or tearing and can migrate as the dissection progresses. In a 2002 review article by Klompas, 274 articles were identified to evaluate for signs and symptoms of acute aortic dissection (11). The sensitivity of any pain was 90% while pain of sudden onset had 84% sensitivity. A pulse deficit, as well as focal neurologic deficits, was also supportive of the diagnosis (11). “Painless” dissection can also occur but is rarer and occurs in patients with heart failure, syncope, or neurologic symptoms (4). Heart failure is related to severe aortic regurgitation and syncope may occur due to aortic rupture or hemopericardium with cardiac tamponade (12). Vascular compromise can occur in any junctional vessel causing syndromes such as acute myocardial infarction, paraplegia, mesenteric ischemia, and limb ischemia (6).
Physical exam can also vary. Most patients with type B dissection are hypertensive upon presentation, while many with type A dissections are normotensive. (6). Based on IRAD data of 591 patients with type A dissection, 32% were hypertensive, 45% normotensive and 14% hypotensive (13). On the other hand, of 384 patients with type B dissection, 69% were hypertensive and only 3% were hypotensive (9). Interestingly, in both type A and type B dissections, pulse deficits were found to be uncommon and only found to be present in about one quarter of patients (9,13). An adequate vascular exam is still necessary, however, and should be done on all patients with suspected aortic dissection (4).
Any suspicion of aortic dissection should prompt clinicians to initiate work-up immediately. An initial chest x-ray may provide some clues as it may show abnormal aortic contour, pleural effusion, intimal calcification, or wide mediastinum. However, it is important to note that chest x-rays are normal in 12 to 15% of patients with dissection (4). Thus, a negative x-ray does not exclude dissection. Additionally, electrocardiography (EKG) is also usually normal or non-specific (6). However, per current American Heart Association (AHA) and American College of Cardiology Foundation (ACCF) guidelines, an EKG should always be obtained as myocardial infarction is more common than dissection and any EKG abnormalities should be treated as a primary cardiac event 4).
Overall, the presentation of thoracic aortic dissection is inconsistent, and cannot be ruled out based on medical history, examination, EKG, or plain radiography findings. Thus, if aortic dissection is suspected at all, clinicians should initiate more definitive testing such as computed tomographic (CT) imaging, magnetic resonance imaging, or transesophageal echocardiography (TEE) (4,6). All three imaging studies have high sensitivity and specificity in diagnosing aortic dissection (4,14).
The death rate in acute dissection is as high as 1% per hour in the first 24 hours (4,15). Treatment must, thus, be immediately initiated. Early management includes controlling blood pressure and heart rate, which decreases aortic wall pressure. Intravenous beta blockers such as esmolol, metoprolol or labetalol, should be initiated and titrated to a heart rate less than 60 bpm and a systolic blood pressure of 100 to 120 mmHg (4,6,16). If patients have contraindications to beta blockade, non-dihydropyridine calcium channel blockers may be used instead (4). Beta blockers should also be used cautiously in acute aortic regurgitation. If systolic blood pressure remains greater than 120 mmHg after adequate beta blockade or rate control, then vasodilators should be administered (4). Agents such as nicardipine, nitroglycerin and sodium nitroprusside may be used (4,16). If vasodilators are used, it is important to note that they should never be given prior to beta blockade as this can lead to reflex tachycardia and greater aortic wall stress.
If the patient is hypotensive, medical management is limited, as surgery is really what is required (4). One should always immediately administer fluids. Although vasopressors can be added to maintain adequate perfusion, they can increase aortic stress and worsen the clinical picture. Per the AHA/ACCF, any hypotension or shock in acute dissection really suggests need for immediate operative management (4).
All patients should be transferred to tertiary care centers where staff is experienced in managing aortic dissections. Type A dissections should be evaluated more urgently for surgical repair as immediate life threatening complications such as rupture can occur. Per AHA guidelines, type b dissections can be managed medically unless life threatening complications such as hypoperfusion, enlarging aneurysm or progress occur (4). Regardless of location, however, the AHA does recommend surgical consultation for all aortic dissections, regardless of location (4).
Although not new, one topic that remains a source of debate is the use of D-dimer and its role in the diagnosis, namely the rule out of, aortic dissection (please go here for extended discussion: http://www.emdocs.net/d-dimer-in-aortic-dissection-workup/). While many studies have shown a high sensitivity of D-dimer in ruling out dissection, especially in the first 24 hours, (9,17,18), others have shown conflicting data (19,20,21). In order to rule out an aortic dissection with a negative d-dimer, the pre-test probability has to be very low. D-dimer may be useful to rule out the diagnosis in low-risk patients (18) but currently, there are no validated scoring systems, such as the Well’s score for pulmonary embolism, that can determine patients’ pre-test probability (4,22,23). However, in 2010, the AHA/ACCF did publish a risk scoring system called the aortic dissection risk score (ADD) that divides patients into low, intermediate, and high risk of aortic dissection (4). The full algorithm can be viewed in the article by Hiratzka et al, but essentially it helps clinicians risk-stratify patients. Recent research has found this risk score to be highly sensitive (95%) for detecting aortic dissection (24).
Most recently, other studies have evaluated the aortic dissection detection (ADD) risk score and its combined use with d-dimer for ruling out aortic dissection. Nazerian et al published data in 2014 that evaluated the ADD risk score plus D-dimer to help rule out aortic dissection. They found that D-dimer < 500 had a sensitivity of 100% with an ADD risk score of zero and had a sensitivity of 98.7% in those patients with an ADD risk score of less than 1 (25). Nazerian et al also published comparable data in a study that was published in 2013 (26). Similarly, in 2014, Baez et al found that the combined use of the ADD and D-dimer may provide useful diagnostic information that may rule out aortic dissection (27). More studies need to be conducted, however these studies may provide a start to finding data that will help emergency physicians quickly rule out aortic dissection without radiation or invasive, costly studies. At this time, the AHA/ACCF guidelines do not recommend the use of D-dimer in ruling out dissection (4). Thus, emergency physicians should continue to have a high level of suspicion and image thoughtfully until further studies can be conducted on risk scoring and the use of D-dimer.
Bottom Line/Pearls & Pitfalls
- Aortic Dissection remains a difficult diagnosis
- Emergency Physicians should keep a high clinical suspicion
- Heart rate / blood pressure control and surgical referral is essential in management
- The AAD risk score is still being tested but may be useful with D-dimer in ruling out low-risk patients
- Emergency physicians should continue to image any patient with concerning symptoms and exam finding
Hiratzka LF, Bakris GL, Beckman JA, et al. 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;121:e266-e369.
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