Aortic Dissection

• Meghana Rao, M.D.
• Philip Stockwell, M.D.

 Basic Information

Definition

Aortic dissection is part of a spectrum of aortic pathologies (acute aortic syndromes) that includes intramural hematomas and penetrating atherosclerotic ulcers. Aortic dissection occurs when blood passes through an intimal tear, separating the intima from the medial layers and creating a false lumen. Intramural hematoma (IMH) occurs when the vasa vasorum ruptures within the medial wall. IMH does not involve an intimal tearing unless a dissection develops. Seventeen percent of IMH will transform into aortic dissection. Penetrating atherosclerotic ulcers, which occur in the setting of extensive aortic atherosclerosis and hypertension, destroy the aortic intima and dissect into the aortic media. Rupture of atherosclerotic plaques with subsequent blood entry into the median wall forms a pseudoaneurysm. Fig. 1 illustrates acute aortic syndromes.

Synonyms

1. Dissecting aortic aneurysm

2. Acute aortic syndrome

3. AAS

ICD-10CM CODES
I71.00	Dissection of unspecified site of aorta
I71.01	Dissection of thoracic aorta
I71.02	Dissection of abdominal aorta
I71.03	Dissection of thoracoabdominal aorta

Epidemiology & Demographics

Incidence

3.5 to 6.0 per 100,000 person-years

Predominant Sex and Age

Males (65%) females (35%), ages 60 to 80 yr; mean, 63 yr

Risk Factors

1. •

   Hypertension (found in up to 77% of patients with aortic dissection)

2. •

   Atherosclerosis (found in up to 31% of patients with aortic dissection)

3. •

   Age (60-80 years)

4. •

   Family history of aortic aneurysms/dissection

5. •

   History of cardiac surgery, aortic valve replacement, intraaortic catheterization

6. •

   Disorders of collagen (Marfan’s syndrome, Ehlers-Danlos syndrome)

7. •

   Vascular inflammation (giant cell arteritis, Takayasu arteritis, rheumatoid arthritis, syphilitic aortitis)

8. •

   Aortic coarctation, bicuspid aortic valve

9. •

   Turner’s syndrome

10. •

    Cocaine abuse (usually within 12 hours of last use of cocaine)

11. •

    Trauma

12. •

    Table 1 summarizes genetically triggered conditions associated with aortic dissection.

    TABLE1 Genetically Triggered Conditions Associated With Aortic DissectionFrom Mann DL, et al.: Braunwald’s heart disease, ed 10, Philadelphia, 2015, Elsevier.

    Marfan syndrome (MFS)	Autosomal dominant disorder of connective tissue caused by FBN1 mutation; incidence of 1 in ≈5000 individuals; multisystem manifestations, including ectopia lentis; mitral valve prolapse, aortic root aneurysm, aortic dissection; skeletal features (pectus deformities, scoliosis, arachnodactyly, hyperflexibility, tall stature, elongated fingers and toes); dural ectasia; spontaneous pneumothorax
    Loeys-Dietz syndrome (LDS)	Autosomal dominant disorder caused by mutations in TGFBR1 and TGFBR2, associated with aneurysms and dissections involving the aorta and branch vessels, often at relatively small diameters and young age; manifestations include craniofacial features (hypertelorism, craniosynostosis, cleft palate, bifid or broad uvula), bluish sclera, arterial tortuosity, velvety and hyperlucent skin, easily visible veins, clubfeet, skeletal abnormalities; phenotypes may vary, including those with more pronounced craniofacial features and those with more cutaneous features; ectopia lentis has not been described in LDS; mutations in TGFB2 lead to a syndrome with an overlap in clinical features of LDS and MFS
    Familial thoracic aortic aneurysm (FTAA) syndromes	Autosomal dominant disorders with variable expression and penetrance leading to TAAs and dissections at variable ages in families; ACTA2 mutations occur in 10-15% of cases of FTAA and are associated with BAV disease, cerebral aneurysms, livedo reticularis, iris flocculi, PDA, moyamoya, and premature coronary artery disease; gene mutations causing familial TAAD include ACTA2, TGFBR1, TGFBR2, FBN1, MYH11, MYLK, TGFB2, SMAD3
    Vascular Ehlers-Danlos syndrome (vEDS)	Autosomal dominant disorder of collagen synthesis caused by a gene mutation in COL3A1 leading to rupture and dissection of the aorta (usually the descending and abdominal aorta) and branch vessels; manifestations include flexible digits, hyperlucent skin with visible veins, varicose veins, typical facial appearance, and spontaneous rupture of the uterus or bowel
    Bicuspid aortic valve (BAV)	Congenital condition affecting ≈1% of the population, familial in ≈9% of cases; often associated with dilation of the ascending aorta and carries increased risk for aortic dissection; gene mutations include NOTCH1 and loci at 15q, 18q, 5q, and 13q; may be associated with FTAA
    Turner syndrome (TS)	Genetic disorder affecting 1 in 2000 live-born girls and caused by complete or partial loss of the second sex chromosome (XO, Xp); women with TS often have BAV and aortic coarctation; associated with ascending aortic dilation for body size and increased risk for aortic dissection, especially when associated with BAV, hypertension, and coarctation
    Aneurysms-osteoarthritis syndrome	Autosomal dominant genetic disorder resulting from mutations in the SMAD3 gene and associated with premature osteoarthritis, osteochondritis dissecans, skeletal features, aortic aneurysms, branch vessel aneurysms, and arterial tortuosity; overlap with LDS phenotype

Classification

Aortic dissection is generally classified according to anatomic location (Fig. 2). Table 2 summarizes classification schemes of acute aortic dissection.

1. •

   Stanford (more commonly used classification system): type A ascending aorta (proximal), type B descending aorta (distal)

2. •

   DeBakey: type I ascending and descending aorta, type II ascending aorta, type III descending aorta

3. •

   Aortic dissection can also be classified by acuity of presentation (acute or chronic), based on the time of onset.

Physical Findings & Clinical Presentation

1. •

   Sudden onset of severe sharp, tearing, or ripping chest pain. However, painless dissection occurs in approximately 6.4% of cases.

2. •

   Anterior chest pain (85% type A, 67% type B).

3. •

   Back pain, abdominal pain (43% type A, 70% type B).

4. •

   Syncope (19% type A, 3% type B), generally secondary to cardiac tamponade or stroke.

5. •

   Congestive heart failure (CHF)

6. •

   May present with hypertension (28% for type A, 66% in type B dissection), although 25% present with hypotension (systolic blood pressure <100 mm Hg), which can indicate bleeding, cardiac tamponade, or severe aortic regurgitation.

7. •

   Pulse and blood pressure differentials (>20 mm Hg between arms) in 19% to 31% of cases caused by partial compression of subclavian arteries.

8. •

   Aortic regurgitation in 18% to 50% of cases of proximal dissection, often with diastolic decrescendo murmur.

9. •

   Myocardial ischemia caused by coronary artery occlusion, most commonly involving the right coronary artery.

10. •

    Stroke in 5% to 10% of patients (secondary to dissection into or decreased blood flow to the carotids).

11. •

    Mesenteric ischemia occurs in 3% to 5% of cases, with external compression, flap prolapse, or involvement of arterial ostia.

12. •

    Horner syndrome (ptosis, miosis, anhidrosis).

13. •

    Vocal cord paralysis or hoarse voice (caused by compression of the left recurrent laryngeal nerve).

Etiology

Genetics, in addition to other risk factors listed previously, contribute to the development of aortic dissection.

Diagnosis

Differential Diagnosis

1. •

   Known as the great imitator: Pulmonary embolism, acute coronary syndrome, aortic stenosis/insufficiency, nondissecting aneurysm, pericarditis, cholecystitis, peptic ulcer disease, pancreatitis, musculoskeletal pain

2. •

   Consider aortic dissection in patients with unexplained stroke, chest pain, syncope, acute-onset CHF, abdominal pain, back pain, and malperfusion of extremities or internal organs. Acute aortic syndromes may be associated with nonspecific signs and symptoms; a high clinical index of suspicion is necessary to detect the disease early in its course.

3. •

   In an emergency situation, a rapid yet comprehensive workup is crucial to reduce diagnostic time delay. This should include clinical assessment, laboratory data (D-dimer and troponin), chest x-ray, electrocardiogram (ECG), and aortic imaging in the appropriate patient.

Laboratory Tests

1. •

   ECG: helpful to rule out MI, although dissection can lead to coronary ischemia

2. •

   D-dimer has a 100% negative predictive value in dissection, but lacks specificity in the setting of acute aortic dissection. However, a negative D-dimer does not rule out intramural hematoma or penetrating aortic ulcer.

3. •

   Three biomarkers with different diagnostic windows can be used in the diagnosis of aortic dissection:

   1. ○

      Smooth muscle myosin heavy chain protein (released from damaged medial smooth muscle) can be used to detect proximal aortic dissections (91% sensitivity and 93% specificity). Myosin heavy chains will peak within 3 hr of dissection and clear within 24 hr of aortic injury.

   2. ○

      CK-BB isoenzyme also peaks within 6 hr of dissection.

   3. ○

      Calponin, a smooth muscle troponin counterpart, increases in aortic dissection with a wider diagnostic window when compared to smooth muscle myosin heavy chain and CK-BB.

   4. ○

      C-reactive protein, fibrinogen, and soluble elastin fragments are under investigation.

Imaging Studies

1. •

   Multidetector CT (Figs. 3 and 4) is considered the gold standard, but its use may be limited in patients with renal failure as it involves the use of IV contrast.

   

   

2. •

   TEE, multidetector CT, and MRI are all highly sensitive (98%-100%) and specific (95%-98%). Test of choice depends on clinical circumstances and hospital availability.

3. •

   Transesophageal echocardiography (TEE) is study of choice in unstable patients with type A dissection but is operator dependent.

4. •

   MRI has high sensitivity and specificity but limited availability; not suitable for unstable patients; contraindicated with pacemakers, metal devices.

5. •

   With medium or high pretest probability, a second diagnostic test should be done if the first is negative.

6. •

   Coronary computed tomographic angiography (CTA) may be an alternative and useful diagnostic study when evaluating for pulmonary embolism, acute coronary syndrome, and aortic dissection.

7. •

   Aortography rarely done, as less sensitive than TEE, CT, or MRI.

8. •

   Chest radiograph may show widened mediastinum (52% in type A dissections and 39% in type B dissections) and displacement of aortic intimal calcium. It is normal in 29% to 36% of patients with aortic dissection.

9. •

   Although the diagnostic sensitivity of transthoracic echocardiography is suboptimal (31% to 55%), it is useful in assessing potential high-risk features or complications, such as pericardial effusion, and making other potential diagnoses. A negative transthoracic echocardiography, however, does not exclude aortic dissection.

Treatment

1. •

   Urgent surgical consultation should be obtained for all thoracic aortic dissection regardless of anatomic location.

2. •

   Proximal dissections (acute type A) require emergent surgery to prevent rupture or pericardial effusion.

3. •

   Distal dissections (Stanford type B) are usually treated medically unless distal organ involvement or impending rupture occurs.

   1. 1.

      Surgical intervention for distal dissections is reserved for patients who have a complicated course, including occlusion of a major aortic branch, propagation of the dissection, enlarging aneurysm, and evidence of aortic rupture.

   2. 2.

      Thoracic endovascular aortic repair (TEVAR) is a less invasive option for complicated type B aortic dissections and is associated with lower short- and midterm mortality than medical therapy.

   3. 3.

      For acute type B dissections, in-hospital mortality in patients managed surgically has been reported to be 33.9% versus those managed with endovascular treatment at 10.6%.

   4. 4.

      Independent predictors of complication and mortality in distal dissections include periaortic hematoma and descending aortic diameter >5.5 cm, partial false lumen thrombosis, primary tear >10 mm, one entry tear, and false lumen >22 mm.

   5. 5.

      There is ongoing debate about a possible beneficial role of TEVAR for uncomplicated type B dissections. Data suggest that 30% of uncomplicated type B dissections will progress to an aneurysm.

Acute General Rx

1. •

   Admit to ICU for monitoring.

2. •

   Target SBP 100 to 120 mm Hg or as low as tolerated; heart rate <60 beats/min to reduce aortic wall stress. Treatment with beta-blockers has been associated with improved survival in all patients with acute aortic dissections.

3. •

   IV beta-blockers are cornerstones of treatment, but multiple medications may be needed.

   1. 1.

      Propranolol 1 mg every 3 to 5 min, metoprolol 5 mg IV every 5 min, or labetalol 20 mg IV, then 20 to 80 mg every 10 min, followed by nitroprusside 0.3 to 10 mcg/kg/min.

   2. 2.

      Vasodilators should not be used without beta-blockade as they can induce reflex sympathetic stimulation and increase aortic shear stress.

   3. 3.

      IV calcium channel blockers with negative inotropy (i.e., verapamil, diltiazem) may be used if beta-blockers are contraindicated.

4. •

   Pain control, often with morphine.

Chronic Rx

1. •

   Chronic aortic dissection (>2 wk) managed with aggressive blood pressure control: target <120/80 mm Hg in most patients.

2. •

   Statin therapy to reduce low-density lipoprotein <70 mg/dl.

3. •

   Tobacco cessation.

4. •

   Minimize strenuous physical activity such as heavy lifting.

5. •

   Serial imaging of the aorta, with multidetector CT or MRI should be performed at presentation, at 1, 3, 6, and 23 months given the higher risk of instability early on, followed by yearly clinical and imaging follow-up.

6. •

   As stated above, endovascular repair should be considered in complicated chronic type B dissections, i.e., when the aortic diameter exceeds 5.5 cm, when there is uncontrolled pain or blood pressure, or when there is rapid growth of the dissecting aneurysm (>4 mm per year).

Disposition

1. •

   90% mortality rate within 2 weeks for an untreated type A dissection.

2. •

   Proximal dissection is a surgical emergency. Time is critical; mortality rate is 1% to 3% per hour, approaching 70% after 48 hours.

3. •

   Overall, in-hospital mortality rate is 22% with proximal dissections (27% treated surgically and 56% treated medically) and 10% to 17% with distal dissections.

4. •

   Table 3 summarizes suggested imaging surveillance of asymptomatic thoracic aortic aneurysms.

   TABLE3 Suggested Imaging Surveillance of Asymptomatic Thoracic Aortic Aneurysms^∗
   (Hiratzka LF, 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 121:e266, 2010.)

   From Mann DL, et al.: Braunwald’s heart disease, ed 10, Philadelphia, 2015, Elsevier.

   Initial Discovery of Aneurysm	Repeated Imaging at 6 Months to Document Stability
   Degenerative aneurysm†
   3.5-4.4 cm	Annual imaging
   4.5-5.4 cm	Annual to biannual imaging
   MFS, BAV with TAA, and familial TAA
   3.5-4.4 cm	Annual imaging
   4.5-5.0 cm	Biannual imaging
   LDS‡
   <4 cm	At least annual imaging
   >4 cm	Biannual imaging

Referral

For ICU management and surgical intervention

Pearls & Considerations

1. •

   Blood pressure control is essential; beta-blocker is first-line medication.

2. •

   Proximal dissection is a surgical emergency.

3. •

   Cardiac tamponade is not uncommon in patients with acute type A aortic dissection. Syncope, altered mental status, and a widened mediastinum on chest radiograph on presentation suggest tamponade, which warrants urgent operative therapy.

4. •

   Surgery for acute type A aortic dissection in patients ≥70 years old can be performed with acceptable outcomes.

Suggested Readings

• R. Erbel, et al.: 2014 ESC Guidelines on the diagnosis and treatment of aortic diseases. Eur Heart J. 35 (41):2873–2926 2014 25173340

• R. Fattori, et al.: Interdisciplinary expert consensus document on management of type B aortic dissection. J Am Coll Cardiol. 61 (16):1661–1678 2013 23500232

• L.A. Pape, 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. 66:350–358 2015 26205591

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