dissecting aortic aneurysm; aortic dissection (acute aortic syndrome)

Introduction

Includes acute aortic syndromes:

• acute aortic dissection
• aortic intramural hematoma
• penetrating atherosclerotic ulcer

Classification

• proximal (type A): those that involve the ascending aorta
• distal (type B):
  • involvement limited to the descending aorta*
  • origin distal to the left suclavian artery
• acute: < 2 weeks
• chronic: > 2 weeks

* rarely isolated to the infrarenal aorta

Etiology

• cystic medial necrosis
• hormonal state of pregnancy predisposes to dissection during labor
• congenital disorders
  • Marfan's syndrome
  • Ehlers-Danlos syndrome
  • Turner's syndrome
  • coarctation of the aorta
• hypertension
• trauma including iatrogenic trauma
• inflammatory conditions
  • polychondritis
  • temporal arteritis
• cocaine increases risk

Epidemiology

• may occur at any age
• mean age is 59 years
• male/female ratio is 3/1

Pathology

• intimal tear
  • primary
  • secondary to cystic medial necrosis with intramural hemorrhage
  • penetration of blood from the lumen into the media with separation of the intimal & adventitial aortic layers
• spontaneous aortic intramural hematoma
  • formation within the vessel wall from diseased vaso vasorum
  • splits aorta into 2 layers creating a false lumen
  • no intimal tear
• penetrating aortic ulcer
  • gradual erosion of the internal elastic lamina by an expanding atheromatous plaque
  • occurs in descending thoracic aorta
  • generally does NOT propagate longitudinally
• propagation may occur in the anterograde or retrograde direction (exception is penetrating aortic ulcer)
• a secondary intimal tear may occur at the aortic/iliac bifurcation to produce a double-barrel aorta

Clinical manifestations

• pain is the predominant symptom
  • sudden, sharp, crushing substernal &/or back pain
    • chest pain, abdominal pain &/or back pain
  • may be described as ripping or tearing pain
  • often migrates to the neck, jaw, flanks or legs
  • onset is so catastrophic that patients may stagger or fall to the ground
  • if onset is gradual, pain may be absent
• generally blood pressure is maintained in contrast to MI
  • hypertension at presentation is more common than hypotension
  • patients with proximal dissection may present with hypotension; consider
    • pericardial tamponade
    • aortic rupture
  • if subclavian artery is involved, blood pressure measurements in affected arm may be low
• loss of peripheral pulse
  • common with proximal dissection (50%)
    • may occur if subclavian artery is involved
  • uncommon with distal dissection
• neurologic manifestations are more common with proximal than distal aortic dissection (36% vs 6%)
  • mental status changes may occur secondary to impaired cerebral perfusion or administration of narcotics for pain control
  • syncope may occur secondary to pain or hypotension or may be the presenting symptom
  • hemiplegia or paraplegia may be present
  • peripheral ischemic neuropathy
• dyspnea is generally present, but rarely the presenting symptom
• aortic insufficiency
  • occurs in 2/3 of patients with proximal dissection
  • generally the cause of heart failure in patients with aortic dissection
  • diastolic murmur
  • elevated central venous pressure may be observed from right heart failure as a consequence of left heart failure
• pericardial friction rub (rare) is often followed by pericardial tamponade
  • pulsus paradoxus
• tracheal tug due to traction on the left main bronchus during systolic expansion of dissected aorta (rare)
• clinical examination insufficiently sensitive to rule out aortic dissection

Laboratory

• D-dimer within first 24 hours is useful for ruling out aortic dissection
  • with cutoff of 500 ng/mL:
    • negative likelihood ratio = 0.07
    • positive likelihood ratio = 1.82

Diagnostic procedures

• electrocardiogram:
• sinus tachycardia
• low voltage (LVH)
• ST segment depression is most mommon ECG abnormality
• generally does NOT show evidence of myocardial ischemia unless dissection occludes a coronary artery
  • ST segment dep

Radiology

• chest X-ray may show widening of aorta
  • widened mediastinum especially with ascending aortic dissection
  • calcific plaques on intima may be widely separated from outer border of aorta
• CT angiography diagnostic test of choice
  • high sensitivity & specificity
  • FAST
• CT or MRI of thorax*
  • useful for chronic aortic dissection in stable patients
  • a dark band seen bisecting the aorta into two unequal parts (CT image)
    • a dissection flap in the aorta is seen in another view (CT image)
• transesophageal echocardiogram (TEE)*
  • visualization of true & false lumens based on presence or absence of blood flow
  • intimal flap
  • associated aortic insufficiency
  • involvement of proximal coronary arteries
• aortic angiography
  • previously gold standard
  • extent of dissection
  • degree of branch vessel involvement including coronary arteries
  • associated aortic regurgitation

* CT, MRI & TEE with equally reliable diagnostic value

Complications

• proximal progression of dissection
  • distortion aortic valve to cause aortic regurgitation
  • occlusion of coronary ostia resulting in MI
  • hemopericardium
    • pericardial friction rub
    • cardiac tamponade
  • swelling at the base of the aorta
    • pulsating sternoclavicular joint
• distal progression of dissection
  • occlusion of arterial branches
    • carotid artery
    • vertebral arteries
    • renal arteries
    • others
  • loss of arterial pulses
  • focal neurologic deficits
  • patency of false lumen & maximum aortic diameter > 4 cm is associated with greater risk of progression to organ damage from perfusion insufficiency, aortic rupture & death
• late aneurysm formation
  • region of dissection
  • aortic site remote from dissection
  • cause of mortality in up to 30% of patients
• thromboembolism: stroke, myocardial infarction
• cardiac tamponade
• hemothorax

Differential diagnosis

• myocardial infarction
  • 1-2% of proximal aortic dissections extend to proximal coronary arteries & cause MI
  • an ECG consistent with myocardial ischemia or infarction does not rule out concurrent aortic dissection
• aortic insufficiency without aortic dissection
• non-dissected aortic aneurysm
• pericarditis
• musculoskeletal chest pain
• mediastinal tumors
• pulmonary embolism
• esophageal disorders
• pleurisy

Management

• pharmacologic therapy
  • administration of thrombolytic agents is CONTRAINDICATED with aortic dissection
  • beta blocker prior to vasodilator
    • target pulse rate < 65/min
    • systolic blood pressure < 120 mm Hg in 1st hour
    • propranolol: 5 mg IV push, then 1 mg IV every 5 min up to 10 mg
    • labetalol: 5-10 mg IV every 2 min, then 40-120 mg/hour
    • metoprolol: 5 mg IV every 2 min up to 15 mg, then 50 mg PO every 6 hours
    • esmolol: 30 mg IV bolus, then 3-12 mg IV
    • verapamil or diltiazem if beta-blocker is contraindicated
  • vasodilators
    • nitroprusside (must use with beta-blocker)
      • begin 25 ug/min IV until systolic BP is 100-120 mm Hg
      • 20-800 ug/min IV
    • nifedipine (sustained-release)
      • 10 mg PO, then 10-40 mg PO every 8 hours
    • enalaprilat
      • 0.625 mg IV, then 0.625-5.0 mg IV every 6 hours
      • MKSAP19 nixes enalaprilat
    • do not use hydralazine; increases shear stress
  • analgesia - morphine sulfate 3-5 mg IV every 10 min PRN to reduce systolic shear forces
• surgery
  • emergent surgery for proximal aortic dissection (type A)* or proximal aortic intramural hematoma
    • open surgical repair is standard of care (2022)
    • resection of the most severely damaged aortic segment
    • decompression of the false channel
    • resuspension or replacement of the aortic valve may be indicated
  • patients with distal aortic dissection (type B)
    • indications for emergent surgery
      • Marfan's syndrome
      • occlusion of a major aortic branch with visceral or limb ischemia
      • renal arteries involved*
      • progressive dilation or extension despite appropriate medical therapy
      • persistent pain
      • persistent severe hypertension
      • contained (aortic enlargement) or threatened aortic rupture
      • penetrating atherosclerotic ulcers > 20 mm in diameter & > 10 mm in depth
      • penetrating atherosclerotic ulcers associated with hematoma
      • uncontrolled pain
    • fenestration of dissecting membrane may be an option for emergent surgery
    • otherwise, elective surgery is an option
      • percutaneous placement of endovascular stent(s)
    • may be treated medically if no complications
  • uncomplicated penetrating aortic ulcer may be treated medically
• follow-up
  • continued risk of re-dissection
  • long blood pressure control even after surgical correction
    • beta blockers
    • verapamil
  • chest X-ray & non-invasive imaging quarterly for 1st year & biannually thereafter

* emergency surgery also indicated for Type A intramural hematoma

* type B aortic dissection extending through the level of the of the origins of the renal arteries are not necessarily canditates for urgent surgery

More general terms

• aortic aneurysm
• dissecting aneurysm

Patient information

aortic dissection patient information