Aortic Dissection

Overview

Epidemiology

• 5–30 cases per 1 million people per year
• More common in men than women (3:1)
• More common in African Americans than Caucasians
• Peak incidence at age 50–65 years

Etiology

• Hypertension (70% of dissection patients)
• Atherosclerosis
• Connective tissue disorders
  • Marfan syndrome
  • Ehlers-Danlos syndrome
  • Loeys-Dietz syndrome
  • Cystic medial necrosis 
• Vasculitis
  • Giant cell arteritis
  • Takayasu arteritis
  • Behcet’s disease
• Anatomic abnormalities
  • Bicuspid aortic valve
  • Coarctation of aorta
• Trauma involving rapid deceleration
• Iatrogenic
  • Prior cardiac or aortic surgery
  • Cardiac catheterization
• Drugs 
  • Amphetamines
  • Cocaine

Classification

• Stanford classification:
  • Type A: involvement of the ascending aorta
  • Type B: involvement of the descending aorta (distal to the origin of the left subclavian artery)
• DeBakey classification:
  • Type I: Dissection originates in the ascending aorta and involves the descending aorta.
  • Type II: Dissection involves only the ascending aorta.
  • Type III: Dissection involves only the descending aorta (distal to the subclavian artery).
    • Type IIIa: ends above the diaphragm
    • Type IIIb: extends below the diaphragm

Pathophysiology

• The aorta is more likely to rupture than any other vessel in the body.
  • 90% of dissections occur within 10 cm of the aortic valve.
  • 2nd-most common location is just distal to the take-off of the left subclavian.
• Contributing factors to aortic injury: 
  • Continuously high pulsatile pressure and shear stress
  • Connective tissue disorders are characterized by cystic medial necrosis.
    • Degenerative changes in collagen, elastin, and smooth muscle 
    • Weakens the wall of the aorta
• Intimal tear develops → blood flows into the media → formation of a false lumen
  • True lumen
    • Lined by intima
    • Typically the smaller lumen
  • False lumen
    • Within the media
    • Larger lumen, slower flow, and elevated mean pressures
    • Elevated pressures can cause compression of the true lumen.
• Dissections can extend proximally and/or distally for variable distances.
  • Antegrade toward the iliac bifurcation
  • Retrograde toward the aortic root and heart
• Consequences:
  • Compromised blood supply to arterial branches off the aorta
    • Ischemic stroke
    • Spinal cord ischemia
    • Mesenteric ischemia
    • Renal ischemia
  • If the dissection spreads through the adventitia, there is a significant risk for aortic rupture.
    • Increased risk in ascending aortic dissections
    • Leads to hemorrhagic shock and death
  • Compression symptoms from an enlarged false lumen
  • Ascending aortic dissections:
    • Hemopericardium → cardiac tamponade 
    • Occlusion of the coronary sinus → coronary ischemia
    • Severe aortic regurgitation (AR) → heart failure
  • Descending aortic dissections: extension into the iliac arteries → claudication and limb ischemia
• Other mechanisms of dissection:
  • Rupture of vasa vasorum → intramural hematoma → may rupture the overlying intima
  • Penetrating aortic ulcer from atherosclerotic disease

Clinical Presentation

Symptoms

• Sudden-onset, severe, tearing chest pain (90% of patients)
  • Anterior chest pain (Stanford type A)
  • Back pain between the shoulder blades (Stanford type B) 
  • Radiation to the neck or jaw, particularly if dissection extends into the branches of the aortic arch
• Painless dissection occurs in 10% of individuals, most commonly those with connective tissue disorder.
• Neurologic symptoms:
  • Syncope
  • Altered mental status
  • Stroke
  • Hemiplegia/hemiparesis
  • Hemianesthesia 
• Compression symptoms:
  • Dysphagia (esophageal compression)
  • Hoarseness (left recurrent laryngeal nerve compression)
  • Horner’s syndrome (superior cervical sympathetic ganglion compression)
    • Ptosis
    • Myosis
    • Anhidrosis

Physical exam

• Cardiovascular:
  • Hypertension due to: 
    • Baseline essential hypertension
    • ↑ In circulating catecholamines
  • Hypotension 
    • Poor prognostic sign
    • May be due to cardiac tamponade, severe AR, or aortic rupture
  • > 20-point difference in blood pressure between arms
  • Asymmetric pulses (pulse deficit)
  • Tachycardia
  • AR murmur
    • Auscultated to the left of the sternal border
    • Soft, high-pitched, early diastolic decrescendo 
    • Wide pulse pressure
  • Evidence of cardiac tamponade:
    • Pulsus paradoxus
    • Jugular venous distension
    • Muffled heart sounds
• Musculoskeletal:
  • Acute limb ischemia
    • ↓ Or absent peripheral pulses
    • Pallor
    • Pain
    • Paresthesia
    • Poikilothermia
    • Motor deficit

Diagnosis

Initial imaging

• Chest X-ray may show: 
  • Widened mediastinum
  • Obliteration of the aortic knob
  • Double aortic contour
  • Inward displacement of calcification
• Electrocardiogram (ECG) to evaluate for signs of myocardial infarction

Laboratory workup

• D-dimer
  • Negative values can be used to rule out dissection.
  • Elevated values are nonspecific.
• Complete blood count
  • Anemia → poor prognosis, possible rupture
  • Leukocytosis → stress state  
• Basic metabolic panel
  • ↑ Creatinine → renal artery ischemia or prerenal azotemia
• ↑ Troponin → coronary artery involvement and myocardial ischemia
• ↑ Lactic acid → poor perfusion
• Type and screen → if blood products are needed
• Prothrombin time and partial prothromboplastin time → evaluate for coagulopathy

Definitive diagnosis

• CT angiogram of the chest, abdomen, and pelvis
  • Used in stable patients
  • Use caution if the patient has abnormal renal function.
  • Findings: true and false lumen, intimal flap, intraluminal thrombus
• Transesophageal echocardiography (TEE)
  • Can be considered in unstable patients to identify cardiac tamponade
  • Greater sensitivity and specificity than TTE
  • Most useful for ascending aortic dissection
  • Findings: false lumen, coronary involvement, aortic valve regurgitation, pericardial effusion
• Magnetic resonance angiography (MRA): an alternative to CT angiogram

Management

Acute management

• 2 large-bore intravenous (IV) lines
• Cardiac and arterial blood pressure monitoring
• Supplemental oxygen
• Analgesia
• Anti-impulse therapy (minimize shear stress):
  • Target systolic blood pressure < 120 mm Hg 
  • Target heart rate < 60/min
  • 1st line: IV beta-blockers (esmolol, labetalol) to prevent reflex tachycardia
  • Alternatives: IV nitroprusside or calcium channel blockers 
• For hypotension:
  • IV fluid resuscitation
  • Blood transfusions 
  • Vasopressors

Type A dissections

Type A dissections require emergent surgical intervention for replacement of the involved ascending aorta or the entire ascending aorta with Dacron graft.

Type B dissections

• Can be managed with anti-impulse therapy
• May require surgical intervention with open versus endovascular repair for the following scenarios:
  • Rupture
  • Intractable pain
  • Aneurysmal dilation > 5 cm
  • End-organ malperfusion or limb ischemia
  • Retrograde dissection into the ascending aorta

Long-term management

• Oral antihypertensive therapy (lifelong)
• Avoid strenuous physical activity.
• Young patients may be screened for genetic conditions.
• Serial follow-up imaging to monitor for:
  • Dissection extension or recurrence
  • Aneurysm formation
  • Surgical anastamotic leakage

Differential Diagnosis

• Myocardial infarction: ischemia of the myocardium due to partial or complete obstruction of the coronary arteries. Most often due to atherosclerosis of the coronary arteries. Presentation can mimic a dissection, with acute-onset chest pain. However, the pain does not typically radiate to the back and gradually increases in severity, and is usually accompanied by elevated troponins, typical ischemic ECG changes (ST elevations or depressions), and wall motion abnormalities on transthoracic echo.
• Horner’s syndrome: interruption to the sympathetic chain innervating the eye due to compression, lesion of the neuron, or stroke. Characterized by a constricted pupil (miosis), drooping of the upper eyelid (ptosis), and absence of sweating of the face (anhidrosis). A chest X-ray should be ordered to evaluate for an apical lung mass.
• Aortic regurgitation: insufficiency of the aortic valve, causing the backflow of blood into the left ventricle following systole when the valve is closed. Characterized by soft, high-pitched, early diastolic, decrescendo murmur heard best at the 3rd intercostal space left of the sternal border. Transthoracic echocardiography is used to confirm the diagnosis.
• Pericardial effusion and tamponade: fluid in the pericardial sac, which can cause compression of the heart and lead to tamponade physiology. Tamponade physiology prevents the heart from filling, resulting in hemodynamic collapse. Beck’s triad of distended neck veins, hypotension, and muffled heart sounds is often seen on physical exam. Diagnosis is confirmed with transthoracic echocardiography, and management involves drainage of the pericardium.
• Pneumothorax: a life-threatening condition in which air collects in the pleural space, causing partial or full collapse of the lung. Pneumothorax can be traumatic or spontaneous. Patients present with a sudden onset of sharp chest pain, dyspnea, and diminished breath sounds on exam. A large or tension pneumothorax can result in cardiopulmonary collapse. Diagnosis is made with imaging. Management includes needle decompression and chest tube (thoracostomy) placement.
• Pulmonary embolism: obstruction of the pulmonary arteries, most often due to thrombus migration from the deep venous system. Signs and symptoms include pleuritic chest pain, dyspnea, tachypnea, and tachycardia. Severe cases can result in hemodynamic instability or cardiopulmonary arrest. A chest CT with angiography is the primary method of diagnosis. Management includes oxygenation, anticoagulation, and thrombolytic therapy for unstable patients.