Aortic dissection

An aortic dissection is a tear in the inner layer of the aorta that leads to a progressively growing hematoma in the intima-media space. Risk factors for aortic dissection include age and hypertension. Patients typically present with sudden onset severe pain radiating into the chest, back, or abdomen. A widened mediastinum on chest x-ray is characteristic of the diagnosis. The diagnosis is usually confirmed with CT angiogram in stable patients and transesophageal echocardiography (TEE) in unstable patients. Treatment options range from conservative measures (e.g., blood pressure optimization) to surgery (aortic stent graft), depending on the localization and severity of the dissection. Complete occlusion of branching vessels and aortic rupture are common complications. Even with treatment, mortality rates associated with aortic dissection are high.

• Incidence
  • Peak incidence: 60–80 years of age ^[1]
  • In patients with Marfan syndrome: peak incidence 30–50 years of age) ^[2]
• Sex: ♂ > ♀ ^[1]
• Localization ^[3]
  • Ascending aorta: ∼ 65% of cases
  • Descending aorta, distal to the left subclavian artery: 20% of cases
  • Aortic arch: 10% of cases
  • Abdominal aorta: 5% of cases

Epidemiological data refers to the US, unless otherwise specified.

• Acquired
  • Hypertension (most common risk factor)
    • Approx. 70% of patients with aortic dissection have elevated blood pressure, which can lead to propagation of the dissection and increases the risk of rupture.
    • Exception: In patients < 40 years of age, less than 40% of cases are due to hypertension.
  • Trauma; (e.g., deceleration injury in a motor vehicle accident, or iatrogenic injury during valve replacements or graft surgery)
  • Vasculitis with aortic involvement (e.g., syphilis, Takayasu arteritis)
  • Use of amphetamines and cocaine
  • Third-trimester pregnancy (or early postpartum period)
  • Atherosclerosis
• Congenital
  • Connective tissue disease (Marfan syndrome, Ehlers-Danlos syndrome)
  • Bicuspid aortic valve
  • Coarctation of the aorta

There are two classifications of aortic dissection to help direct management. Stanford classification groups dissections by whether the ascending or descending aorta is involved. DeBakey classification categorizes dissections according to their origin and extent.

Stanford classification ^[4]

• Stanford type A aortic dissection: any dissection involving the ascending aorta (defined as proximal to the brachiocephalic artery), regardless of origin
  • Can extend proximally to the aortic arch and distally to the descending aorta
  • Generally requires surgery
  • Complications include aortic regurgitation and cardiac tamponade.
• Stanford type B aortic dissection: any dissection not involving the ascending aorta
  • Descending aorta; originating distal to the left subclavian artery
  • Most cases can be managed with medical therapy (e.g., beta blockers, vasodilators).

Stanford A = Affects ascending aorta; Stanford B = Begins beyond brachiocephalic vessels

DeBakey classification (rarely used) ^[4]

• Type I
  • Dissections originate in the ascending aorta and continue to at least the aortic arch but typically as far as the descending aorta.
  • Generally requires surgery
• Type II
  • Dissections originate in, and are restricted to, the ascending aorta.
  • Generally requires surgery
• Type III
  • Dissections originate in the descending aorta and most often extend distally.
  • Most cases can be managed by medical therapy.
  • Can be further subdivided into:
    • Type IIIa: limited to the descending thoracic aorta above the level of the diaphragm
    • Type IIIb: extends below the diaphragm

• Common anatomic sites of origin
  • Above (2.2 cm) the aortic root
  • Aortic arch
  • Distal to left subclavian artery
• Transverse tear in the aortic intima (“entry”) → blood enters the media of the aorta and forms a false lumen in the intima-media space → hematoma forms and propagates longitudinally downwards ^[5]
  • Rising pressure within the aortic wall → rupture
  • Occlusion of every single branching vessel (e.g., coronary arteries, arteries supplying the brain, renal arteries, arteries supplying the lower limbs) → ischemia in the affected areas (see “Complications” below)
  • A second intimal tear may result in a “reentry” into the primary aortic lumen.

• Sudden and severe tearing/ripping pain
  • Location
    • Anterior chest (ascending) or back (descending)
    • Interscapular or retrosternal pain
    • Neck and jaw
    • Abdomen or periumbilical, colicky pain
  • Character: migrates as the dissected wall propagates caudally
• Hypertension or hypotension
• Asymmetrical blood pressure and pulse readings between limbs
• Syncope, diaphoresis, confusion or agitation
• A heart murmur (an aortic regurgitation in a proximal dissection)

ECG ^[7]

Should be ordered for all patients. Findings are variable and include:

• Normal findings
• Signs of left ventricular hypertrophy
• Nonspecific changes, such as ST depression and T-wave changes
• ST elevation due to coronary artery occlusion ^[4]

Laboratory studies

• D-dimer: elevated levels ^[8]
• Evaluate for signs of end-organ damage: troponin, BMP, lactate
• Pre-operative labs: CBC, type and screen, BMP, coagulation panel

Imaging

Initial imaging in low to moderate risk patients ^[9][10]

• Chest x-ray (AP view)
  • Characteristic findings
    • May be normal
    • Widened mediastinum (> 8 cm) at the level of the aortic knuckle
    • Alteration of the mediastinal contour seen on serial imaging
    • Mediastinal mass
    • Calcium sign: displacement of the intimal calcification of > 6 mm
  • Additional findings that may be present
    • Double aortic contour
    • Pleural cap
    • Pleural effusion
    • Blurring of the aortic knuckle
    • Tracheal shift
    • Widening of the paratracheal stripe

Normal chest x-ray findings do not rule out aortic dissection. If clinical suspicion for acute aortic dissection persists, perform a second imaging study.

Definitive imaging ^[4]

Definitive imaging is used to determine the type of lumen, location, and extent of the dissecting membrane. The identification of a false lumen is highly suggestive of aortic dissection.

Modalities ^[4]

• CT angiography of the chest, abdomen, and pelvis ^[4]
  • Indications: stable patients, surgical planning
  • Advantages: very high sensitivity and specificity (considered to be the gold standard) ^[4]
  • Suggestive findings
    • Intimal dissection flap
    • Double lumen
    • Aortic dilatation
    • Regions of malperfusion
    • Aortic hematoma (high-attenuation)
    • Contrast leak: indicates rupture

• Magnetic resonance angiography (MRA) of the chest, abdomen, and pelvis
  • Indications: stable patients, contraindications to CTA
  • Advantages:
    • Similar sensitivity and specificity to CTA, without radiation or contrast exposure
    • Can also be used to detect aortic valve pathology and LV dysfunction
  • Disadvantages:
    • Time-consuming
    • Contraindications: renal insufficiency, claustrophobia, metallic implants, pacemakers
    • Not widely available on an emergency basis
  • Suggestive findings: similar to CT angiography
• Transesophageal echocardiography (TEE)
  • Indications:
    • Unstable patients
    • Intraoperative visualization
    • Renal insufficiency or contrast allergy
  • Advantages:
    • Rapid; can be performed at the bedside
    • Quick differentiation between thoracic aortic aneurysm and thoracic aortic dissection
  • Disadvantages: dissection flap can be difficult to distinguish from artifact
  • Findings may include:
    • Dissection flap (with differential Doppler flow)
    • Double lumen in the ascending aorta
    • Thrombosis in false lumen
    • Pericardial effusion
• Other: catheter angiography, ultrasound ^[4]

For other differential diagnosis considerations, see “Differential diagnoses of acute chest pain”.

Acute aortic occlusion ^[11][12]

• Etiology
  • Aortic embolism
    • Referred to as a saddle embolus when located at the aortic bifurcation
    • Commonly caused by cardiac emboli
      • Myocardial infarction
      • Atrial fibrillation
      • Rheumatic heart disease
  • Thrombosis of atherosclerotic aorta
  • Stent or graft occlusion
  • Aortic dissection
• Clinical features: The clinical features of acute aortic occlusion are due to ischemia of the tissues distal to the level of occlusion.
  • Occlusion at aortic bifurcation: bilateral acute limb ischemia (most common presentation)
    • Limb pain
    • Pallor or cyanosis
    • Absent pulse
    • Paresthesia and paralysis
  • Occlusion above aortic bifurcation
    • Bilateral acute limb ischemia
    • Acute abdomen
    • Acute renal failure
• Diagnostics
  • CT angiography (confirmatory test)
  • Investigate the underlying cause
    • ECG
    • Echocardiography
• Treatment
  • Bilateral transfemoral embolectomy
  • Aortobifemoral bypass
  • Thrombolysis

The differential diagnoses listed here are not exhaustive.

Approach ^[4]

• Urgent cardiothoracic surgical consult for all patients with suspected or confirmed dissection, regardless of location. ^[4]
  • Stanford A dissection: immediate surgery.
  • Stanford B dissection: treat conservatively unless complications occur. ^[4][13]
• Blood pressure control is essential in all patients to prevent progression of the dissection
• Supportive care
• Admission to surgical ICU with close monitoring and surveillance imaging

Surgical therapy ^[4]

• Indications
  • All patients with Stanford A dissection ^[4]
  • Patients with Stanford B dissection who develop complications:
    • End-organ damage (ischemia)
    • Hypotension
    • Persistent severe chest pain or hypertension
    • Propagation of dissection
    • Expanding aneurysm
    • Expanding hematoma
    • Rupture
• Procedure
  • Open surgery with the replacement of the dissection with a polyester graft implantation ^[4]
  • Endovascular treatment with aortic stent implantation (only in type B dissections and if the open operative risk is too high) ^[4]

Ascending aortic dissection is a surgical emergency!

Medical therapy

Hypotensive patients ^[4]

• Hemodynamic support: target MAP of 70 mm Hg or euvolemia ^[4]
  • IV fluids
  • Vasopressor support: if the patient remains hypotensive ^[4][14]
    • Norepinephrine
    • Phenylephrine
    • Inotropes should be avoided as they can increase sheer stress on the aortic wall through increased force of ventricular contraction.
• Identify and treat any comorbidities that may be contributing
  • Cardiac tamponade
  • Severe aortic insufficiency
• Expedite operative management.

Avoid inotropes as they can worsen aortic wall stress.

Hypertensive patients ^[4]

• Control hypertension and heart rate: target SBP 100–120 mm Hg and HR ≤ 60 beats per minute ^[4][15]
  • Start with IV beta blocker: to avoid reflex tachycardia
    • Esmolol
    • Labetalol
  • Followed by vasodilator (e.g., IV sodium nitroprusside )^[4]
  • Contraindications to beta blocker: start calcium channel blocker
    • Verapamil
    • Diltiazem
• Patients with dissection of the descending aorta who remain stable on IV treatment can be transitioned to oral medications and discharged with outpatient imaging surveillance.

Start beta-blocker therapy before vasodilators to avoid a reflex tachycardia!

Supportive care

• Patients may require sedation
• Analgesia (e.g., morphine)
• Identify and treat any complications (e.g., mesenteric ischemia, acute kidney injury)

Avoid thrombolytic therapy in patients with suspected aortic dissection.

• Urgent cardiothoracic/vascular surgery consult
• Check ECG
• Check labs
  • D-dimer
  • Pre-operative: type and screen, CBC, coagulation panel, BMP, troponin
• Assess risk and consider definitive imaging (see aortic dissection detection risk score)
• Consider indications for surgical repair (e.g., all type A dissection, type B dissection with complications)
• Blood pressure control: goal MAP 70
  • In hypotensive patients: fluids, vasopressors
  • In hypertensive patients: goal SBP < 120 mm Hg and HR < 60/min
    • Beta blocker (first-line)
    • Sodium nitroprusside if HR is < 60/min but SBP is still > 120 mm Hg after treatment with beta blockers
    • If there are contraindications to beta blockers, use nondihydropyridine calcium channel blockers.
• Supportive care: Pain management
• Continuous telemetry and pulse oximetry
• Frequently monitor blood pressure.
• Monitor urine output.
• Transfer to the ICU or OR.
• Monitor for complications.

• Aortic rupture and acute blood loss: acute back and flank pain (tearing pain); , symptoms of shock → indication for emergency surgery
• Complications of Stanford type A dissections
  • Myocardial infarction (coronary artery occlusion)
  • Aortic regurgitation (extension of the dissection into the aortic valve): new diastolic heart murmur and (exertional) dyspnea
  • Cardiac tamponade combined with cardiogenic shock
  • Pericarditis (slow extension of the dissection into the pericardium)
  • Stroke (extension of the dissection into the carotids)
• Complications of both Stanford type A dissection and Stanford type B dissections
  • Bleeding into the thorax, mediastinum, and abdomen
  • Arterial occlusion followed by ischemia of the:
    • Celiac trunk, superior/inferior mesenteric artery → acute abdomen, ischemic colitis
    • Renal arteries → acute renal failure (oliguria, anuria)
    • Spinal arteries → weakness of lower extremities or acute paraplegia
    • Complete occlusion of the distal aorta → Leriche syndrome (aortoiliac occlusive disease)

We list the most important complications. The selection is not exhaustive.

• In-hospital mortality due to aortic dissection ranges from 9 to 39%, depending on the type of dissection and treatment modality. ^[16][17]

• Blood pressure control
• Smoking cessation ^[4]
• Screening and repair of rapidly expanding aneurysms (see “Therapy” and “Prevention” sections in “Aortic aneurysms”)

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