Aortic Dissection

Definition, Etiology, PathogenesisTop

Aortic dissection is caused by a tear of the intima with blood penetrating into the media. This results in the separation of the intima from the media and adventitia and creates a false lumen of the aorta.

Aortic dissections may be divided according to the Stanford classification into type A and type B. Type A aortic dissections refer to dissections involving the ascending aorta, aortic arch, or both regardless of the site of origin (70%). These may extend down into the descending thoracic or thoracoabdominal aorta. Type B aortic dissections occur distal to the left subclavian or even innominate artery and involve the descending thoracic or thoracoabdominal aorta.

The DeBakey classification for aortic dissections is also commonly used. DeBakey type I dissections involve the ascending aorta, arch, and descending thoracic aorta and may extend into the abdominal aorta. DeBakey type II dissections are limited to the ascending aorta. DeBakey type III dissections (like Stanford type B) arise distal to the left subclavian artery.

Risk factors for aortic dissection include hypertension (usually poorly controlled), bicuspid aortic valve and coarctation of the aorta (including patients after surgical correction of these malformations), history of aortic disease (eg, aortic aneurysm) or aortic valve disease, positive family history of aortic disease, congenital connective tissue diseases (Marfan syndrome, Ehlers-Danlos syndrome), cystic medial degeneration (in patients >50 years of age), aortitis, trauma (traffic accidents, iatrogenic), hemodynamic and hormonal factors during pregnancy (50% of aortic dissections in patients aged <40 years occur in pregnant women), Turner syndrome, cardiovascular surgery, professional weightlifting, tobacco smoking, and IV use of cocaine or amphetamines.

Clinical FeaturesTop

Aortic dissection usually manifests as severe chest pain (features: see Table 1 in Chest Pain) that often leads to syncope and does not respond to sublingual or oral nitrates. It may be accompanied by symptoms of shock, neurologic symptoms (cerebral ischemia, less commonly paraplegia, upper or lower limb ischemic neuropathy, Horner syndrome, hoarseness), myocardial infarction (if dissection involves the coronary artery ostia), heart failure (in the case of severe aortic regurgitation) and cardiac tamponade, pleural effusion, acute kidney injury (involvement of the ostia of renal arteries), abdominal pain (involvement of the ostia of the celiac trunk or mesenteric arteries), features of acute limb ischemia, and limb paralysis due to spinal cord ischemia. Physical findings may include high blood pressure (BP) (50% of patients) or hypotension, diastolic murmur audible over the aortic valve caused by severe aortic regurgitation, and pulse deficit in one extremity (in ~30% of patients with dissection of the ascending aorta, aortic arch, or both). The presenting feature may also be syncope without pain and neurologic symptoms.

Symptoms indicative of the severity of the patient’s condition: Very severe pain, tachycardia, tachypnea, hypotension, cyanosis, shock.

DiagnosisTop

Diagnosis should be established immediately (do not prolong diagnostics in a center not capable of providing invasive treatment). Assess the clinical risk of dissection (Table 1). Aortic dissection should be differentiated from other causes of chest pain. Diagnosis must be confirmed with an imaging study (preferably computed tomography angiography [CTA] [Figure 1]; in unstable patients transesophageal echocardiography [TEE] [Figure 2] is equivalent). Chest radiography may reveal enlargement of the cardiac silhouette, rarely of the upper mediastinum; in the case of rupture into the pleural cavity, radiography reveals pleural effusion. Normal results of imaging studies do not exclude aortic dissection. In case of sustained suspicion of aortic dissection despite normal baseline imaging study results, repeated imaging study using CTA or magnetic resonance angiography (MRA) is recommended. Proposed diagnostic algorithm: Figure 3.

TreatmentTop

Secure peripheral venous access and—if this does not delay the diagnostic process—central venous access. Monitor urine output, heart rate, BP, electrocardiography (ECG), and arterial oxygen saturation (SaO2); continue monitoring while transporting the patient to a specialist center.

1. Medical treatment: Medical treatment is used in the initial treatment and stabilization of patients with all types of aortic dissections and may be the sole treatment for uncomplicated type B dissections. (All type A and complicated type B dissections should be considered for immediate surgery [type A] or endovascular repair [type B].)

1) Administer IV morphine for pain control.

2) Quickly lower BP (systolic BP to 100-120 mm Hg after excluding severe aortic regurgitation):

a) Administer an IV beta-blocker, such as propranolol 1 mg every 3 to 5 minutes until the target BP is achieved (up to a maximum of 10 mg) then every 4 to 6 hours; or esmolol (dosage: see Table 3 in Essential Hypertension). In patients with asthma or severe chronic obstructive pulmonary disease, replace beta-blockers with calcium channel blockers (or short-acting esmolol).

b) In some patients it may be necessary to add IV nitroglycerin, and if this is ineffective, you may use IV sodium nitroprusside (agents and dosage: see Table 3 in Essential Hypertension). In case of refractory hypertension, you may add enalapril (start from 0.625-1.25 mg IV every 6 hours [up to a maximum of 5 mg]).

2. Invasive treatment: Urgent surgical intervention is the treatment of choice in the majority of patients with type A dissection (perform CT only in hemodynamically stable patients when the study does not delay transfer to a cardiac surgery center). Complicated type B dissections are those defined as ≥1 of the following: end-organ malperfusion (bowel, renal, spinal cord, lower extremity ischemia), rapid aortic expansion, refractory chest or back pain, uncontrolled hypertension despite adequate pharmacotherapy, signs of rupture (hemothorax, expanding periaortic or mediastinal hematoma). Treatment options for complicated type B dissections include endovascular stenting of the aortic entry tear and fenestration or stenting of branch vessels to restore perfusion in any ischemic organs. Open surgical repair of complicated type B dissections is increasingly rare and generally happens when endovascular repair is unavailable or not feasible.

ComplicationsTop

Aortic regurgitation (in patients with ascending aortic dissection), ischemia of the extremities and internal organs, stroke, paraplegia, intestinal ischemia, and aortic rupture.

Tables and FiguresTop

Figure 3.19-1. Multislice computed tomography (CT) in a patient with acute ascending aortic dissection: A, pericardial effusion (white arrow) and pleural effusion (red arrows); B, dissected ascending aorta (the arrow marks the dissection flap). Figure courtesy of Dr Jerzy Walecki.

Figure 3.19-2. Descending aortic dissection. Transesophageal color Doppler ultrasonography reveals flow from the true lumen through the intimal tear (arrow). Figure courtesy of Dr Marek Krzanowski.

Figure 3.19-3. Diagnosis of suspected acute aortic syndrome. Based on Eur Heart J. 2014;35(41):2873-926.