Aortic dissection: Etiology, Pathogenesis, Classification, Diagnosis, Treatment methods

Aortic dissection (dissection) is an acute condition characterized by rupture of the inner sheath (intima) of the aorta with subsequent penetration of blood into the middle layer (media) and formation of a false lumen. This condition is associated with a high risk of aortic rupture, acute organ ischemia and death and requires urgent diagnosis and treatment.

Epidemiology

• Frequency: 3-6 cases per 100,000 people per year. However, autopsy data suggest that the actual prevalence is higher.
• Gender: Men are affected more often than women (≈2:1).
• Age: Peak at 60-70 years (for sporadic forms); syndromic forms (e.g., in Marfan syndrome) at younger ages (20-40 years).
• Geography/race: African Americans demonstrate earlier age of onset and higher mortality; incidence is higher in countries with poorly controlled arterial hypertension.

Etiology

• Arterial hypertension is the main factor (up to 80% of cases).
• Atherosclerosis: weakening of the intima due to inflammation and damage.
• Hereditary connective tissue syndromes: Marfan syndrome (impaired fibrillin synthesis); Ehlers-Danlo syndrome (connective tissue weakness); Loeys-Dietz syndrome (mutations in TGF-β genes).
• Bicuspidal aortic valve.
• Coarctation of the aorta.
• Pregnancy (especially the third trimester).
• Iatrogenic causes – catheterizations, surgical interventions.
• Trauma (high-energy, more often thoracic).
• Inflammatory diseases (vasculitides) – for example, gigantocellular arteritis.
• Infections (such as syphilis or mycotic lesions).

Pathogenesis

• The primary link is rupture of the aortic intima due to high systolic pressure or disruption of the structural integrity of the wall.
• Entry of blood into the media (middle layer) → formation of a false channel between the layers of the aortic wall.
• The longitudinal spread of dissection is proximal or distal to the site of primary rupture, often involving aortic branches.

Possible Consequences:

• Compression of the true lumen → ischemia of organs (kidneys, liver, intestines, limbs, brain).
• If spread to the aortic root, it may cause acute aortic valve insufficiency or acute myocardial ischemia with involvement of the coronary artery orifices.
• Rupture of the outer layer (adventitia) → massive bleeding into cavities (pericardium, pleura, retroperitoneum).
• Formation of repeated inlets – maintains circulation in the false channel.

Markers of remodeling:

• Activation of metalloproteinases (MMP-2, -9), collagen and elastin degradation.
• Endothelial dysfunction and inflammatory response (TNF-α, IL-6).

Classification of aortic dissection

Stanford classification

• Type A: affects the ascending aorta (with or without involvement of the aortic arch).
• Type B: limited to the descending aorta.

Due to the fact that this classification did not take into account isolated lesions of the aortic arch or lesions of the arch in combination with the descending branch, the concept of a third type, Non-A non-A and non-B (non-A non-B), was proposed in 2019.

DeBakey classification

• Type I: dissection from the ascending aorta to the aortic arch or below.
• Type II: limited to the ascending aorta.
• Type III: lesion of the descending aorta only (IIIa – up to the diaphragm, IIIb – spreading below).

3D Models of aortic dissection:

Aortic dissection type I

Aortic dissection type II

Aortic dissection type IIIa

Aortic dissection type IIIb

By duration

• Acute: first 14 days from onset.
• Subacute: 15 to 90 days.
• Chronic: more than 90 days.

Clinical Manifestations

Symptomatology depends on the localization of the dissection, the degree of involvement of aortic branches and the presence of complications.

• Acute pain: sharp, retching, “dagger” pain, may be migratory, localization depends on the location of the dissection (type A: chest or back pain; type B: low back or abdominal pain).
• Hypotension or shock with massive bleeding.
• Asymmetry of pulse and BP in the arms.
• Neurological disorders: weakness, loss of consciousness, symptoms of cerebral ischemia.
• Cardiac symptoms: acute myocardial infarction (coronary artery involvement), acute aortic valve insufficiency.
• Renal insufficiency: impaired blood supply to the kidneys (oliguria/anuria).
• Intestinal ischemia: abdominal pain, bloody diarrhea.
• Cardiac tamponade with bleeding into the pericardial cavity.
• Acute limb ischemia due to arterial occlusion.

Diagnosis

Physical examination (BP difference at the extremities; pulse deficit; aortic regurgitation murmur).

Lab Tests:

• Elevation of D-dimer levels in the first few hours.
• Biomarkers of myocardial injury (troponin, CK-MB).
• Renal, liver enzymes, lactate – in organ ischemia.
• General and biochemical blood tests – anemia, inflammation.

Instrumental studies:

• CT angiography (gold standard): high sensitivity and specificity (>95%). Rapid and accurate detection of dissection, identification of false and true channels, primary inlet, extent of dissection, areas of malperfusion.
• Transesophageal ultrasound: High sensitivity, especially for type A. Allows evaluation of the intimal flap, size of the ascending aorta, aortic insufficiency, signs of ischemia, pericardial effusion.
• MRI: An alternative to CT for chronic stratification or contraindications to contrast. High sensitivity, especially for assessing dynamics.

Treatment of aortic dissection

Conservative treatment (more common for type B):

Optimal antihypertensive, antianginal, and hypolipidemic therapy. In the acute period, constant monitoring in intensive care.

• β-blockers (esmolol, metoprolol) – first line: they reduce HR and dp/dt (decrease the force and velocity of blood hitting the wall).
• Sodium nitroprusside, uropidil, clonidine, nitroglycerin – BP reduction (after β-blockers) to 100-120 mmHg. Art.
• Morphine – anesthesia and decreased sympathetic activation.

For stable uncomplicated dissections type B:

• BP and HR monitoring.
• Regular follow-up (CT/MR monitoring).
• Secondary prevention: antihypertensive, risk factor modification (smoking, cholesterol, diabetes).

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Surgical treatment (more common for type A):

1. Open surgery (usually using a ventilator and hypothermia techniques).

• The affected segment of the aorta is resected with subsequent suturing of the prosthesis.
• If the aortic arch is involved, the brachiocephalic arteries are reimplanted into the prosthesis (if the brachiocephalic arteries themselves are involved in the dissection process, they are also prosthetized).
• If the dissection spreads to the aortic valve, aortic valve replacement is performed, and in some cases valve-preserving surgery is possible.
• If spread to the coronary artery orifices, reimplantation or aortocoronary bypass surgery may be performed.
• When spreading to the arch and descending branch, a hybrid prosthesis (Frozen Elephant Trunk) is possible in some cases.

2. Endovascular intervention (TEVAR): Placement of a stent graft to isolate a false lumen (especially in organ malperfusion). Suitable for stable patients with complications or type B with uncontrolled hypertension/pain and/or at risk of rupture.
3. In case of aortic rupture or cardiac tamponade, immediate surgery is required.