Aortic Dissection

Detailed Overview

The condition is highly lethal. As the false lumen extends longitudinally along the aorta, it can compress or tear off branch arteries, causing ischemia to the brain, kidneys, spinal cord, or intestines. Dissections involving the ascending aorta (Stanford Type A) can quickly lead to death via retrograde extension causing aortic valve rupture, acute severe aortic regurgitation, coronary artery occlusion, or rupture into the pericardial space causing fatal cardiac tamponade. Stanford Type B involves only the descending aorta. The primary drivers are chronic hypertension and structural weakness of the aortic media (cystic medial necrosis).

Epidemiology & Demographics

Incidence is roughly 3 per 100,000 person-years. Most commonly affects men in their 60s and 70s. Younger patients are usually affected due to underlying connective tissue disorders.

Etiological Mechanism

The predominant underlying cause is chronic poorly controlled hypertension. Connective tissue disorders (Marfan syndrome, Ehlers-Danlos), bicuspid aortic valve, and prior aortic surgery are significant structural etiologies.

Primary Causes

Chronic Uncontrolled Hypertension (72% of cases)

Marfan Syndrome (fibrillin-1 mutation)

Bicuspid Aortic Valve

Iatrogenic (post-cardiac catheterization or CABG)

• Hypertension: Increases continuous mechanical wall stress on the aorta.
• Atherosclerosis: Causes penetrating ulcers that can serve as an entry point for a dissection.
• Cocaine use: Causes severe, abrupt transient spikes in blood pressure.
• Pregnancy (3rd trimester): Hormonal changes and increased blood volume increase aortic wall stress.

1. An initial intimal tear occurs, often at the right lateral wall of the ascending aorta where hydraulic shear stress is highest. 2. Systolic blood pressure forces blood into the diseased tunica media (cystic medial degeneration). 3. The pulsatile force creates and propagates a 'false lumen' alongside the 'true lumen'. 4. The expanding false lumen compresses the true lumen, creating malperfusion syndromes as branch arteries (e.g., renal, mesenteric, spinal) are occluded. 5. Retrograde dissection toward the heart can shear off the coronary arteries (causing STEMI) or rupture into the pericardium (tamponade). Antegrade dissection can rupture through the adventitia into the pleural cavity, causing exsanguination.

Characteristic Clinical Presentation

• Chest/Back Pain: Sudden onset of severe, 'tearing', 'ripping', or 'sharp' pain in the anterior chest (Type A) or radiating to the interscapular back (Type B). Maximal intensity at onset.
• Syncope: Fainting due to hypotension, tamponade, or occlusion of cerebral vessels.
• Neurologic Deficits: Stroke-like symptoms (hemiparesis, aphasia) or paraplegia due to spinal cord ischemia.

Physical Examination Signs

• Pulse Deficit
• Diastolic Murmur
• Hypotension/Shock

• Cardiac Tamponade: Bleeding into the pericardial sac compressing the heart; the most common cause of death in Type A.
• Acute Myocardial Infarction: Usually right coronary artery occlusion, mimicking a primary heart attack.
• Mesenteric Ischemia: Occlusion of the superior mesenteric artery leading to bowel necrosis.

Diagnostic Criteria & Guidelines

Diagnosis is confirmed via imaging demonstrating an intimal flap separating two distinct lumens within the aorta.

Differential Diagnosis

• Acute Myocardial Infarction (STEMI/NSTEMI)
• Pulmonary Embolism
• Esophageal Rupture (Boerhaave Syndrome)
• Acute Pericarditis

Laboratory Tests & Biomarkers

• D-dimer: Typically highly elevated (>500 ng/mL). A normal D-dimer makes dissection highly unlikely, though not impossible.
• Troponin: May be elevated if coronary ostia are involved, complicating differentiation from primary MI.
• Creatinine: Elevated if renal artery perfusion is compromised.

Imaging Modalities & Findings

• CT Angiography (CTA) of Chest/Abdomen/Pelvis: The gold standard. Visualizes the intimal flap, extent of dissection, true vs. false lumen, and branch vessel involvement.
• Transesophageal Echocardiogram (TEE): Used for unstable patients who cannot go to the CT scanner; excellent for visualizing ascending aorta and aortic valve.

• Stanford Type A
  Involves the ascending aorta, regardless of origin. Requires emergent open surgery.
• Stanford Type B
  Involves only the descending aorta (distal to left subclavian). Often managed medically.

Second-Line & Adjunctive Therapy

For Type B dissections with complications (malperfusion, rapid expansion, intractable pain): Thoracic Endovascular Aortic Repair (TEVAR) to stent the true lumen and seal the entry tear.

Surgical & Procedural Management

Stanford Type A is an absolute surgical emergency. Requires median sternotomy, cardiopulmonary bypass, excision of the intimal tear, and replacement of the ascending aorta with a synthetic Dacron graft (often combined with aortic valve replacement).

Recommended Lifestyle Changes

• Aggressive, lifelong blood pressure monitoring and control.
• Avoidance of heavy weightlifting or isometric exercises that spike blood pressure.

Patient Counseling & Advice

Type A survivors must understand they require lifelong imaging surveillance to monitor the residual false lumen in the descending aorta, which can form an aneurysm over time.

Follow-Up & Monitoring Schedule

Serial CT angiography at 1, 3, 6, and 12 months, then annually, to monitor for progressive aortic dilation or pseudoaneurysm formation.

Preventive Strategies

Strict management of hypertension. Prophylactic elective aortic root replacement in Marfan syndrome patients when the aortic root reaches 4.5 - 5.0 cm.

Untreated Type A has a mortality rate of 1-2% per hour for the first 48 hours. With surgery, operative mortality is 10-20%. Uncomplicated Type B treated medically has a 30-day mortality of roughly 10%.