Aortic dissection

Epidemiology

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Etiology

• Hypertension: Most important risk factor (70% of cases).
• Connective Tissue Disorders: Marfan syndrome, Ehlers-Danlos (look for young patient, tall stature).
• Other: Bicuspid aortic valve, Cocaine use, Trauma (deceleration injury), 3rd Trimester Pregnancy (blood volumn and cardiac output increase 50%). c

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Pathophysiology

Feature	Stanford Type A	Stanford Type B
Location	Involves Ascending Aorta	Descending Aorta ONLY
Pain	Anterior chest	Back / Interscapular
Key Risks	Marfan, Bicuspid AoV, HTN	Chronic HTN
Complications	Tamponade, AR, MI, Stroke	Bowel/renal ischemia, Paraplegia
Initial Mgmt	IV BB (target SBP 100-120)	IV BB (target SBP 100-120)
Definitive Mgmt	Emergent Surgery	Medical (Surgery only if complicated)

Characteristic	Aortic aneurysm (AAA)	Aortic Dissection
Definition	Localized dilation of abdominal aorta >3cm	Tear in aortic wall creating false lumen
Risk Factors	Smoking (most important), male, hypertension, age >65, family history	Hypertension (most important), Marfan syndrome, bicuspid valve, pregnancy
Pathophysiology	Progressive weakening of arterial wall due to elastin degradation and inflammation; atherosclerosis leads to oxidative stress and matrix metalloproteinase activation	Intimal tear allows blood to enter media, creating false lumen; can be triggered by hypertensive crisis or inherited connective tissue disorders
Onset	Gradual	Sudden, acute
Pain	Usually asymptomatic; may have dull abdominal/back pain	Severe, tearing chest/back pain; migrating
Physical Exam	Pulsatile abdominal mass	Unequal pulses, BP differences between arms
Complications	Rupture with hemorrhagic shock	Organ ischemia, tamponade, aortic rupture
Imaging	Ultrasound, CT with contrast	CT angiogram, TEE
Treatment	Endovascular repair (EVAR) or open surgery if >5.5cm	Emergency surgery (Type A), medical management (Type B)
Mortality	80% if ruptured; 5% with elective repair	50% at 48h without treatment (Type A)

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Clinical features

• Pain: Sudden onset, severe, “tearing” or “ripping” quality. Radiates to back (interscapular).
• PE:
  • BP Asymmetry: >20 mmHg diff in SBP between arms.
  • Pulse Deficit: Weak/absent carotid, radial, or femoral pulses. c
  • AR Murmur: New early diastolic decrescendo murmur (if dissection involves aortic root).
  • Neuro: Syncope, focal deficits (stroke), paraplegia (spinal cord ischemia).
  • Horner Syn: Ptosis/miosis/anhidrosis (compression of symp chain).

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Diagnostics

• Chest X-ray (CXR): Often the first imaging study; may show a widened mediastinum (>8 cm).
• CT Angiography (CTA): Gold standard for diagnosis in hemodynamically stable patients. Shows intimal flap and true/false lumens.
• Transesophageal Echocardiogram (TEE): Best test for hemodynamically unstable patients c ; can be done at the bedside. Also excellent for evaluating aortic regurgitation and pericardial effusion/tamponade.
• ECG: May be normal or show non-specific ST/T wave changes. Can show STEMI if a coronary artery is occluded (esp. the RCA). c

Pathology

• Cystic medial degeneration: a degeneration (necrosis) of large blood vessels such as the aorta.
  • Seen in disorders that cause increased arterial wall stress (e.g., hypertension, coarctation of the aorta) as well as connective tissue disorders (especially Ehlers-Danlos syndrome and Marfan syndrome)
  • Can lead to aortic aneurysm and aortic dissection
  • Histopathology
    • Loss, thinning, disorganization, and fragmentation of elastic tissue in the media
    • Accumulation of mucoid extracellular matrix
    • Loss of smooth muscle nuclei

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Treatment

1. Stabilize / Medical Management (Step 1 for ALL pts):
   • 1st Line: IV Beta-blockers (e.g., Labetalol, Esmolol) to strictly ↓ HR (<60 bpm) and ↓ LV dP/dt (shearing force). t
   • 2nd Line: Add IV vasodilator (e.g., Nitroprusside) to ↓ SBP (target 100-120 mmHg) ONLY AFTER HR is controlled by beta-blockade (prevents reflex tachycardia, which worsens dissection).
   • Adequate analgesia (IV Morphine) to ↓ sympathetic output.
2. Definitive Therapy:
   • Type A (Ascending): Urgent open surgical repair.
   • Type B (Descending) Uncomplicated: Medical management (strict BP/HR control).
     • The descending aorta supplies the intercostal arteries, which feed the Artery of Adamkiewicz (supplying the anterior spinal cord).
     • Surgical intervention carries high risk of paraplegia (Artery of Adamkiewicz damage)
   • Type B (Descending) Complicated (e.g., malperfusion syndrome, rupture, rapid expansion): Endovascular stenting (TEVAR) or surgery.

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Complications

• Cardiac Tamponade: Most common cause of death in Type A. c
• Acute Aortic Regurgitation: Can lead to acute heart failure/cardiogenic shock.
• Organ Ischemia (Malperfusion Syndromes):
  • Brain: Stroke (carotid artery).
  • Kidneys: AKI (renal artery).
  • Gut: Mesenteric ischemia (SMA/IMA).
  • Spinal cord: Anterior cord syndrome/paraplegia (Artery of Adamkiewicz).