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Diseases of the Aorta

Chapter 291 | Part 6: Disorders of the Cardiovascular System · Part 6 – Cardiovascular Disorders · Chapter 291

Key Clinical Points

  1. A true aneurysm involves all three layers of the vessel wall; a pseudoaneurysm involves only the adventitia (intimal and medial layers are disrupted).
  2. Surgical thresholds for thoracic aneurysms: ≥4.5 cm (ascending), ≥5.5 cm (descending), and ≥5.0 cm (abdominal in women).
  3. Acute aortic dissection presents with sudden, severe, tearing pain that often migrates with propagation of the dissection.
  4. Medical management for Marfan/Loeys-Dietz includes β-adrenergic blockers (e.g., atenolol) or angiotensin receptor antagonists (e.g., losartan).
  5. Abdominal aortic aneurysm (AAA) screening in women aged ≥65 who have ever smoked provides a 42% reduction in aneurysm-related death.
  6. Acute dissection management targets heart rate 60–80 beats/min and systolic blood pressure ≤120 mmHg using β-adrenergic blockers (esmolol, propranolol) and vasodilators (sodium nitroprusside).
  7. Risk of rupture for thoracic aneurysms is 2–3% per year for those ≥6 cm in diameter.
  8. Pulse delay or pressure differential between upper and lower extremities suggests aortic coarctation.
  9. Genetic testing is recommended for patients <60 years old with ascending thoracic disease or specific features (Marfan, Loeys-Dietz, vEDS).
  10. Endovascular repair of AAA has lower short-term morbidity but comparable long-term mortality to open surgery.

DEFINITION & OVERVIEW

• Aneurysm Definition: A true aneurysm involves all three layers of the vessel wall and is distinguished from a pseudoaneurysm, in which the intimal and medial layers are disrupted and the dilated segment of the aorta is lined by adventitia only and, at times, by perivascular clot. • Morphological Classification: ◦ Fusiform: Affects the entire circumference of a segment of the vessel → results in a diffusely dilated artery. ◦ Saccular: Involves only a portion of the circumference → results in an outpouching of the vessel wall. • Anatomical Classification: ◦ Thoracic: Located in the chest; descending thoracic aneurysms contiguous with infradiaphragmatic segments are referred to as thoracoabdominal aortic aneurysms. ◦ Abdominal: Located below the diaphragm.

Congenital Anomalies

• Clinical Presentation: Symptoms such as dysphagia, stridor, and hypertension may occur if an anomaly causes a ring around or otherwise compresses the esophagus or trachea. • Common Anomalies: Double aortic arch; right-sided aortic arch with an aberrant left subclavian artery; Kommerell diverticulum (anatomic remnant of a right aortic arch). • Diagnosis: Typically detected during catheter-based procedures; confirmed by CT or MR angiography.

EPIDEMIOLOGY

• Demographics: ◦ More common in males than in females. ◦ Incidence increases with age. • Risk Factors: ◦ Cigarette smoking (potent modifiable risk factor). ◦ Atherosclerosis: ≥90% of all abdominal aortic aneurysms >4.0 cm are related to atherosclerotic disease. • Screening Guidelines: ◦ Men: 1–2% of men aged >50 years have AAA ≥4.0 cm. ◦ Women: Screening recommended for those aged ≥65 years who have ever smoked; this results in a 42% reduction in aneurysm-related death.

ETIOLOGY & PATHOPHYSIOLOGY

• General Mechanism: Degraded or abnormal production of structural components (elastin and collagen) due to inflammation, oxidative stress, proteolysis, and biomechanical wall stress. • Degenerative & Sporadic: ◦ Primarily atherosclerosis. ◦ Medial Degeneration: Loss of collagen/elastic fibers in the tunica media; results in fusiform aneurysms (Marfan, Loeys-Dietz, vEDS, bicuspid aortic valve, Turner syndrome). • Heritable & Genetic Syndromes: ◦ Marfan Syndrome: Mutation in fibrillin-1 → increased signaling by transforming growth factor β (TGF-β). ◦ Loeys-Dietz Syndrome: Mutations in TGF-β isoforms (TGFB2, TGFB3), receptors (TGFBR1, TGFBR2), or SMAD3. ◦ vEDS: Mutation in type III procollagen (COL3A1). ◦ Other Genetic Factors: ACTA2, MYH11, MYLK, PRKG1. • Infective & Vasculitis: ◦ Infectious: Syphilis (ascending/arch), Tuberculosis (thoracic), Mycotic (saccular; often at atherosclerotic plaques). ◦ Vasculitis: Takayasu arteritis, Giant cell arteritis, IgG4-related systemic disease, Isolated aortitis. ◦ Spondyloarthropathies: Ankylosing spondylitis, rheumatoid arthritis, psoriatic arthritis, relapsing polychondritis, and reactive arthritis (associated with dilation of the ascending aorta). ◦ Other Syndromes: Behçet syndrome, Cogan syndrome. • Trauma & Acute Syndromes: ◦ Penetrating or nonpenetrating chest trauma (typically descending thoracic). ◦ Chronic aortic dissections or acute syndromes (intramural hematoma, penetrating atherosclerotic ulcer) leading to wall weakening.

CLINICAL FEATURES

• General Aneurysm Symptoms: ◦ Often asymptomatic. ◦ Large aneurysms: Chest pain, shortness of breath, cough, hoarseness, and dysphagia (due to compression/erosion). ◦ Ascending aorta dilation → potential congestive heart failure from aortic regurgitation. ◦ Abdominal: Palpable, pulsatile, expansile, and nontender mass; pain is a harbinger of rupture and represents a medical emergency. • Aortic Dissection Classification: ◦ Stanford: Type A (ascending aorta); Type B (descending aorta). ◦ DeBakey: Type I (ascending to descending); Type II (ascending/transverse only); Type III (descending only). • Acute Aortic Dissection Symptoms: ◦ Pain: Sudden, very severe, tearing; often migrates with propagation of the dissection. ◦ Associated Symptoms: Diaphoresis, syncope, dyspnea, weakness. ◦ Complications: ◦ Hemopericardium and cardiac tamponade (Type A). ◦ Acute aortic regurgitation (>50% of proximal dissections) → bounding pulses, wide pulse pressure, diastolic murmur. ◦ Neurologic: Hemiplegia/hemianesthesia (carotid artery obstruction), paraplegia (spinal cord ischemia). ◦ Local Compression: Horner's syndrome, superior vena cava syndrome, hoarseness, dysphagia, and airway compromise.

DIFFERENTIAL DIAGNOSIS

• Aortic Dissection vs. Myocardial Infarction: ◦ Key Test: Electrocardiogram (ECG). ◦ Logic: ECG showing no evidence of myocardial ischemia helps differentiate the two.

INVESTIGATIONS & DIAGNOSIS

  1. Clinical Clues: • Pulse delay or pressure differential between upper and lower extremities → suspect aortic coarctation.
  2. Imaging for Congenital Anomalies: • Confirmed by CT or MR angiography.
  3. Imaging for Aneurysms: • CT or MRI used to assess size, morphology, and surgical planning.

MANAGEMENT & TREATMENT

  1. Medical Therapy: • Marfan/Loeys-Dietz: β-adrenergic blockers (e.g., atenolol) or angiotensin receptor antagonists (e.g., losartan) to reduce aortic root enlargement.
  2. Acute Aortic Dissection Management: • Immediate Goals: Reduce heart rate to 60–80 beats/min and systolic blood pressure to ≤120 mmHg. • Agents: β-adrenergic blockers (e.g., esmolol, propranolol) and vasodilators (e.g., sodium nitroprusside).
  3. Surgical & Endovascular Repair: • Ascending Thoracic Aneurysm: Surgery indicated if diameter ≥4.5 cm. • Descending Thoracic Aneurysm: Surgery indicated if diameter ≥5.5 cm. • Abdominal Aortic Aneurysm (AAA): Surgery indicated if diameter ≥5.0 cm in women. • Endovascular Repair (EVAR): Lower short-term morbidity; comparable long-term mortality to open surgical reconstruction.

PROGNOSIS & COMPLICATIONS

• Rupture Risk: ◦ Thoracic aneurysms ≥6 cm in diameter: 2–3% per year. • Acute Rupture: Life-threatening; requires emergency operation or endovascular repair.

SPECIAL CONSIDERATIONS

• Pregnancy: (Refer to specific clinical guidelines for management of aortic pathology in pregnancy). • Genetic Testing: ◦ Recommended for patients with ascending thoracic aortic disease who are <60 years old or have features of Marfan, Loeys-Dietz, or vEDS.

KEY PEARLS & CLINICAL TRAPS

• Surgical Thresholds: ◦ Ascending: ≥4.5 cm ◦ Descending: ≥5.5 cm ◦ Abdominal: ≥5.0 cm (women) • Acute Dissection Management: Target HR 60–80 and SBP ≤120 mmHg immediately using esmolol, propranolol, or sodium nitroprusside. • Screening Benefit: AAA screening in high-risk women provides a 42% reduction in aneurysm-related death. • Rupture Risk: Thoracic aneurysms ≥6 cm have a 2–3% annual rupture risk.

Reference Tables

TABLE 291-1 Diseases of the Aorta: Etiology and Associated Factors Aortic aneurysm

Harrison's 22e, p.2166

  • Aortic aneurysm
  • Degenerative/sporadic
  • Aging
  • Cigarette smoking
  • Hypercholesterolemia
  • Hypertension
  • Atherosclerosis
  • Heritable
  • Marfan syndrome
  • Loeys-Dietz syndrome
  • Ehlers-Danlos syndrome type IV
  • Aneurysm-osteoarthritis syndrome
  • Smooth muscle dysfunction syndrome
  • Familial (nonsyndromic)
  • Congenital
  • Bicuspid aortic valve
  • Turner syndrome
  • Aortic coarctation
  • Fibromuscular dysplasia
  • Chronic aortic dissection
  • Aortitis (see below)
  • Infective (see below)
  • Trauma
  • Acute aortic syndromes (aortic dissection, acute intramural hematoma,
    penetrating atherosclerotic ulcer)
  • Degenerative disorders (see above)
  • Heritable/disorders (see above)
  • Congenital disorders (see above)
  • Hypertension
  • Aortitis (see below)
  • Pregnancy
  • Trauma
  • Aortic occlusion
  • Atherosclerosis
  • Thromboembolism
  • Aortitis
  • Vasculitis
  • Takayasu’s arteritis
  • Giant cell arteritis
  • IgG4-related aortitis
  • Isolated aortitis
  • Rheumatic
  • Rheumatoid aortitis
  • HLA-B27–associated spondyloarthropathies
  • Behçet syndrome
  • Cogan syndrome
  • Infective
  • Syphilis
  • Tuberculosis
  • Mycotic (Salmonella, staphylococcal, streptococcal, fungal)