What is aortic dissection, including its pathophysiology, classification, and management?

Aortic Dissection: Definition, Pathophysiology, Classification, and Management

Definition and Pathophysiology

Aortic dissection is a disruption of the medial layer of the aortic wall caused by intramural bleeding, resulting in separation of the wall layers and formation of a true lumen and false lumen, with or without communication between them. 1

The pathophysiologic sequence begins when blood penetrates from the aortic lumen into the media through either an intimal tear or rupture of vasa vasorum, creating a dissection plane within the media. 1 This process can propagate either antegrade or retrograde along the aorta. 1 The inflammatory response to blood within the media initiates necrosis and apoptosis of smooth muscle cells and degeneration of elastic tissue, which increases the risk of medial rupture. 1

Key Pathophysiologic Features:

• Intimal disruption occurs due to hemodynamic stressors, connective tissue disorders, or anatomic abnormalities such as bicuspid aortic valve 1
• Medial layer weakness allows blood to track between layers, creating the false lumen 2, 3
• Potential complications include external rupture if adventitial layers are compromised, coronary artery obstruction, tamponade, aortic valve regurgitation, and malperfusion syndromes 1

Classification Systems

Stanford Classification (Primary Clinical System)

The Stanford classification is the most clinically practical system, dividing dissections into Type A (involving the ascending aorta) and Type B (not involving the ascending aorta), which directly guides surgical versus medical management decisions. 4

• Type A: Involves the ascending aorta regardless of the site of origin; requires immediate surgical intervention due to high risk of rupture, tamponade, and aortic valve insufficiency 1, 4
• Type B: Does not involve the ascending aorta; typically managed medically unless complications occur 1, 4

DeBakey Classification (Anatomical Detail)

The DeBakey system provides more anatomical specificity by categorizing dissections based on the origin of the intimal tear and extent of propagation: 1, 4

• Type I: Originates in the ascending aorta and propagates distally to include at least the aortic arch and typically the descending aorta 4
• Type II: Originates in and is confined to the ascending aorta 4
• Type III: Originates in the descending aorta and propagates distally (subtypes IIIa and IIIb based on extent) 4

Relationship between systems: Stanford Type A includes DeBakey Types I and II, while Stanford Type B corresponds to DeBakey Type III. 4

Acute Aortic Syndrome Classification

The European Society of Cardiology recognizes five classes of acute aortic syndrome based on pathologic features: 1

• Class 1: Classic dissection with intimal flap between true and false lumen 1
• Class 2: Intramural hematoma/hemorrhage without visible intimal tear (10-30% of cases) 1, 5
• Class 3: Subtle/discrete dissection without hematoma 1
• Class 4: Penetrating aortic ulcer following plaque rupture 1
• Class 5: Iatrogenic or traumatic dissection 1

Temporal Classification

Dissections are further categorized by chronicity: 1

• Acute: <14 days
• Subacute: 15-90 days
• Chronic: >90 days

Epidemiology and Mortality

Patients with acute Type A dissection suffer double the mortality of those with Type B dissection (25% versus 12%, respectively). 1, 5 The incidence of aortic dissection is approximately 6 per 100,000 persons per year, with higher rates in men and increasing incidence with age. 1 In-hospital mortality can reach 27% even under optimal conditions. 1 Mortality increases by 1% per hour in untreated Type A dissections, highlighting the critical importance of prompt diagnosis and intervention. 4

High-Risk Features:

• Hypertension present in 65-75% of cases, often poorly controlled 5
• Genetic connective tissue disorders (Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlos Type IV) 1, 5
• Aortic regurgitation accompanies 40-75% of Type A dissections and is the second most common cause of death after rupture 1

Management

Type A Dissection (Ascending Aorta Involvement)

Type A dissections require immediate surgical intervention to prevent fatal complications including rupture, cardiac tamponade, and severe aortic insufficiency. 4, 6

Immediate Management:

• Urgent surgery is the definitive treatment (Class I recommendation) 1, 4
• Blood pressure control while preparing for surgery to reduce hemodynamic stress 1, 7
• Heart rate control to decrease velocity of left ventricular contraction 7
• Transfer to specialized aortic center if not already at one 2

Surgical Approach:

• Open surgical repair is the gold standard for proximal dissections and arch involvement 3
• Total aortic replacement may be necessary depending on extent 7
• Surgical success rates now exceed 90% when performed promptly 7

Type B Dissection (Descending Aorta, No Ascending Involvement)

Type B dissections are managed medically unless complications develop, as surgical intervention has not shown benefit for uncomplicated cases. 1, 6

Medical Management (Uncomplicated Type B):

• Strict blood pressure control to target systolic BP 100-120 mmHg 7
• Heart rate control to reduce aortic wall stress 7
• Pain control 5
• Close surveillance for development of complications 6

Indications for Intervention (Complicated Type B):

Urgent endovascular repair (TEVAR) or surgery is indicated for: 5, 6

• Actual or impending rupture
• Malperfusion syndromes (visceral, renal, or limb ischemia)
• Persistent or recurrent pain despite medical therapy
• Uncontrolled hypertension
• Rapid expansion of false lumen

Intramural Hematoma Management

Type A intramural hematoma requires urgent surgery, while Type B intramural hematoma is initially managed medically under close surveillance. 5

• Medical treatment includes pain and blood pressure control for all patients 5
• Endovascular repair (TEVAR) should be considered for complicated Type B intramural hematoma 5
• Intramural hematoma can progress to classic dissection in 28-47% of patients 1

Critical Diagnostic Approach

Computed tomography angiography (CTA) without delay is the initial test of choice for suspected aortic dissection. 5

Diagnostic Modalities:

• CTA: Sensitivity 96%, diagnostic technique of choice 1, 5
• Transesophageal echocardiography (TEE): Useful in hemodynamically unstable patients who cannot be transported 5
• Focused transthoracic echocardiography + ECG: Rapid initial evaluation at bedside 5
• MRI/MRA: May be useful when differentiating intramural hematoma from atherosclerotic thickening 5

Common Pitfalls and Caveats

The misdiagnosis of aortic dissection is a substantial medicolegal concern due to varied clinical presentations and the rarity of the condition. 1

• Clinical presentation varies: While chest pain is most frequent (80%), back pain occurs in 40% and abdominal pain in 25% 5
• Pain characteristics: Abrupt onset, severe intensity, tearing or ripping sensation 5
• Do not delay imaging for risk stratification scores; proceed directly to CTA if clinical suspicion exists 5
• Hemodynamic instability: Perform TEE at bedside rather than transporting unstable patients 5
• Aortic regurgitation: Present in up to 75% of Type A cases and significantly worsens prognosis 1

Long-Term Follow-Up

Diligent long-term follow-up is essential, including blood pressure control, monitoring residual aorta size, and surveillance for redissection, aneurysmal formation, or rupture. 7

• Continue antihypertensive therapy indefinitely 7
• Serial imaging to monitor aortic dimensions 7
• Long-term survival after appropriate treatment now exceeds 50% at 10 years 7