Aortic Dissection: Causes, Pathophysiology, Clinical Features, Diagnosis, Management and Prevention

Aortic Dissection: Causes, Pathophysiology, Diagnosis and Management

~Introduction

Aortic dissection is one of the most catastrophic cardiovascular emergencies, characterized by a tear in the intimal layer of the aorta, allowing blood to enter the medial layer and create a false lumen. This condition can lead to rupture, organ ischemia, or death if not diagnosed and treated promptly. Despite advancements in imaging and surgical techniques, aortic dissection continues to carry a high mortality rate, particularly in its acute form. Understanding the pathophysiology, risk factors, clinical presentation, and management strategies is crucial for timely intervention and improved patient outcomes.

~Anatomy of the Aorta

The aorta, the largest artery in the human body, originates from the left ventricle and supplies oxygenated blood to the entire body. It is divided into the ascending aorta, aortic arch, descending thoracic aorta, and abdominal aorta. The wall of the aorta consists of three layers:

1. Intima – the innermost layer, composed of endothelial cells.

2. Media – the middle layer, rich in elastic fibers and smooth muscle.

3. Adventitia – the outermost connective tissue layer.

Aortic dissection typically begins with a tear in the intima, which allows blood to penetrate into the media, splitting it longitudinally to form a false lumen parallel to the true lumen.

~Classification of Aortic Dissection

Two major classification systems are used to categorize aortic dissections — Stanford and DeBakey.

1. Stanford Classification

• Type A: Involves the ascending aorta (regardless of the site of the tear).

• Type B: Involves only the descending aorta (distal to the left subclavian artery).

2. DeBakey Classification

• Type I: Originates in the ascending aorta and extends to at least the aortic arch and often beyond.

• Type II: Confined to the ascending aorta.

• Type III: Originates in the descending aorta and extends distally (IIIa limited to thoracic aorta, IIIb extends below diaphragm).

The Stanford classification is more commonly used clinically because it directly guides management—Type A dissections typically require surgery, while Type B may be managed medically unless complications arise.

~Epidemiology

Aortic dissection is relatively rare, with an estimated incidence of 3 to 5 cases per 100,000 persons per year. It predominantly affects men, with a male-to-female ratio of about 2:1, and is most common in individuals between 50 and 70 years of age. However, younger patients with connective tissue disorders such as Marfan syndrome or Ehlers-Danlos syndrome are also at risk.

Mortality remains high — untreated acute Type A dissections have a mortality rate of nearly 1% per hour during the first 48 hours and 50% within the first week. Prompt recognition and treatment are therefore essential.

~Etiology and Risk Factors

Aortic dissection is primarily associated with conditions that weaken the aortic wall or increase mechanical stress. Major risk factors include:

1. Hypertension

The most common risk factor, present in about 70% of patients. Chronic hypertension leads to medial degeneration, making the aortic wall more susceptible to tearing.

2. Connective Tissue Disorders

Inherited diseases that cause weakening of the aortic wall:

• Marfan syndrome – fibrillin-1 gene mutation leading to cystic medial necrosis.

• Ehlers-Danlos syndrome (vascular type) – defective type III collagen.

• Loeys-Dietz syndrome – mutations in TGF-β receptor genes.

3. Atherosclerosis

Plaque formation and calcification can weaken the intima, promoting tears.

4. Iatrogenic Causes

May occur during cardiac catheterization, aortic surgery, or as a complication of aortic cannulation.

5. Trauma

Blunt chest trauma (e.g., car accidents) can cause intimal tears, especially near the aortic isthmus.

6. Pregnancy

Increased hemodynamic stress and hormonal effects on connective tissue predispose pregnant women, especially in the third trimester, to dissection.

7. Bicuspid Aortic Valve

Patients with this congenital anomaly have a higher incidence of ascending aortic aneurysm and dissection.

8. Inflammatory Diseases

Conditions like Takayasu arteritis, giant cell arteritis, and syphilitic aortitis can damage the aortic wall.

~Pathophysiology

Aortic dissection begins with a tear in the intima that allows blood to flow into the media. The high-pressure flow separates the layers of the aortic wall, creating a false lumen. This lumen may extend proximally or distally and can compress the true lumen, leading to compromised blood flow to major branches.

The dissection may propagate and lead to:

• Aortic rupture into the pericardial, pleural, or peritoneal cavity.

• Aortic regurgitation due to involvement of the aortic valve.

• Coronary artery occlusion, leading to myocardial ischemia.

• Organ ischemia if the dissection involves arterial branches supplying the brain, kidneys, or intestines.

The false lumen may thrombose, heal, or remain patent, each with distinct prognostic implications.

~Clinical Features

The presentation of aortic dissection can mimic other cardiovascular conditions, making diagnosis challenging. However, several key features help in early recognition.

1. Pain

• Nature: Sudden onset, severe, tearing or ripping in character.

• Location: Usually begins in the chest and may radiate to the back, abdomen, or neck.

• Migration: The pain may shift as the dissection progresses along the aorta.

2. Hypertension or Hypotension

• Type A dissection may present with hypotension due to pericardial tamponade or rupture.

• Type B dissection more often presents with severe hypertension.

3. Pulse Deficits and Blood Pressure Differences

Unequal pulses or blood pressure differences between arms (>20 mmHg) suggest involvement of branch vessels.

4. Neurological Symptoms

Stroke, syncope, or paraplegia can occur due to compromised blood flow to the brain or spinal cord.

5. Cardiac Findings

• Aortic regurgitation murmur due to valve involvement.

• Signs of heart failure or tamponade in advanced cases.

6. Other Organ Involvement

• Renal failure: If renal arteries are involved.

• Abdominal pain: Mesenteric ischemia.

• Limb ischemia: Occlusion of iliac or subclavian arteries.

~Complications

• Aortic rupture (fatal hemorrhage)

• Cardiac tamponade

• Aortic regurgitation

• Myocardial infarction

• Cerebrovascular accident

• Paraplegia

• Renal failure

• Bowel infarction

These complications highlight the life-threatening nature of aortic dissection and the need for rapid diagnosis and intervention.

~Diagnosis

Early and accurate diagnosis is essential. Diagnostic evaluation involves a combination of clinical suspicion and imaging studies.

1. Laboratory Tests

• D-dimer: Elevated in most cases; useful to rule out dissection in low-risk patients.

• Cardiac biomarkers: To exclude myocardial infarction.

• CBC, renal function, and coagulation profile: For preoperative evaluation.

2. Imaging Techniques

a) Computed Tomography Angiography (CTA)

• The gold standard in most emergency settings.

• Provides rapid, high-resolution images showing intimal flap, true and false lumens, and extent of dissection.

b) Transesophageal Echocardiography (TEE)

• Excellent for hemodynamically unstable patients.

• Useful for detecting proximal dissections and assessing aortic valve involvement.

c) Magnetic Resonance Angiography (MRA)

• Highly accurate and non-invasive but less practical in emergencies due to longer acquisition times.

d) Chest X-ray

• May show widened mediastinum, abnormal aortic contour, or pleural effusion but is non-specific.

e) Aortography

• Historically used but now largely replaced by non-invasive imaging.

~Differential Diagnosis

Because symptoms often mimic other acute conditions, differential diagnoses include:

• Acute myocardial infarction

• Pulmonary embolism

• Pericarditis

• Aortic aneurysm rupture

• Stroke

• Mesenteric ischemia

Clinical suspicion remains vital to distinguish dissection from these conditions.

~Management

Management depends on the type of dissection, hemodynamic stability, and presence of complications.

1. Initial Medical Management

Regardless of type, initial goals are to:

• Reduce aortic wall stress

• Control blood pressure and heart rate

Medications:

• Beta-blockers (e.g., Esmolol, Labetalol): Reduce heart rate and contractility.

• Vasodilators (e.g., Sodium nitroprusside): Used after beta-blockade to further lower blood pressure.

• Analgesia: Morphine to relieve pain and sympathetic stimulation.

Target:

• Heart rate: <60 bpm

• Systolic BP: 100–120 mmHg

2. Surgical Management

Type A Dissection

• Emergency surgery is the treatment of choice.

• Procedures include:

  • Resection of the intimal tear.

  • Replacement of the affected aorta with a graft.

  • Repair or replacement of the aortic valve if necessary.

Type B Dissection

• Medical management is preferred if uncomplicated.

• Surgical or endovascular repair (TEVAR – Thoracic Endovascular Aortic Repair) is indicated if:

  • Persistent pain or hypertension.

  • Evidence of rupture or impending rupture.

  • Malperfusion of vital organs.

3. Endovascular Repair (TEVAR)

• Minimally invasive alternative for descending dissections.

• Involves stent graft placement to seal the intimal tear and restore normal blood flow.

~Prognosis

Prognosis depends on:

• Location and extent of dissection.

• Time to diagnosis and treatment.

• Presence of complications.

Without treatment, mortality for Type A dissection approaches 90% within three months. With prompt surgical intervention, survival improves significantly, with in-hospital mortality around 20–30%.
Type B dissections have better outcomes with medical management, provided complications do not arise.

~Prevention

Preventive strategies aim to reduce risk in high-risk individuals:

• Strict blood pressure control.

• Regular imaging surveillance in patients with known aortic aneurysm or connective tissue disorders.

• Lifestyle modification: Smoking cessation, diet, and exercise.

• Genetic counseling and screening for family members in hereditary conditions.

~Follow-Up and Long-Term Management

Patients who survive an aortic dissection require lifelong follow-up:

• Regular imaging (CT/MRI) to monitor the aorta for aneurysm or recurrent dissection.

• Continued antihypertensive therapy.

• Avoidance of strenuous physical activity or heavy lifting.

~Recent Advances and Research

• Biomarker research (e.g., soluble elastin fragments, microRNAs) for early detection.

• Improved stent graft technologies for safer endovascular repair.

• Genetic studies identifying mutations associated with familial thoracic aortic disease.

• Artificial intelligence (AI) in imaging to enhance diagnostic speed and accuracy.

~Conclusion

Aortic dissection remains a medical and surgical emergency demanding immediate recognition and intervention. Despite its high mortality, advancements in imaging, surgical techniques, and endovascular therapy have significantly improved outcomes. Early diagnosis, aggressive blood pressure control, and prompt surgical or medical management are the cornerstones of successful treatment. Awareness among clinicians and patients alike can help ensure timely diagnosis, ultimately saving lives.