Harrison's Practice: Aortic Dissection

Harrison's Practice

Aortic Dissection

Definition

Uncommon, potentially life-threatening condition in which disruption of the aortic intima allows dissection of blood into vessel wall
May involve obstruction of aortic branches, dissection into the pericardial sac, or rupture into the left pleural space or retroperitoneum
Typically presents as sudden severe chest pain with radiation to the back

Epidemiology

Incidence in U.S.
- Estimated at ~3 per 100,000 per year[1]
- ~2000 cases are diagnosed annually.
- 1 in 10,000 patients are admitted to the hospital.
Age
- 75% of cases occur in persons 40–70 years of age.
- Peak incidence: sixth and seventh decades
- When seen in patients < 70 years old, often associated with Marfan’s syndrome or cocaine abuse
- When seen in patients < 40 years old, often associated with Marfan’s syndrome, Ehlers-Danlos syndrome, Turner syndrome, cocaine abuse, aortic coarctation, or a bicuspid aortic valve
Sex
- Male-to-female ratio is 3:1.
- Women who develop aortic dissection tend to be older than their male counterparts.
Race/ethnicity
- More common in black persons than white persons
- More common in white persons than Asians
Increased frequency reported during winter months and between 8 a.m. and 9 a.m.[1]

Risk Factors

Systemic hypertension coexists in 70% of patients.
Male sex
Diabetes mellitus
Cystic medial necrosis
- Marfan syndrome
- Ehlers-Danlos syndrome
Atherosclerosis
Previous cardiovascular surgery (coronary artery bypass graft, valve replacement, aortic surgery)
Congenital aortic valve anomalies
- Bicuspid valve
Coarctation of the aorta
History of aortic trauma
Otherwise normal women during the third trimester of pregnancy
Cocaine abuse
Aortic aneurysm
Previous aortic dissection
Inflammatory aortitis
- Takayasu’s arteritis
- Giant cell arteritis
Family history of dissection

Etiology

Caused by a circumferential or, less frequently, transverse tear of the intima of the aorta
- Location
  - Ascending aorta: often occurs along the right lateral wall, where hydraulic shear stress is high
  - Descending thoracic aorta: often occurs just below the ligamentum arteriosum
  - Most cases occur without preexisting aneurysm.
- Initiating event
  - Primary intimal tear with secondary dissection into the media or
  - Medial hemorrhage that dissects into and disrupts the intima
- Propagation
  - Pulsatile aortic flow dissects along the elastic lamellar plates of the aorta and creates a false lumen.
  - Usually propagates distally down the descending aorta and into its major branches, but may also propagate proximally
  - In some cases, secondary distal intimal disruption results in reentry of blood from the false to the true lumen.
Can occur as a complication of cardiac catheterization

Associated Conditions

See Risk Factors.

Symptoms & Signs

Chest pain
- Sudden onset
- Severe, sharp and tearing
- May be localized to the front or back of the chest
  - Often the interscapular region
- Typically migrates with propagation of the dissection
Diaphoresis
Syncope
Dyspnea
Weakness
Physical findings (frequencies from registry data[1])
- Reflect complications resulting from the dissection occluding the major arteries
  - Hypertension (more common in type B) or hypotension (more common in type A)
  - Loss of pulses
    - ~30 % of type A
    - ~20% of type B
  - Acute aortic regurgitation
    - ~44% of type A, 12% of type B
    - Bounding pulses
    - Wide pulse pressure
    - Diastolic murmur, often radiating along the right sternal border
    - Congestive heart failure
  - Pulmonary edema (rales)
  - Neurologic findings due to carotid artery obstruction or spinal cord ischemia
    - Hemiplegia
    - Hemianesthesia
    - Paraplegia
  - Bowel ischemia
  - Renal ischemia with hematuria
  - Myocardial ischemia
- Reflect complications resulting from compression of adjacent structures (superior cervical ganglion, superior vena cava, bronchus, esophagus) by the expanding dissection causing aneurysmal aortic dilatation
  - Horner’s syndrome
  - Superior vena cava syndrome
  - Hoarseness
  - Dysphagia
  - Airway compromise
- Cardiac tamponade
10% of patients present without typical chest pain and pulse deficits.[1]

Differential Diagnosis

Other causes of chest pain
- Myocardial infarction (MI)
  - An electrocardiogram (EEG) that shows no evidence of myocardial ischemia is helpful in distinguishing aortic dissection from MI.
  - Rarely, dissection involves the right or left coronary ostium and causes acute MI.
- Unstable angina
- Aortic aneurysm without dissection
- Pulmonary disorders
  - Pneumothorax
  - Pulmonary embolus
  - Pleurisy
  - Pneumonia
- Pericardial disease
  - Cardiac tamponade
  - Pericarditis
- GI disorders
  - Acute esophageal rupture
  - Ruptured peptic ulcer
  - Pancreatitis
  - Mesenteric ischemia
  - Cholecystitis

Diagnostic Approach

A high index of suspicion is important in:
- Patients with evolving signs and symptoms
- Patients with simultaneous multiple neurologic and vascular complaints
- Up to 30% of patients with dissection are initially suspected to have other conditions.[2]
Transesophageal echocardiography, CT, and MRI are the diagnostic procedures of choice over contrast aortography.
- Their relative utility depends on availability and expertise in individual institutions as well as on the hemodynamic stability of the patient.
- CT and MRI are less suitable for unstable patients; echocardiography should be the initial test in these patients.
- CT has advantage of being able to exclude other diagnoses (e.g., pulmonary embolism) simultaneously.
- Transesophageal echocardiography is a more sensitive test than transthoracic echocardiography, but the latter is better tolerated by unstable patients.
Chest x-ray is not a reliable test to rule in or rule out aortic dissection, but will be abnormal in a majority of patients.

Laboratory Tests

No laboratory tests are helpful in diagnosing aortic dissection.
D-dimer
- A negative d-dimer test has been proposed as a useful test for ruling out dissection.
  - However, data currently do not support the use of d-dimer as the sole modality in diagnosis.[3]
Laboratory abnormalities depend on the vascular sequelae of the dissection.

Imaging

Chest radiography
- Abnormal in 60–90%
- May be normal, particularly in type A dissections[2]
- Widened mediastinum
- Pleural effusion (usually left-sided) may be present.
- Dissections of the descending thoracic aorta: Descending aorta may appear to be wider than the ascending portion.
Dissection can be confirmed by CT, MRI, or ultrasonography (especially transesophageal echocardiography).
CT and MRI
- Highly accurate in identifying the intimal flap and the extent of the dissection
- Each has a sensitivity and specificity > 90%.
- Useful in recognizing intramural hemorrhage and penetrating ulcers
- CT reconstructions can be used to guide surgery.
- MRI can detect blood flow.
  - May be useful in characterizing antegrade vs retrograde dissection
Echocardiography
- Transthoracic echocardiography
  - Imaging technique of choice in unstable patients
  - Overall sensitivity of 60–85%
    - Sensitivity > 80% in diagnosing proximal ascending aortic dissections
    - Less useful for detecting dissection of the arch and descending thoracic aorta
- Transesophageal echocardiography
  - Requires greater skill and patient cooperation
  - Very accurate in identifying dissections of the ascending and descending thoracic aorta, but not the arch
    - 98% sensitivity and ~90% specificity
- Echocardiography provides important information on the presence and severity of:
  - Aortic regurgitation
  - Pericardial effusion
Aortography
- Recommended if results of noninvasive imaging techniques are not definitive
- May be used to:
  - Document diagnosis
  - Identify entry point, intimal flap, and the false and true lumina
  - Establish extent of dissection into the major arteries
- Sensitivity
  - 70% for an intimal flap
  - 56% for the site of intimal tear
  - 87% for false lumen
  - Cannot recognize intramural hemorrhage
Coronary angiography
- May be performed concomitantly with aortography in high-risk patients in evaluation and preparation for surgery

Diagnostic Procedures

EGC
- If no evidence of myocardial ischemia, helpful in distinguishing aortic dissection from myocardial ischemia
- However, ECG changes can mimic those of acute coronary syndrome.

Classification

Anatomic classification
- DeBakey classification
  - Type I: Dissection involves both ascending and descending aorta.
    - Intimal tear occurs in the ascending aorta but involves the descending aorta as well.
  - Type II: Dissection is limited to the ascending aorta.
  - Type III: Dissection is limited to the descending aorta.
- Stanford classification
  - Type A: Dissection involves the ascending aorta (proximal dissection).
    - Independent of site of tear and distal extension
  - Type B: Dissection is limited to the descending aorta (distal dissection).
From a management standpoint, classification into type A or B is more practical and useful because DeBakey types I and II are managed in a similar manner.
Mechanistic classification
- Svensson classification
  - Class 1: classic dissection with true and false lumen
  - Class 2: intramural hematoma or hemorrhage
  - Class 3: subtle dissection without hematoma
  - Class 4: atherosclerotic penetrating ulcer
  - Class 5: iatrogenic or traumatic dissection

Treatment Approach

Medical therapy should be initiated as soon as the diagnosis is considered.
- Patient should be admitted to an intensive care unit for monitoring hemodynamics and urine output.
- Unless hypotension is present, therapy should be aimed at reducing cardiac contractility and systemic arterial pressure, thereby decreasing shear stress on the aorta.
Emergent or urgent surgical correction
- Preferred treatment for ascending aortic dissections (type A) and complicated type B dissections
Medical therapy
- Preferred treatment for uncomplicated and stable distal dissections and intramural hematomas (type B)
Long-term therapy
- For patients with or without surgery
- Control of hypertension
- Reduction of cardiac contractility

Specific Treatments

Short-term medical therapy

Indications
- If aortic dissection is considered in the differential diagnosis, treatment should be begun until the diagnosis is ruled out.
- Uncomplicated and stable distal dissection (type B)
- Goal is to keep systolic blood pressure between 100–120 mmHg to prevent propagation of dissection and rupture.
Preferred regimen: β-adrenergic blocker accompanied by sodium nitroprusside
- β-adrenergic blocker
  - Goal: Administer parenterally to achieve a heart rate of approximately 60 beats/minute.
    - Propranolol, 0.5 mg IV; then 1 mg every 5 min, to a total of 0.15 mg/kg
    - Esmolol, 500 µg/kg IV over 1 min; then 50–200 µg/kg per min
    - Metoprolol, 5 mg IV every 2–5 min for 3 doses; then 2–5 mg/h
    - Labetalol, 20 mg IV over 2 min; then 40–80 mg every 10–15 min, to a maximum of 300 mg
- Sodium nitroprusside
  - Goal: Decrease systolic blood pressure to ≤ 120 mmHg.
    - Dose: 20–400 µg/min IV
Alternative regimen
- Calcium-channel antagonists, verapamil, and diltiazem IV, if nitroprusside or labetalol cannot be used
  - Verapamil, 2.5–10 mg: can repeat with 10 mg after 15–30 min
  - Diltiazem, 0.25 mg/kg IV over 2 min; can repeat with 0.35 mg/kg after 15 min; then 5–15 mg/h IV
- Addition of a parenteral angiotensin-converting enzyme inhibitor, such as enalaprilat, to a β-adrenergic blocker may also be considered.
  - Enalapril, 0.625–1.25 mg IV every 6 h
Contraindicated medications: direct vasodilators (increase hydraulic shear and may propagate dissection)
- Diazoxide
- Hydralazine

Acute surgical therapy

Indications
- Ascending aortic dissections (type A)
- Complicated type B dissections, including those characterized by:
  - Propagation
  - Compromise of major aortic branches
  - Impending rupture
  - Continued pain
Surgical procedure
- Excision of the intimal flap
- Obliteration of the false lumen
- Placement of an interposition graft
- Aortic valve replacement may be necessary in some cases.
A composite valve-graft conduit is used if the aortic valve is disrupted.
Endovascular stent-grafts[4]
- May be used for descending aortic dissections as alternative to open repair
- No prospective randomized trials compare stent-grafts with surgery.
- Indications are still being defined.
- May be evolving role for use combined with open surgery in type A dissections
Other transcatheter techniques, such as fenestration of the intimal flaps and stenting of narrowed branch vessels to increase flow to compromised organs, are also under investigation.

Long-term therapy

Indications
- All patients with dissection, whether initially treated medically or surgically
Goal
- Control hypertension and cardiac contractility
Medications
- Beta blockers plus
  - Metoprolol, 25–100 mg PO bid
  - Atenolol, 25–100 mg/d PO
- Angiotensin-converting enzyme inhibitors
  - Enalapril, 5–40 mg PO once or twice daily
- Calcium antagonists
  - Verapamil, 80–120 mg PO tid; or 120–480 mg/d PO (extended release)
  - Diltiazem, 30–120 mg PO tid or qid; or 180–360 mg/d PO (extended release)

Monitoring

After hospitalization, patients treated both medically and surgically require close outpatient follow-up with monitoring of blood pressure.
- Goal: Maintain systolic blood pressure at ≤ 120 mmHg.
Patients with chronic type B dissection and intramural hematomas should be followed on an outpatient basis every 6–12 months by contrast-enhanced CT or MRI to detect propagation or expansion.

Complications

Redissection
Acute aortic regurgitation
False aneurysm formation or rupture into:
- Left pleural space
- Retroperitoneum
- Pericardium
- Abdominal cavity
Aneurysmal dilatation [5]
- The upper descending thoracic aorta is the major site of late aneurysmal dilation.
- A large upper descending thoracic aorta false lumen diameter on the initial CT portends late aneurysm and adverse outcome warranting early intervention.
End-organ ischemia due to involvement of major branches of the aorta
- MI
- Stroke
- Bowel ischemia
- Renal failure
Hemopericardium
Cardiac tamponade
Superior vena cava syndrome
Horner’s syndrome
Airway compromise
Major causes of perioperative mortality and morbidity
- MI
- Paraplegia
- Renal failure
- Tamponade
- Hemorrhage
- Sepsis

Prognosis

Medically treated type A dissection
- About 33% of patients die within the first 24 hours.
- 50% die within 48 hours.
- The 2-week mortality rate approaches 75%.
Medically treated patients (type B dissection)
- In-hospital mortality rate: 10–20%
Surgically treated patients (type A or complicated type B dissection)
- In-hospital mortality rate: 15–25%
Long-term prognosis for patients with treated dissections is generally good with careful follow-up.
- 10-year survival rate: ~60%
Factors associated with increased in-hospital mortality and poor outcomes[1]
- Age > 70 years
- Shock on presentation
- Branch vessel occlusion resulting in myocardial ischemia or visceral ischemia

Prevention

Treatment of risk factors may be preventative.
- Control hypertension.
- Control hyperlipidemia (atherosclerosis).

ICD-9-CM

441.0_ Dissection of aorta, (anatomic site specified by fifth digit)
441.00 Dissection of aorta, unspecified site