Lecturio Medical Knowledge Essentials – Aortic Dissection

Authors: Ahmed Elsherif ¹ ; Michelle Wyatt ²
Peer Reviewers: Stanley Oiseth ³ ; Joseph Alpert ⁴
Affiliations: ¹ Suez Canal University; ² Medical Editor at Lecturio; ³ Chief Medical Editor at Lecturio; ⁴ Tucson University, Arizona

Aortic dissection is an emergency that occurs due to shearing stress from pulsatile pressure causing a tear in the tunica intima of the aortic wall. This tear, often associated with uncontrolled hypertension, allows blood to flow into the medial layer, thus creating a false lumen.[1] Patients often present with acute, severe chest or back pain, described as “tearing.” Complications arise due to partial occlusion of vital branches of the aorta with reduced blood flow to the brain, visceral organs, and extremities. Computed tomography is the diagnostic imaging modality of choice. All type A or proximal dissections (ascending aorta) are surgical emergencies due to the risk of imminent rupture. Type B or distal dissections (descending aorta) can be managed medically with beta-blockers and calcium channel blockers. If there is evidence of decreased perfusion to visceral organs or extremities, aneurysm dilation > 5 cm, retrograde extension into the ascending aorta, or intractable pain, then evaluation for endovascular or open repair is required.[2, 3]

For further review of this topic, including links to lectures by specialists in the field, follow this link: https://www.lecturio.com/concepts/aortic-dissection/

This article is not intended to substitute for professional medical advice and should not be relied on as health or personal advice. Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition.

Definition

An aortic dissection occurs due to longitudinal cleavage of the medial layer of the vessel wall, creating a false lumen in the aorta. It is a surgical emergency as the dissection causes reduced blood flow to vital organs. In severe cases, the aorta can rupture and be fatal.

Epidemiology

Aortic dissection (AD) is an infrequent occurrence, with new cases reported at 2–3.5 per 100,000 people every year. It is more common in men (65%) than women and is often associated with hypertension.
The age of presentation of AD depends on underlying risk factors. Age, male sex, and hypertension confer the most significant risks in adults over 40, but genetic connective tissue diseases increase the risk of AD in younger patients. It is more common in the African American population than whites, similar to hypertension, and Asians have the lowest incidence. Dissections in younger individuals ages 30–40 are usually associated with genetic or connective tissue diseases such as Marfan syndrome.[4,5]

Etiology

Acquired Causes — Risk Factors [6]

• Hypertension 
• Atherosclerosis
• Blunt chest trauma (e.g., motor vehicle accidents, though they are usually deceleration injuries that more commonly cause a complete aortic transection or iatrogenic trauma (during catheterization or intra-aortic balloon pump counterpulsation)
• Pregnancy, especially in the third trimester and in the postpartum period [7,8]
• Syphilis (tertiary stage) with aortic involvement due to vasculitis
• Amphetamines and cocaine use
• Cardiac surgery—especially aortic valve replacement, since aortic regurgitation can cause dilatation and aortic wall weakening [10]

Congenital Causes

• Genetic disease/connective tissue abnormalities that affect the aorta; affects the structure and function of connective tissue/proteins (e.g., collagen and elastin) in the walls of the aorta — Marfan syndrome (more likely to be proximal dissections), Ehlers-Danlos syndrome [9]
• Turner syndrome (due to aortic root dilatation)
• Bicuspid aortic valve increases the chance of ascending aortic dissection.
• Coarctation of the aorta

High-yield facts:

• 70 % or more of patients with AD have hypertension. 
• Hypertension is more common in those with distal (type B) dissection compared to type A. 

Classification

There are several systems of classification for aortic dissection based on anatomy or duration of onset of symptoms.

Two classifications are used for aortic dissections; the Stanford classification is used more often. Both the DeBakey classification and the Stanford classification are used to separate aortic dissections into those that need surgical repair and those that usually require only medical management. DeBakey Type I involves the ascending aorta, arch, and descending thoracic aorta and may progress to involve the abdominal aorta); DeBakey Type II is limited to the ascending aorta; DeBakey Type IIIa involves the descending thoracic aorta distal to the left subclavian artery and proximal to the celiac artery; DeBakey Type IIIb involves the thoracic and abdominal aorta distal to the left subclavian artery. In the Stanford classification, Type A involves the ascending aorta and may progress to involve the arch and thoracoabdominal aorta. Type B involves the descending thoracic or thoracoabdominal aorta distal to the left subclavian artery without the involvement of the ascending aorta. The treatment of type A dissections is surgical unless the patient would not survive the surgery. Type B dissections can usually be managed medically, but surgery or endovascular intervention may be used if there are complications or progressive symptoms. Other classifications of aortic dissections are also used to improve specificity and reporting standards [10].
Image by Lecturio.

Stanford Classification

Mnemonic:
Stanford A = affects ascending aorta
Stanford B = begins beyond brachiocephalic vessels

The Stanford classification is the most commonly used in aortic dissection.

DeBakey system

In contrast, the DeBakey system is based on anatomy:

Type 1 60%	Origin — ascending aorta extends to the aortic arch and often beyond. Most lethal and often seen in patients < age 65.	Image: “DeBakey Type 1” by JHeuser. License: CC BY-SA 3.0
Type 2 30%–35%	Origin — ascending aorta and is confined here.	Image: “DeBakey Type 2” by JHeuser. License: CC BY-SA 3.0
Type 3 10%–15%	Origin — descending aorta — rarely goes proximally but commonly goes distally. Elderly with hypertension and atherosclerosis.	Image: “DeBakey Type 3” by JHeuser. License: CC BY-SA 3.0

Pathophysiology

In patients with AD, blood enters the intima from the media layers. The high pressure exerted by blood tears the media apart in a laminated plane. The plane is usually between the inner 2/3rds and the outer 1/3rd. The dissection can extend proximally or distally for variable distances and establishes a connection between the media and intima through a false lumen. [13]

Most dissections originate in the ascending aorta, usually within 10 cm of the aortic valve. These tears are commonly 1–5 cm long and are transverse or oblique in orientation, with rough edges.

• Antegrade dissection — spreads towards the iliac bifurcation and sometimes all the way down to the iliac and femoral arteries
• Retrograde dissection — spreads towards the aortic root and heart

Sometimes, the dissection can spread through the intima, media, and adventitia causing external rupture. This results in huge internal bleeding or cardiac tamponade if the dissection extends through the adventitia but into the pericardial sac, forming a hemopericardium. Both scenarios are life-threatening and can rapidly lead to death.

When the blood enters the intima and tears through the media, it creates a false lumen. The true lumen is the natural physiological lumen of the vessel. In between both of these lumens is a layer of intima which is known as the intimal flap. As stated above, the false lumen may recanalize into the true lumen.

There are different types of aortic dissection. The majority originate in the ascending aorta, about 10% in the aortic arch, and 15% in the descending thoracic aorta (distal to the ligamentum arteriosum).[12]

The reason an intimal tear occurs is unknown. It can occur due to intimal ischemia from increased shear forces due to hypertension or genetic connective tissue diseases such as Marfan syndrome. In patients with Marfan syndrome, the collagen and elastin within the media are degenerative, unstructured, and dysfunctional—causing cystic medial necrosis.

In approximately 10% of cases, there is no evidence of an intimal tear. These dissections may be caused by bleeding within the medial layer of the vessel resulting in secondary aortic dissection.

This drawing illustrates how an intimal tear leads to bleeding into the media, creating a false lumen. Image: “Scheme of aortic dissection” by JHeuser. License: CC BY-SA 3.0

Genetic Disease Implications

• Marfan syndrome is a connective tissue disorder that involves the misfolding of fibrillin-1. This is a protein that forms elastic tissue and has roles in signaling. One such role includes binding to TGF-beta; inappropriate functioning of the mutated fibrillin-1 causes an accumulation of TGF-beta in various tissues, including the aorta, resulting in weakened tissue with an abnormal structure and function. 
• Ehlers-Danlos syndrome is a genetic condition characterized by insufficient production and processing of collagen (an essential protein involved in the structure of tissues). This can lead to weakened vessel walls that can develop an aneurysm. [9]

Pathology

The most commonly identified lesion within the aortic wall is cystic medial degeneration, manifesting as decreased smooth muscle, necrosis, elastic tissue fragmentation, and proteoglycan-rich extracellular matrix deposition. Cystic medial degeneration is usually related to genetic diseases like Marfan syndrome. There may be further evidence of atherosclerosis and abnormal connective tissue structure in genetic conditions. Inflammation is absent. Dissection can also be spontaneous and occur when no identifiable histologic lesions are present. [11]

This is a histopathological photo of a dissecting thoracic aortic aneurysm in a patient without evidence of Marfan trait. The damaged aorta was surgically removed and replaced by an artificial vessel. Image: “Victoria blue & HE stain.” by KGH. License: CC BY-SA 3.0

Clinical Features

Symptoms

The diagnosis of thoracic aortic dissection should be considered in all patients with chest pain. This pain usually has the following characteristics: [12,14]

• Location: chest pain depends on the site of the dissection and can mimic the pain of myocardial infarction). Chest pain occurs due to the interruption of blood flow to the coronary arteries, causing ischemia (usually when the arch or root are affected). Pain is usually more sudden and severe at the onset when compared to infarctions. Dissection is painless in about 10% of patients.
• Onset: sudden
• Character: severe tearing/ripping pain (tearing pain between the shoulder blades is usually associated with a descending aortic dissection).
• Radiation: to the upper back. Pain can radiate to the neck or jaw (usually with arch dissection spreading to the branches of the aorta).
• Severity: usually excruciating; can be mild in some cases.

Neurological symptoms are the presenting complaint in 20% of cases:

• Syncope (hypovolemia, arrhythmia, increased vagal tone)
• Altered mental status
• Stroke (CVA)—hemiparesis or hemiplegia with hemianesthesia
• Sensory paresthesias and motor weakness can occur if peripheral nerves are affected by the lack of blood supply.
• Hoarseness due to compression of the laryngeal nerve

Additionally, other types of symptoms may occur with AD:

• Cardiovascular symptoms due to acute severe aortic valve compromise leading to secondary congestive left heart failure with orthopnea and dyspnea
• Elevated blood pressure due to underlying hypertension or an increase in circulating catecholamines
• Hypotension, a poor prognostic sign, may result from cardiac tamponade, hypovolemia, or increased vagal tone.
• Dysphagia due to esophageal compression
• Abdominal pain if the dissection extends to the abdominal aorta
• Flank pain m if the renal arteries are involved
• Symptoms of systemic diseases in patients with associated connective tissue disease or peripheral vascular disease

Signs

This list comprises the most common signs of aortic dissection: [12,14]

• Blood pressure that is unequal in both arms, usually with a difference of > 20 mm Hg between left and right arms (may be normal in 20%) due to dissection obstructing the branches of the aorta
• Aortic regurgitation is characterized by bounding (collapsing/water hammer) pulse, wide pulse pressure, diastolic murmur
• Signs of congestive heart failure secondary to acute severe aortic valve dysfunction leading to orthopnea, dyspnea, elevated JVP, and bibasilar crackles
• Possible loss of consciousness
• Cardiac tamponade, characterized by distention of jugular veins, hypotension, pulsus paradoxus, Kussmaul sign
• Superior vena cava (SVC) obstruction can cause SVC syndrome in rare cases
• Signs of stroke—e.g., body leaning to one side due to hemiparesis
• Shock; cold, clammy, pale, tachycardic, tachypneic
• Horner syndrome if there is compression of the cervical sympathetic chain
• Decreased sensation to touch in the extremities due to peripheral ischemia
• Signs of hemothorax if the dissection ruptures into the pleura; rapid shallow breathing, sharp pleuritic pain
• Acute arterial insufficiency in the lower or upper limbs, as indicated by weak pulses, pallor, loss of sensation, or motor weakness
• Signs of connective tissue disorders such as Marfan and Ehlers-Danlos syndromes; hypermobility, tall height, long arm span

Diagnosis

Diagnosis of aortic dissection needs to be rapid and accurate. As previously explained, the diagnosis should be suspected from the history and physical examination.

Imaging

When there is a high clinical suspicion of aortic dissection, imaging studies must be done emergently to confirm or exclude the diagnosis.[14] Each has its advantages and disadvantages, and selection depends on test availability and the patient’s presentation.

Chest X-ray

• Initial imaging shows mediastinal widening; pleural effusions may be visible.
• Calcium sign—the calcified intima is separated from the outer aortic soft tissue border by one cm (rare)
• Obliteration of the aortic knob

This chest X-ray shows mediastinal widening (line labeled as 1) and a prominent aortic knob (line labeled as 2) in a patient with a Stanford type A aortic dissection. Small pleural effusions are also noted. Image: “Chest x-ray of aortic dissection type Stanford A” by JHeuser. License: CC BY-SA 3.0

Transesophageal echocardiogram (TEE)

• Most rapid means of providing sufficient detail to proceed directly to the operating room [15]
• Recommended for hemodynamically unstable patients but requires procedural sedation, which may have adverse effects
• Fast, minimally invasive, and can be used in unstable patients or those with renal insufficiency or contrast allergy 
• Can determine if valves or ostia of the coronary arteries are involved
• Can detect entry tear sites, false lumen flow/thrombus, and pericardial effusions
• Does not provide a complete view; MRI is recommended if available and the patient is stable enough

CT Scan

• Noninvasive, rapid, and accurate test that can give a 3D view of the aorta—especially useful for surgical interventions [16,17]
• Most common initial choice in the emergency department (in stable patients) 
• Diagnosis of AD by CT requires the identification of 2 distinct lumens; the intimal flap may or may not be seen.
• Injected iodinated contrast medium is used
• Highly sensitive and specific [16,17]
  

  The initial presenting signs and symptoms of acute AD are diverse, and early diagnosis can be challenging. This CT is from a 61-year-old man who presented by ambulance to the emergency department with an atypical history of transient loss of consciousness and a suspected seizure. Loss of consciousness was again seen in the emergency department with an ECG monitor recording transient cardiac asystole followed by spontaneous recovery of sinus rhythm. His chest X-ray revealed a widened mediastinum, and a CT (above) demonstrated a Stanford type A aortic dissection from the aortic root. (A) Axial view; (B) sagittal view. [18] Arrows indicate the intimal flap. Image: Arrows indicate intimal flap, by Medicine. License: CC BY 4.0

MR angiogram

• If immediately available and the patient is hemodynamically stable, MRI is the most useful for diagnosing and managing aortic dissection.[19]
• Highly sensitive and specific
• May be done with or without contrast, depending on the situation
• Creates a 3D reconstruction to determine the location of the intimal tear (unlike CT scans) and the extent of the dissection
• Noninvasive
• Takes longer than CT scans; therefore may be less practical
  

  Magnetic resonance tomography in a patient with an aortic dissection; (1) shows the descending aorta with dissection noted; (2) shows the aortic arch. Note both the true and false lumens visualized. Image: “MRT scan of aortic dissection” by Dr. Lars Grenacher. License: CC BY-SA 3.0

Differential Diagnoses

Myocarditis, myocardial infarction, aortic aneurysmal rupture, and mechanical chest pain (e.g., costochondritis) are other conditions in the differential diagnosis of aortic dissection.

Treatment

Type A (DeBakey 1+2) acute ascending aortic dissection is treated emergently with open surgery, less often by endovascular stent-grafting if there are major comorbidities, and a hybrid approach has been used (surgical repair of the ascending aorta, and endovascular stent-graft for the descending aorta). As soon as acute type A aortic dissection is diagnosed, immediate cardiac surgical consultation is required. If experienced cardiac surgical services are not available, the patient should be promptly transferred for definitive care. [20,22]

Type B (DeBakey3) descending aortic dissection is initially treated by beta-blockers, vasodilators, or calcium channel blockers. Surgical or thoracic endovascular repair are indicated if there are complications (occlusion of a major branch, severe hypertension, chest pain, propagation of the dissection aneurysmal expansion, expanding hematoma, or rupture). Complicated type B dissections can be treated with thoracic endovascular aortic repair, now considered the gold standard intervention in this situation. [21]

Early Treatment 

IV beta blockers are the first-line early treatment of AD to decrease the heart rate to a goal of 60 bpm. IV labetalol, esmolol, and propranolol are used in this setting. The next step is to control hypertension if not achieved with beta blockers alone; add-on therapy with nitroprusside (for systolic BP > 120 mm Hg) or calcium channel blockers can be used if beta blockers are not tolerated.

Note:

Initial treatment should be beta-blockers before vasodilators to avoid reflex tachycardia.

Note:

Beta-blockers decrease the heart rate, reducing shearing forces with the aorta.

Surgery

Aortic dissection involving the ascending aorta is a surgical emergency. The surgery involves excision of the intimal tear, obliteration of the proximal entry point into the false lumen, reconstitution of the aorta with a synthetic graft, and repair or replacement of the aortic valve.

Complications

Aortic dissection may cause these complications:[22]

• Hypotension, hypovolemic shock, and death due to  exsanguination (severe blood loss)
• Permanent disability from stroke (CVA)
• Acute aortic regurgitation leading to proximal dissection spreading to the sinus of Valsalva and the aortic root
• Pulmonary edema related to acute aortic valve regurgitation
• Pericardial tamponade due to blood in the pericardial sac (hemopericardium)
• Myocardial ischemia due to reduction in blood flow to the coronary arteries
• Aortic insufficiency
• Myocardial infarction (MI)
• Global ischemia (e.g., mesenteric/intestinal, renal, spinal cord, other sites of visceral ischemia/infarction)
• Compression of some anatomical parts such as the esophagus, SVC, ganglia (sympathetic chain causing Horner syndrome), airway, and left recurrent laryngeal nerve (hoarseness and vocal cord paralysis).
• Aortic aneurysm

Prognosis

Acute aortic dissection has a high mortality rate, about 1% per hour for type A dissection if untreated, which highlights the importance of rapid diagnosis and referral for surgical repair or medical treatment if indicated. In-hospital mortality, including operative deaths, was 22% in a review of 487 patients. [20] Type A aortic dissections have a much worse prognosis than descending thoracic aortic dissections.

In a meta-analysis comparing thoracic endovascular repair versus medical management for acute uncomplicated type B aortic dissection, no difference was seen in short-term (1 month) and mid-term (2.5 years) mortality.[23] Patients with complicated type B dissections have a higher mortality rate than uncomplicated, and thoracic endovascular aortic repair is considered the gold standard intervention in this situation.[24]

Medically treated patients must be closely followed with serial imaging (MR or CT) every 6 months for the first 2 years, then annually.

Risk factors that affect the prognosis postoperatively:

• Increased preoperative evaluation time
• Older age
• Leakage of an aneurysm
• Cardiac tamponade
• Pre-existing cardiac pathology (MI, coronary artery disease)
• Previous stroke
• Shock
• Kidney failure (acute or chronic)

Screening

High-risk individuals with a family history of collagen-vascular disease or AD should be screened with imaging, especially if they have hypertension.

Review Questions

1. The most common type of aortic dissection is…?
   1. …Stanford Type A.
   2. …Stanford Type B.
2. What imaging study is the most useful for diagnosing and managing aortic dissection in a hemodynamically stable patient?
   1. CT Scan
   2. X-ray
   3. Aortogram
   4. MRA
   5. Echocardiogram
3. What strand of tissue splits off in an aortic dissection but remains in the lumen?
   1. Intimal tear
   2. Intimal flap
   3. Medial slice
   4. Medial tear
   5. Adventitial flap

Answers: 1A, 2D, 3B