Aortic Dissection

Question 1

Briefly describe the wall of an artery

Answer 1

The wall of an artery consists of the tunica intima (innermost layer), tunica media (middle layer), and tunica adventitia (outermost layer).

Question 2

What is an aortic dissection?

Answer 2

An aortic dissection is a tear in the intimal layer of the aortic wall, causing blood to flow between and splitting apart the tunica intima and media.

Question 3

Differentiate between acute and chronic aortic dissection

Answer 3

It can be defined as acute (when diagnosed ≤14 days) or chronic (when diagnosed >14 days).

Question 4

Who is commonly affected by aortic dissection?

Answer 4

They are more common in men and in patients with connective tissue disorders and have a peak onset between 50-70yrs.

Question 5

Briefly describe the pathophysiology of aortic dissection

Answer 5

Aortic dissections from the initial intimal tear can progress distally, proximally, or in both directions from the point of origin. Anterograde dissections propagate towards the iliac arteries and retrograde dissections propagate towards the aortic valve (at the root of the aorta).

Question 6

What are the 2 classification systems for aortic dissection?

Answer 6

Stanford Classification and DeBakey Classification.

Question 7

Briefly describe Stanford Classification

Answer 7

The Stanford classification divides aortic dissection into two groups, A and B:

• Group A: includes DeBakey Types I and II and involves the ascending aorta and can propagate to the aortic arch and descending aorta; the tear can originate anywhere along this path
• Group B: dissections do not involve the ascending aorta and include DeBakey Type III

Question 8

Briefly describe DeBakey Classification

Answer 8

The DeBakey classification groups aortic dissections anatomically:

• Type I: originates in the ascending aorta and propagates at least to the aortic arch
  
  • They are typically seen in patients under 65yrs and carry the highest mortality,
• Type II: confined to the ascending aorta
  
  • Classically in elderly patients with atherosclerotic disease and hypertension
• Type III: originates distal to the subclavian artery in the descending aorta
  
  • Further subdivided into IIIa which extends distally to the diaphragm and IIIb which extends beyond the diaphragm into the abdominal aorta

Question 9

Explain the various DeBakey Classifications

Answer 9

Type I

• Originates in the ascending aorta and propagates at least to the aortic arch
• They are typically seen in patients under 65yrs and carry the highest mortality

Type II

• Confined to the ascending aorta
• Classically in elderly patients with atherosclerotic disease and hypertension

Type III

• Originates distal to the subclavian artery in the descending aorta
• Further subdivided into IIIa which extends distally to the diaphragm and IIIb which extends beyond the diaphragm into the abdominal aorta

Question 10

What are the risk factors for aortic dissection?

Answer 10

• Hypertension
• Atherosclerotic disease
• Male gender
• Connective tissue disorders (typically Marfan’s syndrome or Ehler’s-Danlos syndrome)
• Biscuspid aortic valve

Question 11

What is shown in the image?

Answer 11

Histopathology of a thoracic aortic dissection, demonstrating the separation of the tunica intima and tunica media.

Question 12

What are the clinical features of aortic dissection?

Answer 12

The characteristic presentation of an aortic dissection is of a tearing chest pain, classically radiating through to the back, yet the diagnosis is often challenging and many be a more subtle presentation.

The most common clinical signs include tachycardia, hypotension, new aortic regurgitation murmur, or signs of end-organ hypoperfusion.

Question 13

What are the signs of end-organ hypoperfusion?

Answer 13

Reduced urine output, paraplegia, lower limb ischaemia, abdominal pain secondary to ischaemia or deteriorating conscious level.

Question 14

Why does hypotension occur following an aortic dissection?

Answer 14

Secondary to hypovolaemia from blood loss into the dissection or cardiogenic from severe aortic regurgitation or pericardial tamponade.

Question 15

What investigations should be ordered for aortic dissection?

Note: laboratory

Answer 15

Baseline blood tests (FBC, U&Es, LFTs, troponin, coagulation) with a crossmatch of at least 4 units, in addition to an arterial blood gas to aid initial assessment. An ECG should also be performed to exclude any cardiac pathology.

Question 16

What investigations should be ordered for aortic dissection?

Answer 16

A computed tomography (CT) angiogram is recommended to diagnose aortic dissection as first line imaging. This will also allow classification, establish the anatomy of the dissection, and assist surgical planning.

A transoesophogeal ECHO can also provide useful information but is operator dependent.

Question 17

What is shown in the image?

Answer 17

CT Chest of Stanford Type B Aortic Dissection.

Question 18

What is the immediate management of aortic dissection?

Answer 18

Urgent initial assessment is required, as for any other critically ill surgical patient.

Start high flow oxygen and gain IV access (x2 large bore cannulas); fluid resuscitation should be done cautiously.

Question 19

Briefly differentiate for the management of Stanford Type A and Type B dissection

Answer 19

Stanford Type A dissections should be managed surgically in the first instance and carry a worse prognosis than Type B dissections. Any uncomplicated Type B dissections can usually be managed medically.

Question 20

What follow up is needed for aortic dissection?

Answer 20

Following initial management, all patients need lifelong antihypertensive therapy and surveillance imaging, due to the high risk of developing further dissection or other complications.

Question 21

How frequent is surveillance imaging following aortic dissection?

Answer 21

Imaging would usually be at 1, 3 and 12 months post-discharge, with further scans at 6-12 month intervals thereafter depending on the size of the aorta.

Question 22

Briefly describe the treatment for Type A dissections

Answer 22

Type A dissections carry a high mortality if left untreated and these cases should be discussed urgently with a cardiac or vascular surgeon. They will most likely require transfer to a cardiothoracic centre.

The surgery involves removal of the ascending aorta (with or without the arch) and replacement with synthetic graft.

Any additional branches of the aortic arch that are involved will require reimplanation into the graft (i.e. brachiocephalic artery, left common carotid artery, left subclavian artery), with long Type A dissections involving the descending and possibly abdominal aorta may require staged procedures.

Question 23

Briefly describe the treatment for Type B dissections

Answer 23

Uncomplicated Type B dissections are best managed medically, with good survival rates. First line treatment is management of hypertension with intravenous beta blockers (labetalol).

In the acute setting, endovascular repair is not recommended due to the risk of retrograde dissection, therefore medical management remains gold standard. Surgical intervention in Type B dissections is only warranted in the presence of certain complications, such as rupture, renal, visceral or limb ischaemia, refectory pain, or uncontrollable hypertension.

Type B dissections can go on to be chronic, with continued leakage into the dissection, even if a stent has been placed. The most common complication of chronic disease is the formation of an aneurysm. These present further surgical problems, with endovascular repair offering a better survival chance.

Question 24

Why are IV beta-blockers used to manage hypetension in aortic dissection?

Answer 24

The aim of this therapy is to rapidly lower the systolic pressure, pulse pressure, and pulse rate to minimise stress of the dissection and limited further propagation.

Question 25

What are the complications of aortic dissection?

Answer 25

Any complications that arise depend on the site and spread of the dissection into the aortic branches, damaging end organs. Consequently, complications that can occur include:

Aortic rupture

• Aortic regurgitation
• Myocardial ischaemia
• Secondary to coronary artery dissection
• Cardiac tamponade
• Stroke or paraplegia
• Secondary to cerebral artery or spinal artery involvement

Question 26

What is the rate of mortality in aortic dissection?

Answer 26

Mortality remains high, with over 20% of cases dying before reaching hospital, however early diagnosis, intervention, and blood pressure control significantly improves prognosis.

Question 27

What differentials should be considered for aortic dissection?

Answer 27

1. Myocardial infarction
2. Pulmonary embolism
3. Pericarditis
4. Musculoskeletal back pain

Question 28

How does aortic dissection and myocardial infarction differ?

Answer 28

Classically crushing and central chest pain, with signs of cardiac ischaemia on ECG and / or raised serum troponin levels.

Question 29

How does aortic dissection and pulmonary embolism differ?

Answer 29

Dyspnoea will be a prominent feature and an ABG will demonstrate hypoxia, confirm with CTPA or V/Q scan.

Question 30

How does aortic dissection and pericarditis differ?

Answer 30

Classically pleuritic chest pain, with the ECG showing diffuse ST elevation, as well as potential pericardial rub on auscultation.

Question 31

How does aortic dissection and MSK pain differ?

Answer 31

The patient will not present with systemic signs of shock and will be tender to palpation of the chest wall or paraspinal muscles.