Table of Contents
- Definition and Background of Aortic Dissection
- Epidemiology of Aortic Dissection
- Etiology of Aortic Dissection
- Classification of Aortic Dissection
- Pathophysiology of Aortic Dissection
- Pathology of Aortic Dissection
- Symptoms of Aortic Dissection
- Diagnosis of Aortic Dissection
- Treatment of Aortic Dissection
- Prognosis of Aortic Dissection
- Popular Exam Questions on Aortic Dissection
Definition and Background of Aortic Dissection
What is an aortic dissection?
Aortic dissection occurs when the inner coat (tunica intima) of the aortic wall splits, causing blood to enter layers of the wall to form a channel of blood. The pressure of this causes the layers to be forced apart and causes severe pain, characteristically known as a tearing pain. This medical emergency is very serious as it can partially occlude and reduce blood flow to the rest of the body causing vital organs to be starved of blood and nutrients. If severe, the aorta can completely rupture and cause rapid death. There are risk factors associated with aortic dissection, such as hypertension, and there are also genetic diseases that can markedly increase the chances of occurrence.
Epidemiology of Aortic Dissection
Who is affected by aortic dissection?
Aortic dissection is a rare condition which occurs at a rate of 2-3.5 per 100,000 people every year. It is more common in men than women as 65 % of all dissections occur in males. There is a link with pregnant females, as this accounts for half of all dissections in women under 40 (rare). Peak incidence is around 50 – 65 years of age and nearly all occur between 40 – 70 years.
Dissections that occur around 30/40 years of age are usually associated with genetic disease / connective tissue disease.
Men aged 40 to 60 with hypertension make up 90 % of cases. It is more common in Afro-caribbean people than caucasians. Asians have a lower occurrence compared to caucasians.
Etiology of Aortic Dissection
Causes of aortic dissection
- 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’s syndrome (more likely to be proximal dissections), Ehler-Danlos syndrome
- Turner’s syndrome (causes aortic root dilatation)
- Blunt chest trauma (e.g car accidents) or iatrogenic trauma (during catheterisation or intra-aortic balloon pump procedures)
- Bicupsid aortic valve (congenital) – increases chance of ascending aortic dissection
- Syphilis (tertiary stage)
- Cardiac surgery – especially aortic valve replacement as aortic regurgitation can cause dilatation and aortic wall weakening.
|Modifiable Risk Factors||Unmodifiable Risk Factors|
|Hypertension (can be unmodifiable if genetic or secondary)||Age|
|Atherosclerosis – lipid levels||Sex – Male|
|Iatrogenesis||Genetic Conditions (e.g. Marfan’s, Ehlers-Danlos)|
|Bicuspid aortic valve|
|Coarctation of the aorta|
|Arteritis and syphilis induced swelling of vessels|
Classification of Aortic Dissection
Stanford and DeBakey systems
There are several systems of classification for aortic dissection based on anatomy or duration of onset of symptoms.
The Stanford system is the most commonly used one:
|Type A 70 – 75 %||Ascending aorta +/- aortic arch, possibly descending aorta. Can involve the aortic valve||Tear can originate in any 3 (rarely originates in the descending aorta)Includes DeBakey 1 + 2Requires primary surgical treatment|
|Type B 25 – 30 %||Descending aorta or the aorta (distal to the left subclavian artery) without involvement of the ascending aorta||Includes DeBakey 3Mortality is not improved by surgery unless it is complicated – therefore surgery is not the primary treatment|
In contrast, the DeBakey system is based on anatomy:
|Type 1 60 %||Origin – ascending aorta, extends to aortic arch and often beyond. Most lethal of often seen in patients <65.|
|Type 2 10 – 15 %||Origin – ascending aorta and is confined here|
|Type 3 25 – 30 %||Origin – descending aorta – rarely goes proximally but commonly goes distally. Elderly with hypertension and atherosclerosis.|
Pathophysiology of Aortic Dissection
Conditions observed with aortic dissection
In aortic dissection, blood enters the intima and the media layers. The high pressure of blood tears the media apart in a laminated plane. The plane is usually between the inner 2/3rd and the outer 1/3rd. The dissection can extend proximally and/or distally for variable distances.
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 of course causes huge internal bleeding or cardiac tamponade if the dissection extends through the adventitia but into the pericardial sac, forming a hemocardium. Both scenarios are severely life-threatening and can lead rapidly to death.
It is possible for the dissection to enter the aortic walls and then recanalize the lumen of the aorta through another second distal intimal tear which extends medially rather than laterally. This condition is less serious for patients as there is a pathway for the blood to leave preventing a serious build up of pressure. Eventually, this can lead to a chronic dissection and the channel can become covered in endothelium leading to a double-barrel aorta (there are now two vascular channels within the aorta). Retroperitoneal and pericardial ruptures are possible if the pressure build up is great enough.
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 as discussed above, but generally, 65 % originate in the ascending aorta, 10 % in the aortic arch and 20 % occur in the descending thoracic aorta (distal to the ligamentum arteriosum).
The reason the intima occurs is unknown. It can occur as a result of high blood pressure, sporadically or due to genetic connective tissue diseases such as Marfan’s syndrome. In Marfan’s the key issue is that the collagen and elastin within the media are degenerative, unstructured and dysfunctional – cystic medial necrosis (as discussed below).
In approximately 10 % of cases, there is no evidence that an intimal tear was present. These dissections may be caused by bleeding within the medial of the vessel causing a secondary aortic dissection – this is still treated in the same way.
Genetic disease implications
Marfan’s syndrome is a connective tissue disorder which involves the misfolding of fibrillin-1. This is a protein that forms elastic tissue and has roles in signalling. One such role includes binding to TGF-beta; the mutated fibrillin-1 fails to do this and this causes an accumulation of TGF-beta in various tissues including the aorta, causing weakened tissue with an abnormal structure and function.
Ehlers-Danlos syndrome is where a genetic problem causing incorrect production and processing of collagen, an essential protein involved in structure of tissues. This can lead to a weakened vessel walls which can quickly become aneurysmal.
Pathology of Aortic Dissection
Lesions associated with aortic dissection
The most commonly identified lesion within the aortic wall is cystic medial degeneration – decrease in smooth muscle, necrosis, fragmentation of elastic tissue and deposition of proteoglycan-rich extracellular matrix. Cystic medial degeneration is usually related to genetic disease such as Marfan’s syndrome. There may be further evidence of atherosclerosis, abnormal connective tissue structure in genetic conditions. Inflammation is absent. Dissection can also occur when no identifiable histological lesions are present and can be spontaneous.
Symptoms of Aortic Dissection
Chest pain and other indications for aortic dissection
Thoracic aortic dissection should be considered in all patients with chest pain. This pain usually has the following characteristics:
- Site: Chest pain; depends on where the dissection arises (can mimic myocardial infarction pain). This pain is due to the interruption of blood flow to the coronary arteries causing ischaemia (usually when arch or root is affected). Pain is usually more sudden and is maximal at onset, unlike MI’s. Painless in 10 % of patients.
- Onset: sudden
- Character: excruciating tearing/ripping pain (tearing pain between the shoulder blades is usually associated with descending aortic dissection).
- Radiation: to the back and/or in-between the shoulders. Can radiate to the neck or jaw (usually occurs with arch dissection which spreads into the branches of the aorta).
- Severity: usually excruciating (can be mild in some cases)
The following neurological symptoms can be the presenting complaint (20 %):
- Syncope (hypovolemia, arrhythmia, increased vagal tone)
- Altered mental status
- Stroke (CVA) – hemiparesis or hemiplegia with hemianesthesia
- Change in sensation (tingling, paresthesia, pain) and motor function (weakness) can occur if peripheral nerves are affected by the lack of blood supply.
Additionally, other types of symptoms may occur alongside aortic dissection:
- Cardiovascular symptoms: There may be acute severe aortic valve compromise leading to secondary congestive heart failure. This leads to orthopnoea and dyspnoea.
- Hypertensive: underlying hypertension or increase in circulating catecholamines.
- Hypotensive: poor prognostic sign as may be the result of cardiac tamponade, hypovolemia or increase vagal tone.
- Symptoms of esophageal compression: dysphagia.
- Abdominal pain if spread to abdominal aorta.
- Flank pain if renal artery is involved.
- Symptoms of systemic disease(s): Patients may have established disease(s) related to the aortic aneurysm and could therefore have symptoms of: peripheral vascular disease, infection, trauma, Marfan’s syndrome or Ehler-Danlos syndrome.
Signs for aortic dissection
The following list comprises the most common symptoms of aortic dissection:
- Blood pressure : difference of >20 mmHg between left and right arms (20 % don’t have this).
- Aortic regurgitation: bounding (collapsing/waterhammer) pulse, wide pulse pressure, murmurs (diastolic).
- Signs of congestive heart failure secondary to acute severe aortic valve dysfunction leading to orthopnoea, dyspnoea, elevated JVP and bibasal crackles.
- Possibly unconscious.
- Cardiac tamponade: distension of jugular veins, hypotension, pulsus paradoxus, Kussmaul’s sign
- SVC obstruction can lead to SVC syndrome.
- Signs of stroke – e.g. body leaning to one side due to hemiparesis.
- Patient in shock; cold, clammy, pale, tachycardia, tachypnoea.
- Horner’s syndrome may be present due to compression.
- New diastolic murmur and/or asymmetrical pulses.
- Pulse: carotid, brachial and femoral may be abnormal.
- Bruits: may be present initially or may develop.
- Signs of hemothorax may be present if the dissection ruptures into the pleura – rapid shallow breaths, sharp pleuritic pain.
- Anxiety, sense of impending doom.
- Acute arterial insufficiency in the lower or upper limbs, as indicated by: weak pulses, pallor, low body temperature, loss of sensation – paraesthesia, paralysis
- Marfan’s syndrome signs – e.g. high arched palate
- Ehlers-Danlos syndrome signs
- Trauma signs e.g. usually blunt trauma
Risks inherent in aortic dissection
Aortic dissection might cause the following complications:
- Hypotension and shock (hypovolemic): eventually death by exsanguination (blood loss)
- Permanent disability from stroke (CVA)
- Acute aortic regurgitation: proximal dissection spreading to the sinus of valsalva and aortic root.
- Pulmonary edema: acute aortic valve regurgitation
- Pericardial tamponade: due to blood in the pericardial sac (hemopericardium)
- Myocardial ischaemia – reduction in blood flow to the coronary arteries
- Aortic insufficiency
- Myocardial infarction
- Global ischaemia e.g. mesenteric, bowel, renal, spinal cord, visceral ischaemia/infarction
- Compression: oesophagus, SVC, ganglia (sympathetic chain causing Horner’s syndrome), airway, left recurrent laryngeal nerve (hoarseness and vocal cord paralysis).
- Aortic aneurysm
Diagnosis of Aortic Dissection
Methods of detecting aortic dissection
Diagnosis of aortic dissection needs to be rapid and accurate. The following procedures are recommended:
- Physical examination: signs as stated above.
- History: In stable patients, a detailed history should be taken to assess risk factors, hypertension status, risk of rupture, symptom duration and onset and any family history or genetic conditions.
Investigations are used to diagnose and reveal the site of the intimal tear and extent of dissection:
Gold standard for detection and assessment. Sensitivity and specificity of 98 %
- Can create a 3D reconstruction and can determine the intimal tear location (unlike on CT scans) and extent of the dissection.
- No iodinated contrast needed
- Quantifies the level of aortic insufficiency
- May only be available at larger hospitals in well-developed countries. Takes longer than CT scans and therefore may be less useful.
- CT Scan
Non-invasive, rapid and accurate test that can give a 3D view of the aorta – especially useful for surgical interventions
- Injected iodinated contrast medium used
- Very sensitive and specific investigation
- Unable to diagnose site of intimal tear
- Chest X-ray
- Pleural effusions may be visible
- Calcium sign – the calcified intima is separated from the outer aortic soft tissue border by 1 cm (rare)
- Obliteration of the aortic knob
- Catheterisation of the aorta (via the femoral artery) and injection of contrast whilst x-rays are taken of the aorta. Useful for determining luminal size and to determine and aortic dissections that may be present
- Blood test – <500 ng/ml may rule out aortic dissection in low risk patients, within 24 hours. It is not specific as D-Dimer can be raised for other reasons, therefore, if suspicious, confirm with imaging.
- Cannot be used for diagnosis on its own
- Transoesophageal echocardiogram
- High sensitivity and specificity
- Fast, non-invasive and fairly inexpensive
- Can determine if valves or ostia of the coronary arteries are involved
- Does not provide a full view, hence MRI is recommended
- The aorta is catheterised and contrast is injected.
- X-rays are taken to determine flow within the aorta.
- Standard blood tests – to confirm diagnosis and rule out differential diagnoses
Consider aortic dissection with all chest pain presentations:
|Heart||Myocarditis, aortic regurgitation, aortic stenosis, cardiogenic shock, myocardial infarction, aortic aneurysm|
|MSK||Mechanical back pain, muscular pain|
|Respiratory||Pleural effusion, pulmonary embolism|
Treatment of Aortic Dissection
Possible therapy for aortic dissection
|Acute Stanford Type A (DeBakey 1+2)||Surgery > Medical|
|Acute Stanford Type B (DeBakey 3)||Medical > Surgical|
If the patient presents with a chronic aortic dissections (present for >2 weeks) that they have survived, the treatment varies as the mortality is much higher for acute aortic dissections (66 % cases).
Surgical treatment may be indicated for serious acute dissections (e.g. type A). The surgery is high risk due to its proximity to the heart and the importance of the aorta. The surgery aims to remove the damaged aorta section and repair the false lumen to prevent entry of blood. The intimal tear can be removed. The surgery can be carried out via open surgery (more common) or endovascularly. The surgery can replace the damaged aorta with a tube graft and/or repair the damaged aortic valve if it is implicated in the aortic dissection.
Any patient who presents with aortic dissection needs immediate blood pressure control. The target is 60 – 75 mmHG mean arterial blood pressure. This is to be managed long term which may involve medication and therapy to control emotional and psychological factors.
- Beta blockers – first line treatment.
- Vasodilators – if beta blockers do not reduce the blood pressure enough.
- Calcium channel blockers – if beta blockers are contraindicated (e.g asthma)
Prognosis of Aortic Dissection
40 % of all patients die suddenly with acute aortic dissection. Of the remaining 60 %, 1 % of these die every hour; this highlights the importance of rapid diagnosis and referral for surgical repair (or medical if indicated). The surgery itself is extremely high risk with a mortality of 5-20%.
Ascending aorta dissections have a much worse prognosis in comparison to thoracic aortic dissections.
There are risk factors which affect the prognosis post-operatively: increased pre-operative evaluation time, older age, leakage of aneurysm, cardiac tamponade, pre-existing heart pathology (MI, Coronary artery disease), previous stroke, shock, kidney failure history (acute/chronic).
Increased screening takes place for those with a family history / those individuals suffering from genetic condition known to increase the chance of developing aortic dissection (e.g. Marfan and Ehler-Danlos syndromes).
Popular Exam Questions on Aortic Dissection
The answers can be found below the references.
1. The most common type of aortic dissection is…
- …Stanford Type A.
- …Stanford Type B.
2. Which of the radiological investigations, (assuming all are available at the hospital) is the most useful for diagnosing and managing aortic dissection?
- CT Scan
- MRI Scan
3. In aortic dissection, what is the strand of tissue known as, that splits off but remains in the lumen?
- Intimal tear
- Intimal flap
- Medial slice
- Medial tear
- Adventitial flap