Aortic Dissection

Key facts:

Authors: Christopher Todd, Colette Marshall, Dawn Adamson, Christoph A. Nienaber
Top Tip: Imaging-based classification of dissection forms the basis of treatment and prognosis

Key Differential Diagnoses

• Any sudden onset of chest and/or back pain
  • Cardiac (ACS, including acute MI)
  • Respiratory (massive PE, pneumothorax)
  • GI (peptic ulcer, pancreatitis)
• Neurovascular (e.g. stroke)
  Note: Neurovascular symptoms can also herald proximal aortic dissection 

Key Investigations

• ECG within 10 mins of arrival
• CXR (widened mediastinum; and to exclude other diagnoses)
• CT (or MR) angiogram
• Transthoracic ECHO (if on-site cardiology available) to assess aortic root and valve in cases where type A is suspected (also to screen for pericardial effusion, aortic regurgitation)
• FBC, U+E, LFT, Bone, Glucose, G&S
• CRP, ABG
• D-dimer (raised)
• Cardiac Troponin, if the patient presents > 6h after the onset of pain; may be raised if MI is diagnosis, or complication

 Key Treatments

• Resuscitate ABCDE
• IV MORPHINE 2.5-5 mg and IV METOCLOPRAMIDE 10mg
• High flow OXYGEN
• NBM
• If hypertension severe, control SBP to 100-120mmHg:
  • IV LABETOLOL (250mg/250mls 5% dextrose) at 2-8 mg/min, increasing every 15 mins to a maximum dose of 200mg; or
  • IV SODIUM NITROPRUSSIDE (50mg/500 ml 5% GLUCOSE) at 10 mcg/min (6 ml/hr), increasing every 5 mins in steps of 10 mcg/min to a maximum of 75 mcg/min (45 ml/hr)
  • Note: if these infusions are not available quickly, IV GTN infusion 10-200 mcg/min (start high), is a good drug to start with
• Urinary catheter
• Urgent cardiology / cardiothoracic opinion if thoracic; or vascular surgery if adbominal dissection suspected

Key Management Decisions

• Intervention (surgical or endovascular) vs Medical
• Timing of Intervention – urgent vs chronic
  • Type A dissection is usually treated surgically; Type B medically (in absence of: malperfusion syndrome, ongoing pain, impending rupture or untreatable hypertension)
  • Endovascular management should be considered in complicated type B dissection

Background

Always consider the diagnosis if you hear aortic regurgitation, or a diastolic murmur

Introduction

• Acute aortic dissection is a medical and surgical emergency - it is one of the critical causes of acute chest pain that must not be missed!
• Aortic dissection now forms part of the ‘acute aortic syndrome’
• The inner wall of the aorta is composed of the tunica intima and the tunica media
• Damage to the intimal layer generates a space for blood to enter.  This ‘dissection’ of the intima-media layer allows the entry and flow of blood along the path of the aorta
• Presentation may be acute: <14 days; sub-acute: 14 days - 2 months; chronic: >2 months
• Type A prognosis is poor: 30% die immediately; 50% die <48h; 60% in-hospital mortality with medical management; 20-30% operative mortality; untreated, 1% die an hour, with 90% after 1 week
• In Type A dissection, 35% present with hypertension, 25% present with hypotension. In Type B, 70% present with hypertension, and 5% with hypotension
• 30% have acute aortic regurgitation
• A high index of suspicion is needed to diagnose in the emergency department; it is easily overlooked or misdiagnosed; it may mimic an MI
• Have a high index of suspicion in pregnant women presenting with chest pain

Definition

• Intimal damage resulting in generation of a false lumen within the aortic wall and propagation of blood along this space in either a forward or backwards direction

Pathology

• Myxoid degeneration - loss of elastic fibres and replacement of musculo-elastic tissue with proteoglycan-rich matrix
• Cystic medial necrosis: may be associated with injury or occlusion of vasa vasorum
• Intimal tear - dissection propagates along plane that runs between inner 2/3 and outer 1/3 of media 

Types

• Categorised anatomically, temporally (acute <14 days; subacute 14 days - 2 months; and chronic >2 months) or pathologically
• The aorta is divided into two parts, the thoracic and the abdominal aorta; the thoracic is further divided into the ascending part, the arch and the descending part
• The two commonly used anatomical classification systems are the Stanford and DeBakey systems (see figure below)
• Stanford: Type A and Type B:
  • Type A = ascending aorta affected
  • Type B = descending aorta affected
• DeBakey: Type I, II and III:
  • Type I and II = ascending + descending aorta
  • Type III = descending aorta
• Prognostically important, the Type A and Type I dissections carry the highest mortality and usually require acute surgical intervention 

Epidemiology

• 3-4 per 100,000 in UK/USA
• Male-to-female ratio is 2:1, to 5:1. Half in females before age 40y occur during pregnancy (typically in the 3rd trimester or early postpartum period)
• The peak age for Type A (proximal dissection) is 50-55 years, and that of Tyep B (distal dissection) is 60-70 years
• Classically at risk is a white, hypertensive man, age 50-70 years

Risk factors

Any process that weakens the wall of the aorta:

• Hypertension (70%) - leads to increased shearing forces across intima
• Traumatic injury to aorta (esp deceleration injury)
• Iatrogenic - surgery (eg AV replacement); cardiac catheterisation, aortic cannulation
• High cardiac output states: pregnancy
• Aortic disease: aortic aneurysm, anuloaortic ectasia, aortic arch hypoplasia, coarctation of the aorta, aortic arteritis (eg vasculitis (Giant cell, Takayasu's, Behcets), syphilis), bicuspid aortic valve
• Inherited defects
    - Marfan's - 15q fibrillin defect. Marfan syndrome accounts for the majority of cases of aortic dissection in patients < 40 years of age
    - Ehlers-Danlos - procollagen formation
    - Pseudoxanthoma elasticum - fragmentation of elastic fibres in media
    - Cardiac disease (bicuspid aortic valve)
    - Turner's and Noonan's syndrome
• Age/sex; 50-70 years; male sex 
• Competitive weightlifting
• Smoking, cocaine use

Pregnancy and Aortic Dissection

• Be highly suspicious of the diagnosis in a pregnant woman presenting with chest pain
• Any woman identified at risk (Marfans, coarctation, bicuspid AV and enlarged aorta, Ehlers Danlos Type IV etc) should have beta-blockade throughout pregnancy
• Patients with a known bicuspid aortic valve and enlarged aortic root should to be counselled like Marfan syndrome patients
• Normal sized patients with an aortic root size more than 4 cm (or smaller in patients with low BSA), or an increase of aortic root size during pregnancy, are at high risk for the occurrence of aortic dissection, mainly in the third trimester
• If possible, surgical repair of the enlarged aortic root should be done prepartum
• During pregnancy and during delivery, hypertension should be prevented
• Caesarean section under regional anaesthesia is recommended in all at risk patients. Then Aortic root surgery should be performed a few days after delivery, if it has not been performed prepartum
• In Type A dissection before 30 weeks of gestation immediate surgery should be performed, and after 30-weeks gestation caesarean section followed by cardiac surgery
• Close monitoring and the administration of beta-blocking agents is mandatory up to 3 months postpartum, as late dissections may occur in this time period

Effects of dissection

• Propagation
  • Aortic ring - acute aortic regurgitation (30%)
  • Coronary arteries - angina / MI
  • Carotid arteries - stroke
  • Abdominal aorta - gut ischaemia (if mesenteric vessels involved)
  • Renal artery - ARF
  • Intercostal / lumbar vessels - spinal cord ischaemia (loss of supply from arteria radicularis magna - great spinal artery of Adamkewicz)
• Rupture
  • Pericardium - tamponade
  • Pleura - haemothorax
• Compression
  • Trachea / oesophagus / SVC
• Double-barrelled lumen (if re-enters lumen through another intimal tear) 

Symptoms

• Can be varied and non specific; usually always chest pain (1/10 do not have pain – commonly patients with diabetes)
• Classic presentation is sudden onset of severe ‘stabbing’ or ‘tearing’ chest pain, radiating to the interscapular region. Interscapular pain usually suggests Type A dissection
• Chest pain that moves suggests dissection
• American Heart Association suggests ‘PEP’:
  • Pain character: sudden, tearing/stabbing pain in chest/back/abdomen
  • Examination findings: pulse/BP asymmetry, hypovolaemic shock, focal neurology, new aortic regurgitation.
  • Predisposing factors: Marfan’s, recent aortic surgery/procedure, thoracic aneurysm
• Of CCF (aortic regurgitation or MI)
• Other important features are a result of reduced perfusion:
  • LOC/collapse
  • Neurological focal deficit: dissection involving the carotids or low perfusion pressure
  • Ischaemic limb
  • Ischaemic end organ damage, eg ischaemic bowel, renal failure 

Key Questions

• “Describe the nature of the pain”
• “How quickly did it start”

Signs

• Shock, or hypertension (may have wide pulse pressure)
• New murmur (30% aortic regurgitation; early diastolic murmur)
• Of CCF (aortic regurgitation or MI)
• Cardiac tamponade
• Asymmetrical pulses (15-20%):
  • Pulse or BP deficit deficit between upper limbs
  • BP difference at upper and lower limbs
  • NB: absent pulses may reappear as the blood flow swtiches from the false to the true lumen
• Neurological signs - stroke, cord features
• Bruits over peripheral arteries
• Note: examination may be normal

Investigation

The key aim is to diagnose aortic dissection then assess its anatomy (Type A or B)

Blood

• FBC, U+E, LFT, Bone, Glucose, G&S
• CRP, ABG
• D-dimer (raised)
• Cardiac Troponin, if the patient presents > 6h after the onset of pain; may be raised if MI is diagnosis, or complication

Other

• ECG
  • Within 10 mins of presentation
  • Rule out acute or evolving MI - complicated dissection can induce MI (dissection may involve the origin of the coronary vessels)
  • May show LVH
  • May be normal (30%)
• CXR
  • 75% have classic changes including a wide mediastinum and prominent aortic knuckle; this is not a diagnostic sign, as many normal elderly patients have an unfolded aorta
  • Left pleural effusion (20%
  • Deviation of NG or tracheal to right
  • Separation of two parts of wall of a calcified aorta by > 5mm ('calcium sign')
  • May be normal (12%); or at least appear normal; with hindsight is almost always abnormal
  • Compare with previous films

 Note widened mediastium and left pleural effusion 

  'Calcium sign'

Key Investigations

• CT angiography is 100% sensitive, 98% specific and widely available 
• Transthoracic ECHO (if on-site cardiology available) to assess aortic root and valve in cases where type A is suspected (also to screen for pericardial effusion, aortic regurgitation; as this is quick and can be done at the bedside

CT with contrast demonstrating aneurysmal dilation and a dissection of the ascending aorta (Type A Stanford)

Specialist Investigations

• Transoesophageal echocardiography (TOE)
• MR angiogram may be better suited to monitoring established disease 

Differential Diagnoses

• Any sudden onset of chest and/or back pain
  • Cardiac (ACS, including acute MI, acute limb ischaemia)
  • Respiratory (massive PE, pneumothorax)
  • GI (peptic ulcer (+/-perforation), pancreatitis, mesenteric ischaemia, renal/ureteric colic)
• Neurovascular (e.g. stroke or cauda equina syndrome)
  Note: Neurovascular symptoms can also herald proximal aortic dissection

Treatment

Type A dissection is usually treated surgically; Type B medically

Treatment

• Resuscitate ABCDE
  • Adequate oxygenation and ventilation, two large bore cannulae, adequate intravenous fluid resuscitation titrated to blood pressure, heart rate and urine output
• IV MORPHINE 2.5-5 mg and IV METOCLOPRAMIDE 10mg
• High flow OXYGEN
• NBM
• If hypertension severe, control SBP to 100-120mmHg:
  • IV LABETOLOL (250mg/250mls 5% dextrose) at 2-8 mg/min, increasing every 15 mins to a maximum dose of 200mg; or
  • IV SODIUM NITROPRUSSIDE (50mg/500 ml 5% GLUCOSE) at 10 mcg/min (6 ml/hr), increasing every 5 mins in steps of 10 mcg/min to a maximum of 75 mcg/min (45 ml/hr)
  • Note: if these infusions are not available quickly, IV GTN infusion 10-200 mcg/min (start high), is a good drug to start with
• Urinary catheter
• Type A – emergency surgery: open repair = replacement of diseased segment of aorta with interpositional graft and re-implantation of coronary arteries if root involved +/- aortic valve replacement. Some centres use endovascular repair, or both
• Type B – classed as either complicated or uncomplicated
  • Uncomplicated: medical treatment; control SBP to 100-120mmHg (as above)
  • Complicated: co-incident rupture, ischaemia, uncontrolled pain or hypertension; for these patients intervention is with endovascular stent graft or open surgery

Indications for Surgery

• Emergency: Acute type A dissection
• Urgent: Subacute type A dissection
• Elective: Chronic type A dissection

Contraindications for Surgery

• Significant co-morbidity
• Chronic dementia
• Malignancy / terminal illness
• Irreversible profound brain injury 

Supportive Measures

• Pain results in catecholamine release; these mediators increase the pulse and BP
• Use opiates to alleviate pain

Key Management Decisions

• Intervention (surgical or endovascular) vs Medical
• Timing of Intervention – urgent vs chronic 
  • Type A dissection is usually treated surgically; Type B medically (in absence of: malperfusion syndrome, ongoing pain, impending rupture or untreatable hypertension)
  • Endovascular management should be considered in complicated type B dissection

Referrals

• Early involvement of cardiology, ITU and vascular and cardiothoracic surgeons
• Transfer to cardiothoracic surgical centre, if not in your hospital 

The Rest

No individual symptom or sign is diagnostic of aortic dissection

Maxim

• "Resuscitate and image quickly to determine optimal management and prevent complications" 

Complications

• Rupture of the aorta, with circulatory failure
• Stroke
• Visceral ischaemia, eg ischaemic bowel, limb or myocardial infarction
• Cardiac tamponade (secondary to rupture into pericardium) 

Follow up

• Aneurysm, re-dissection, rupture and graft complications are all long-term risks
• Regular magnetic resonance angiography should be performed to monitor for progression and the patient treated with lifelong anti-hypertensives 

Prognosis

• Type A have worse prognosis than Type B
• Type A prognosis is poor: 30% die immediately; 50% die <48h; 60% in-hospital mortality with medical management; 20-30% operative mortality; untreated 1% die an hour, with 90% after 1 week
• Of patients who make it out of hospital alive 30-60% survive ten years

Secondary Prevention

• Lifelong antihypertensive therapy

Don’t forget

• No individual symptom or sign is diagnostic
• Examination, ECG, CXR may be normal
• Compare CXR with previous ones
• 75% have widened mediastinum; ie 25% do not
• Request imaging ASAP
• As may mimic an MI, diagnosis requires a high index of suspicion. Thrombolysis not helpful

Red Flags

• Type A dissection
• Severe hypo- or hypertension

References