Aortic Dissection

Always consider aortic dissection as 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: 2 months
  • Type A aortic dissection 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

What is aortic dissection

aortic dissections

 

  • 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

Aortic Dissection Types

  • Categorised anatomically, temporally (acute 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:
  1.       Type A aortic dissection = ascending aorta affected
  2.       Type B aortic dissection = 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 of Dissecting Aortic Aneurysm

  • 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
  1.   – Marfan’s – 15q fibrillin defect. Marfan syndrome accounts for the majority of cases of aortic dissection in patients < 40 years of age
  2.   – Ehlers-Danlos – procollagen formation
  3.   – Pseudoxanthoma elasticum – fragmentation of elastic fibres in media
  4.   – Cardiac disease (bicuspid aortic valve)
  5.   – 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 Aoric 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)

Aoric Dissection 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”

Aortic Dissection 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 for Aortic Dissection

  • 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%)

aortic dissection chest x ray

 

aortic dissection radiography

 

  • 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 Diagnosis

  • 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 of Aortic Dissection

Type A dissection is usually treated surgically; Type B medically

  • 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

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:

  1. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM Guidelines for the Diagnosis and Management of Patients With Thoracic Aortic Disease. J Am Coll Cardiol, 2010; 55: 27-129
  2. ESC/Diagnosis and management of aortic dissection. Recommendations of the Task Force on Aortic Dissection, European Society of Cardiology. Erbel R et al. European Heart Journal 2001; 22: 1642–1681

Be the first to comment

Leave a Reply

Your email address will not be published.


*