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Entries in Surgery (1)

Thursday
Dec152011

EMRAP Spotlight C3 - Aortic Dissection

Michael Ellis DeBakey (1908-2008)

Michael Ellis DeBakey (September 7, 1908 – July 11, 2008) was a world-renowned Lebanese-American cardiac surgeon, innovator, scientist, medical educator, and international medical statesman.

He also lends his name to the DeBakey classification of aortic dissection....

This is a potentially lethal condition of the aorta. Untreated, estimated mortality is approximately 1 % per hour for the 1st 48 hours, and 90% at 3 months.

This months EMRAP C3 Project focuses on aortic dissection, with an excellent round up and summary by Rob Rogers MD, and Amal Mattu (with some emphasis by Mel Herbert, and myself). Head over to EMRAP and check out the discussion. 

Below is a summary of my own notes on aortic dissection.

Classification

DeBakey Classification

  • Type I - Originates in ascending aorta, propagates at least to the aortic arch and often beyond it distally.
  • Type II - Originates in and is confined to the ascending aorta
  • Type III - Originates in the descending aorta and extends distally down the aorta or, rarely, retrograde into the aortic arch and ascending aorta

 Stanford Classification

  • Type A - All dissections involving the ascending aorta, regardless of site of origin
  • Type B - All dissections not involving the ascending aorta.  

Predisposing factors

  • Hypertension
  • Aortic stenosis
  • Connective tissue disorders
  • Congenital cardiovascular disorders 

Clinical Features

  • Pain occurs in the majority of patients
  • Severe, tearing, ripping in nature
  • Pain may migrate which may indicate proximal or distal extension (into lower back, or neck jaw)
  • Coma
  • Confusion
  • Neurological deficits that mimic stroke (? carotid involvement)
  • Syncope
  • Essentially a clinical diagnosis

Investigation

Bedside

  • ECG - AMI is the main differential

Pathology

  • D-dimer has been reported to have a high sensitivity in selected groups, although no test has yet been validated for diagnostic purposes

Imaging

Chest X-ray findings :

  • Widening of mediastinum
  • Dilation of aortic arch 
  • Obliteration of the aortic knob 
  • Double density of aorta (? false lumen)
  • Displacement of trachea to the right
  • Distortion of left main-stem bronchus
  • Pleural effusion (more common left sided)
  • Cardiomegaly

 CT Angiography

  • Reconstruction of aorta
  • Preferred study in stable patients
  • Look for intimal flap 
  • High sensitivity and specificity (maybe as high as 93-98%)
  • Can identify complications

 ECHO

  • TTE has low sensitivity and specificity 
  • TOE now preferred
  • Available at bedside, though patient requires sedation and advanced airway control
  • Contraindicated in patients with oesophageal varices, or tumours

 MRI

  • highly sensitive and specific
  • Lesser availability than CT
  • Unsuitable for unstable patients

Management

Medical 

Main aim to decrease the pulsatile stress on the aortic wall, which is determined by systolic BP and velocity of flow.

Aims - Systolic BP 100-120mmHg, HR 60-80 BPM

  • analgesia - titrated opiate
  • Beta-blockade - esmolol is ideal choice.
  • 500mcg / kg bolus + 50mcg / kg / min
  • If increase is required, give further 500mcg / kg bolus, and increase infusion rate by 50mcg / kg / min e.g 500mcg / kg bolus + 100mcg/ kg / min
  • Vasodilator such as sodium nitroprusside, IV infusion 0.5 - 10 mcg / kg / min (not beyond 24 hours. Should be commenced AFTER beta-blockade due to reflex tachycardia
  • Titrate to pain relief, or signs of shock.

 Surgical

  • Type A - immediate surgery
  • Type B - traditionally medical management

Indications for surgical management in type B

  • Leaking aorta
  • Organ ischaemia
  • Marfan’s syndrome
  • Extension of dissection
  • Intractable pain & hypertension
  • Aortic dilatation > 5cm

 Disposition

  • ICU / HDU
  • Theatre
  • Transfer to specialist unit

The International Registry of Acute Aortic Dissection (IRAD), Hagan PG et al, JAMA, February 16  2000-vol 283, 897-903 

Acute Aortic Dissection, Golledge J, Eagle KA, Lancet 2008; 372: 55–66