FRCA Notes

Aortic dissection

Resources

  • Aortic dissection is disruption of the tunica intima of the aorta, provoked by intramural bleeding
    • This results in separation of the layers of the aortic wall, leading to formation of a false lumen ± communication with the true lumen
    • Tracking of blood in a dissection plane within the tunica media can occur, either anterograde or retrogradely
    • It can then either rupture (if adventitia disrupted) or re-enter the aortic lumen through a second tear in the tunica intima

  • The incidence ∽6 per 100,000/yr
    • Higher in men (yet poorer prognosis in women due to atypical presentations and delayed diagnosis)
    • Increases with age

Stanford - Type A and Type B

  • Type A dissections involve the ascending aorta and are surgical emergencies
  • Type B dissections involve any part of the aorta distal to the origin of the left subclavian artery

De Bakey - based on the location of the intimal tear

  • Type I: intimal tear in the ascending aorta; involves all portions of the thoracic aorta
  • Type II: intimal tear in the ascending aorta; involves the ascending aorta only, stopping before the innominate artery
  • Type III: intimal tear in the descending aorta, starting distal to the left subclavian artery but can propagate proximally into the arch

Comorbidities

  • Hypertension (65 - 75% of patients), especially if it's poorly controlled
  • Hypercholesterolaemia
  • Advanced age
  • Smoking
  • Cocaine
  • Amphetamine
  • Pregnancy
  • Pre-existing aortic disease e.g. coarctation, aneurysm, aortic valve pathology
  • Vasculitides e.g. giant cell arteritis, Takayasu arteritis, syphilis
  • Connective tissue diseases e.g. Marfan's syndrome, Ehlers-Danlos syndrome, Turner's syndrome

Trauma

  • Iatrogenic e.g. aortic surgery or cannulation
  • Blunt chest trauma inc. fall from height
  • Deceleration injury e.g. RTC

Presenting features

  • Chest pain occurs in 70 - 80% of patients
    • Its most specific characteristic is an abrupt onset
    • Severe chest ± back (40%) ± abdominal (25%) pain
      • Chest pain is associated with Type A dissection
      • Back and abdominal pain are more frequent in Type B dissection
    • Sharp, ripping, knife-like or tearing
    • Radiating pain (15 - 20%)

  • Hypotension (15 - 30%)
  • Tachycardia
  • Diastolic murmur
  • There may be outright shock on account of aortic rupture, acute severe MR, extensive MI, cardiac tamponade or major haemorrhage

Associated cardiovascular features

Vascular area involved Clinical sequelae
Aortic valve Aortic regurgitation (40 - 75%)
Coronary ostia Coronary ischaemia (10 - 15%)
Carotid or brachiocephalic arteries Syncope (5 - 15%) , stroke (10%) or seizure
Subclavian artery Upper limb ischaemia
Intercostal → spinal arteries Spinal cord (≤1%) or lower limb ischaemia (≤10%)
Coeliac trunk and mesenteric arteries Abdominal pain,  bowel ischaemia (5%)
Renal arteries Flank pain,  AKI (10 - 20%)
  • Pericardial tamponade occurs in 20% of Type A dissections and is associated with a doubling of mortality
  • Congestive cardiac failure (10%) may occur secondary to new AR in the context of existing ventricular dysfunction

Neurological features

  • Overall frequency 15 - 40%, though are only transient in half of cases
  • They arise from a combination of cerebral hypoperfusion, distal thromboembolism or nerve compression

  • Syncope (5 - 15%)
  • Stroke (10%)
  • Acute paraplegia from spinal ischaemia (1%)
  • Acute limb ischaemic neuropathy (10%)
  • Hoarse voice from compression of left recurrent laryngeal nerve (rare)

Intra-abdominal features

  • Mesenteric ischaemia (5%)
    • Non-specific abdominal pain
    • 40% are painless and may lead to late diagnosis with high mortality
    • If present is associated with a 3x increase in mortality
  • Acute kidney injury (10 - 20%), due to:
    • Renal hypoperfusion
    • Dissection of the renal arteries
  • Massive upper GI bleeding can occur due to aorto-oesophageal or aorto-enteral fistulae

Respiratory features

  • Overall rare
  • Small pleural effusions due to activation of the inflammatory process (15 - 20%); large effusions are rare as these patients die pre-hospitally
  • Massive haemoptysis from acute aortic rupture into the lung
  • Compression of the pulmonary artery can cause dyspnoea and unilateral pulmonary oedema

  • A full medical history and physical examination, naturally

  • Bloods:
    • FBC for Hb
    • CRP
    • U&E - is there an AKI?
    • LFTs - is there an ischaemic liver injury?
    • Troponin to assess for myocardial ischaemia
    • CK - is there reperfusion injury ± rhabdomyolysis
    • D - dimer; typically very high immediately (vs. slow rise in other conditions) and yields the highest diagnostic value within the first hour
    • Group & save

  • A blood pressure in both upper limbs
  • If a radial arterial line is required, use the right radial

Imaging

  • ECG - there will be ischaemic changes in 20%
  • CXR - widened mediastinum, small pleural effusions
  • TTE or TOE
  • CT aortogram

  • The physiological goal of management is to limit stress on the aortic lumen, by reducing both LV contractility and systolic blood pressure

  • Analgesia e.g. titrated morphine, which will reduce pain exacerbating hypertension

  • Reduce blood pressure to a target systolic 110 - 120mmHg, using:
    • β-blockers in the first instance e.g. labetalol, metoprolol, esmolol
    • Peripheral vasodilators e.g. GTN, sodium nitroprusside, hydralazine
    • Calcium channel blockers if β-blockers contra-indicated

Type A Dissection

  • Surgery is the treatment of choice as there is a 50% mortality at 48hrs if not operated on
    • Improves 1-month mortality from 90% to 30%
    • Still associated with perioperative neurological complications (18%) and mortality (25%)

Type B Dissection

  • Often uncomplicated and medical therapy alone may suffice, with close observation to identify disease progression or malperfusion syndromes
  • Repair of complicated Type B dissection includes T-EVAR, which improved long-term mortality vs. medical therapy alone
  • Open surgery is reserved for those with acute complicated Type B dissection not amenable to IR approach
    • Complication rates from open surgery are greater than T-EVAR
    • Type B dissection surgery involves left lateral thoracotomy and DLT

Monitoring

  • AAGBI
  • Large bore peripheral access
  • Radial arterial line (right)
  • CVC
  • Continuous TOE monitoring

Cerebral protection

  • DHCA (18 - 20°C) with head packed in ice
  • Limit cross-clamp duration
  • Continued cerebral perfusion (anterograde/retrograde)
  • Possibly: methylprednisolone, thiopentone, lidocaine
  • Protective effects of volatile agents (ischaemic preconditioning)
  • Mannitol (oxygen radical scavenging)
  • pEEG monitoring

Coagulopathy

  • Coagulopathy can occur from major haemorrhage, massive transfusion, the effects of DHCA or CPB

Post-operative

  • Admission to cardiac ICU
  • Standard post-bypass care
  • Post-operative ECG and CXR
  • Observation for, and management of, complications such as metabolic acidosis, visceral ischaemia, infection and pulmonary complications

  • Patients with acute Type A dissection suffer double the mortality of individuals presenting with Type B dissection (25% and 12%, respectively)
  • Commonest causes of death are aortic rupture or severe regurgitation

  • Surgically repaired Type A dissection has a 96% survival at 1yr, and 91% survival at 3yrs

Poor prognostic factors at presentation

  • Age >70yrs
  • Hypotension | shock | tamponade
  • Pre-operative massive transfusion
  • Pre-operative AKI
  • Previous MI
  • Abnormal ECG