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Aortic dissection

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Anna Lee & Charles Gomersall

Updated February 2006

Definition

Condition produced by penetration of circulating blood into the wall of aorta for a varying degree (³ 1 cm)

Epidemiology

  • Incidence: 1-6/100 000/yr
  • Age: majority between 40 and 70 yrs
  • Sex: 2-5 times more common in men
    Race: commoner in negroes (probably due to increased incidence of hypertension), rare in orientals
  • Associated conditions: hypertension, pregnancy, coarctation of the aorta, bicuspid aortic valve, Marfan’s
  •  Mortality: 1-2% per hour after symptoms onset for the first 24 hours for Type A dissection, and 30-day mortality of 10% for type B dissection

Pathogenesis

  • Vessel abnormality. Cystic medianecrosis in up to 92% of cases: cause obscure. Syphilis and hypertension not thought to be involved in vessel abnormality
  • Pressure abnormality. 63% of patients hypertensive
  • Trauma. May result in acute dissection but role in dissection at a later date is disputed

Classification

De Bakey: type I - ascending and descending aorta; type II - ascending only; type III - distal to left subclavian artery

Stanford University: type A - ascending ± descending; type B - descending beyond origin of left subclavian only. Classification based on part of aorta that is involved in dissection not on site of intimal flap.

Acute/chronic: acute - diagnosis made within 2 weeks of onset of symptoms; chronic - >2 weeks

Clinical features

  • chest pain
    • most common presenting complaint
    • midline. May be felt at front or back depending on site of dissection
    • usually sudden onset and reaches maximal intensity immediately. This abruptness is the most specific characteristic of the pain
    • ripping, tearing, choking, stabbing
    • radiates to back or along involved vessels. Does not commonly radiate to neck, shoulder or arm
    • absent in ~5-10% of cases
    • return of pain after a pain-free period usually indicates impending rupture
  • hypertension
    • most patients hypertensive due to pre-existing hypertensive disease or increased sympathetic drive
    • ~25% hypotensive due to:
      • acute aortic regurgitation
      • cardiac tamponade
      • left ventricular systolic failure

Features due to organ system involvement

Due to ischaemia because of obstruction of branches of aorta, direct compression of organ by expanding false lumen or leak or rupture of false lumen into surrounding structures (usually rapidly fatal). Most commonly results in cardiovascular and neurological involvement.

Cardiovascular

  • pulse and blood pressure differential between two arms. Most specific sign but only occurs in ~20% of patients. An ominous sign associated with increased mortality
  • aortic regurgitation. If severe presents with cardiogenic shock
  • acute pericardial effusion or cardiac tamponade
    • in most cases not due to rupture into pericardial cavity but to transudation of fluid into pericardial cavity through intact wall of false lumen
    • ominous sign
  • left ventricular systolic failure
  • hypotension
  • carotid, subclavian and femoral bruits

Neurological

  • cerebral ischaemia/stroke most common feature
  • syncope
  • spinal cord lesion
    • more common with distal dissections

Investigations

CXR

May show:

Aortography

  • sensitivity of 86-88%
  • specificity 75-94%
  • can locate intimal tear
  • delineates longitudinal extent of false lumen
  • allows for assessment of blood flow in important branches of aorta
  • can quantify any aortic regurgitation
  • as a diagnostic tool, superceded in recent years by other imaging techniques but is the standard technique for guiding percutaneous intervention

CT (contrast)

Images

  • sensitivity 90%, specificity 85%
  • allows quick assessment of true and false lumina and intimal flap
  • can reliably diagnose pericardial and pleural effusions and distinguish between serous and haemorrhagic effusions
  • sensitivity lower for ascending aortic tears
  • helical CT superior to conventional CT. Also allows 2-D and 3-D reconstructions - useful in visualizing course of dissection membrane in aortic arch relative to origin of subclavian artery
  • provides no information on aortic regurgitation

Echo

  • transthoracic
    • only really of value in diagnosing complications such as tamponade and aortic regurgitation
  • sensitivity 80%, specificity 90%

  • TOE
    • can establish diagnosis at bedside, visualize intimal flap and provide information regarding extent and type of dissection, entry tear, aortic valve, coronary ostia and LV function
    • highly user dependent
    • quoted sensitivity 98%, specificity 99%

MRI

  •  highest sensitivity and specificity for detection of all forms of dissection (95-100%)
  • can provide useful information about flow in true and false lumens
  • not suitable for severely ill patients and main role is in chronic dissection and post-surgical follow up

ECG

  • ± LV strain due to hypertension
  • non-specific ST and T wave changes

Serum smooth muscle myosin heavy chain

  • early data suggest that this may prove to be a useful screening test in patients presenting within a few hours of dissection

Differential diagnosis

  • MI
  • PE
  • mesenteric arterial or venous thrombosis
  • peptic ulcer
  • acute appendicitis
  • gastric CA
  • intestinal obstruction
  • pancreatic/peritoneal cyst
  • acute cholecystitis

Treatment

The aim of therapy is to prevent rupture and to relieve branch vessel ischemia

Immediate management

  • control of BP
    • recommended target SBP 100-120mmHg
    • reduce to lowest levels compatible with adequate peripheral perfusion with IV beta-blockers or combined alpha-beta blocker (eg esmolol, labetalol) ± nitroprusside. Do not use latter alone as this may result in an increase in velocity of ventricular contraction and extension of the dissection. Once BP is controlled perform CT or TOE
  • pain relief with morphine

Definitive treatment

  • all dissections involving ascending aorta should be treated by early surgery unless there is a contraindication to surgery. NB stroke is not a contraindication to surgery as many patients recover without neurological deficit. Surgery associated with a 15-35% mortality rate; may approach 70% in patients with complications. 10 year survival 40-60%
  • descending aortic dissections usually treated medically (survival rate about 75% whether treated surgically or medically). Surgery for those with complications such as leakage of blood from aorta, decreased blood supply to an organ or limb, intractable pain despite adequate medical treatment, and rapidly expanding aortic diameter on CXR. Paraplegia is not an indication as recovery is unusual following repair. Medical treatment consists of BP control

Percutaneous intervention

Includes stent-graft placement and percutaneous balloon fenestration

  • Stent graft

    • Used to seal off the entry tear, thus inducing thrombosis of the false lumen and stabilizing the dissection

    • Reverses organ ischemia in 50%

    • Often need to combine with balloon fenestration for renal and mesenteric ischemia, which are not usually well reversed well by stenting alone

  • Percutaneous balloon fenestration

    • Creates a reentry tear in the dissection flap, improving blood flow to compromised branches which derive their supply exclusively from the false lumen

    • Complications - paraplegia, endovascular leakage and aortic wall perforation

    • Indication - as an alternative to surgery in unstable descending aortic dissection; for relief of organ malperfusion – hepatic, renal, lower extremities or spinal ischemia – either before or after surgical treatment for both ascending and descending aortic dissection

    • Results – Flow restored in >90% of vessels obstructed. 30-day mortality 10% (0-25%). Safer and produce better result than surgical graft stent

Prognosis

  • hospital mortality ~30% for patients with dissections proximal to origin of left subclavian and ~10% for distal dissections
  • risk factors for death:
    • age>65 yrs
    • proximal dissection
    • migrating characteristic of pain
    • shock
    • pulse deficits
    • presence of organ ischemia
    • neurological deficits
    • iatrogenic dissection during cardiac surgery or catheterization

Intramural haematoma of thoracic aorta

  • localized haematoma within aortic wall without extensive proximal or distal extension or the presence of an intimal tear
  • clinical presentation similar to aortic dissection
  • CXR usually shows a widened mediastinum
  • CT/MRI/TOE/angio: no evidence of dissection or intimal tear
  • consider early surgery for ascending aortic haematoma and patients with persistent pain
  • medical treatment for patients with descending aortic haematoma

Further reading

Khan IA, Nair CK. Clinical, diagnostic, and management perspectives of aortic dissection. Chest, 2002; 122:311-28

Endoluminal treatment of aortic dissection. Eur Radiol 2003; 13:2521–2534

Diagnosis and management of aortic dissection - Recommendations of the Task Force on Aortic Dissection, European Society of Cardiology. European Heart Journal (2001) 22, 1642–1681


© Charles Gomersall November 1999, September 2003; © Anna Lee, Charles Gomersall February 2006


©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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