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:

10-40% normal
widened upper mediastinum
left pleural effusion
increase in cardiothoracic ratio due to pericardial effusion

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