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aorticdissection_dx

aortic dissection features and diagnosis

historical perspective:

  • in 1761, Nicholls described aortic dissection in an autopsy on the body of Kng George II of England, who is reported to have died straining at stool.
  • in 1761, Morgagni gave the 1st clear, pathologic description
  • in 1819, Laennec 1st used the term anaeurysm disseguant resulting in the inaccurate term dissecting “aneurysm”
  • in 1856, Swaine & Latham made the 1st antemortem diagnosis
  • in 1935, Gurin et al made the 1st attempt at surgical therapy
  • in 1955, the modern era of Dx & Rx begins with DeBakey et al outlining the pronciples that remain the basis for surgical Rx
  • in 1965, Hirst et al introduced a Rx regime of medical Rx that, in one form or another, is still the Rx of choice for certain types of dissection
  • in 2003, Weber et al investigated the use of D-Dimer to rule out Dx of dissection.
  • in 2010, aortic dissection decision tool (ADD) developed based upon retrospective data of positive cases, no specificity determined

prognosis

  • 40% die immediately (whereas 75% of patients with ruptured AAA reach an ED alive)
  • 1% die per hour thereafter
  • untreated mortality is > 90%
  • 5-20% die during or shortly after surgery
  • only 50-70% will be alove 5 years after surgery
  • 2-3 x as many people die from aortic dissection as they do from ruptured AAA 1)
  • poor prognostic factors 2):
    • age > 65 yrs
    • Type A dissection
    • BP < 90mmHg
    • neutrophilia > 80%
    • elevated D-Dimer > 5mg/L

epidemiology:

  • incidence 5-10 per million pop. per year
  • ~40-50 people die in Australia each year from aortic dissection
  • 2-3 x incidence of ruptured AAA
  • men 2-3 x women
  • may be higher in African-Americans
  • ~70% have PH hypertension which is often uncontrolled
  • 15% have a bicuspid aortic valve
  • familial incidence
    • 13-19% of all people with aortic dissection without an identified genetic syndrome have 1st degree
  • most cases occur 50-70yrs age (but as young as 14 reported!!)
  • relatively rare before 40yrs (only 7% are under 40yrs) unless predisposing condition:
    • Marfan syndrome (1/3rd develop dissection):
      • CT disorder assoc. with long, thin habitus, lenticular dislocations, high-arched palate, arachnodactyly, chest wall deformities
      • accounts for 50% of those with aortic dissection under age 40 years
      • most patients with Marfan syndrome present with dilatation of the aortic root/ascending aorta or Type A dissection
    • Ehlers-Danlos syndrome:
      • CT disorder assoc. with fragility, hyperelasticity & easy bruisability
      • the vascular form of Ehlers-Danlos syndrome is a rare autosomal dominant disorder characterized by easy bruising, thin skin with visible veins, characteristic facial features, and rupture of arteries, uterus, or intestines.
      • rupture of the gastrointestinal tract is more likely to occur prior to arterial rupture
    • Loeys-Dietz syndrome
      • an autosomal dominant aortic aneurysm syndrome with involvement of many other systems
      • mutations in either the transforming growth factor receptor Type I or II (TGFBR1 or TGFBR2) genes
      • characterized by the triad of arterial tortuousity and aneurysms, hypertelorism and bifid uvula or cleft palate, or a uvula with a wide base or prominent ridge on it.
      • mean age of death of 26 years
    • Turner syndrome:
      • 10-25% of patients with Turner syndrome have a bicuspid aortic valve
      • average age of aortic dissection in Turner syndrome was 31 years, with >50% mortality
    • cong. heart disease:
      • esp. Ebstein's anomaly, aortic valve stenosis, bicuspid aortic valve, patent foramen ovale, coarctation aorta
      • 1-2% of population have biscuspid aortic valve
        • incidence of dissection in pts with bicuspid aortic valve is 9x that in pts with tricuspid aortic valve
      • 25% of patients with untreated coarctation aorta will develop dissection
      • patients with aberrant R subclavian artery develop dysphagia and are at increased risk of dissection
      • 0.5% of the population have a right sided aortic arch and these are at risk of dissection
    • familial incidence
    • pregnancy (accounts for 50% of dissections in women under 40yrs)
    • coarctation of aorta - probably due to upper extremity hypertension
    • Turner syndrome
    • cocaine or other stimulant use
    • weight lifting or other Valsava manouvre
    • trauma:
      • cardiac surgery or catheterisation
      • blunt trauma from sudden deceleration - but usually cause aortic rupture rather than dissection
  • risk factors in addition to above:
    • systemic hypertension (present in >2/3rds of pts, esp. if distal dissection)
    • polycystic kidneys
    • chronic steroid use or immunosuppression
    • vasculitis - esp. Takayasu arteritis, giant cell arteritis, and Behcet arteritis

pathophysiology:

  • an aortic dissection is a longitudinal cleavage of the aortic media by a dissecting column of blood as a result of:
    • medial degeneration:
      • occurs with age esp. in pts with hypertension & in those with dissections
    • repeated flexion of heart with each heart beat:
      • with each heart beat, the heart swings side to side due to limitation in the AP direction, causing a flexing in both the ascending aorta & in descending aorta just distal to the left subclavian artery where it becomes tethered.
    • pulsatile hydrodynamic forces:
      • affects ascending aorta primarily
    • exacerbated by:
      • hypertension incl. upper extremity hypertension due to coarctation aorta
      • hyperdynamic states eg. pregnancy
      • CT diseases such as Marfan's
      • disruption of laminar flow eg. bicuspid valve
  • three variants:
    • intimal tear which allows blood access to the media occurs in > 70% of cases
    • intramural haematoma presumed due to blood from initially from ruptured vaso vasorum haemorrhaging into media (up to 15% of cases)
    • penetrating atherosclerotic ulcer (up to 15% of cases)
  • once a dissecting haematoma is established in the aortic media, migration occurs in either anterograde or retrograde direction forming a “false lumen” in the outer half of the media which may then either:
    • rupture back into the true lumen resulting in a rare “spontaneous cure”
    • rupture out of adventia into pericardial sac or pleural cavity
  • factors favoring continued dissection are:
    • degree of elevation of BP
    • steepness (slope) of pulse wave (dP/dT)

classification:

  • acute if < 2wks duration, chronic if > 2wks duration
    • ~75% of pts with untreated dissection die within 2wks of onset of symptoms
  • anatomic classification is important both from a diagnostic & therapeutic viewpoint

DeBakey classification:

  • type I:
    • involve ascending aorta, arch, & descending aorta
  • type II:
    • confined to ascending aorta
  • type III:
    • confined to descending aorta distal to left subclavian artery
    • IIIA: stay above diaphragm
    • IIIB: propagate below diaphragm

Stanford classification:

  • Type A:
    • involve ascending aorta
    • these are much more lethal & have a different approach
    • accounts for 2/3rds of dissections
  • Type B:
    • do not involve ascending aorta
    • 1/3rd of dissections
    • generally older pts, smokers with chronic lung disease, often have generalised atherosclerosis, more often hypertensive

history:

  • 90% have pain (if not present pt is either unconscious, elderly or has neurologic deficit that impairs pain perception such as a stroke):
    • usually excruciating, sharp, stabbing, tearing, or ripping, with abrupt, severe onset
    • asc. aorta ⇒ ant. chest pain (71% of Type A dissections present with anterior pain)
    • arch aorta ⇒ pain in neck & jaw
    • desc. aorta ⇒ interscapular pain (32% of Type A dissections present with posterior chest pain)
    • infradiaphragmatic aorta ⇒ lumbar/abdominal pain (47% of Type A and 64% of Type B present with back pain, while 21% of Type A and 43% of Type B present with abdominal pain)
    • pain often migrates according to anatomic location of dissection as above, although less than 50% report it as being migratory
  • commonly have vasovagal symptoms - sweating, N/V, light-headedness, severe apprehension
    • 5% have syncope early:
      • esp. if ascending aorta involved & usually heralds dissection into pericardium causing cardiac tamponade
      • may be due to:
        • cardiac causes: severe aortic regurgitation, ventricular outflow obstruction, cardiac tamponade
        • vascular causes: impaired cerebral blood flow and aortic baroreceptor activation
        • neurologic causes: vasovagal in response to pain
        • volume-related / hypovolaemia: false lumen rupture into the pleural space
  • 20% present with neurologic deficit:
    • stroke
    • spinal cord ischaemia
    • peripheral nerve ischaemia
  • >75% have PH chronic hypertension
  • late presentations involving distal aorta:
    • may present as epigastric pain with vomiting +/- fever, hypotension and raised inflammatory markers followed by back pain as it further progresses

examination:

  • generally pt is very apprehensive with tachycardia & signs of inadequate end-organ perfusion even in the face of an elevated BP
  • hypertension may be exacerbated by catecholamine release & may be severe if dissection involves renal arteries causing renin release
  • if hypotensive then consider:
    • hypovolaemia
      • look for pericardial friction rub, jugular venous distension, pulsus paradoxus, muffled heart sounds, tachycardia
    • impaired circulation to limbs (esp. arms) causing pseudohypotension:
      • look for pulse deficits (occur in 50% dissections) & carefully document pulses & re-examine frequently
      • may be due to either:
        • intimal flap covering true lumen of branched vessel
        • dissecting haematoma compressing an adjacent true lumen
    • vasovagal
    • conduction defect
  • aortic regurgitation occurs in 50% with type A dissections:
    • murmur may have musical, vibrating quality with variable intensity
    • congestive heart failure may develop
  • neurologic findings are common:
    • altered sensorium
    • hemiplegia, hemianaesthesia, gaze preference to affected side
    • ischaemic paraperesis occurs in 4% due to interuption of blood flow to intercostal, lumbar & ant. spinal arteries
    • ischaemic peripheral neuropathy if obstruction of vessel supplying limb
  • uncommonly:
    • haemoptysis (rare)
    • hoarseness due to compression on recurrent laryngeal nerve
    • Horner's syndrome
    • superior vena cava syndrome
    • aorto-oesophageal fistula ⇒ haematemesis
    • bronchospasm due to bronchial/tracheal compression
    • mesenteric infarction & AMI

likelihood ratios

risk stratification:

investigations:

routine lab. tests:

D Dimer

  • early, small studies suggested a sensitivity > 95% but recent studies suggest sensitivity appears to be only ~ 82%3) when using a cutoff of 400mcg/L and relatively low specificity (as may be raised with infection, PE, AMI, etc)
    • in the false negative group, D-Dimer was sampled within 72 minutes of onset of symptoms - perhaps there needs to be more delay in sampling as with troponin sampling in acute coronary syndromes.
  • Shimony et.al. has shown that a d-dimer level <500 ng/ml has good exclusion ability (negative likelihood ratio 0.06, 95% CI 0.03 to 0.12, I2<0.001), whereas positive likelihood ratio showed a poor discriminative ability (2.43, 95% CI 1.89 to 3.12, I2 < 0.78). 500 ng/ml is also the currently accepted cut-off level of VTE and the standard for most commercially available kits and laboratory assays. However a small intimal tear and minimal false lumen may not have enough clot load to raise the d-dimer above 500 ng/ml. 4)
  • a negative D-Dimer appears to be sufficient to rule out dissection if the ADD score is 0 or 1.5)

ECG:

  • commonly shows LVH reflecting long-standing HT
  • useful in excluding AMI, however, 10-40% pts with dissection may have ECG abn. suggesting ischaemia or infarction
    • 8% pts with type A diseections have ST elevation (nil with type B).
    • more commonly ST depression occurs
  • heart block may be present from retrograde dissection into interatrial septum with compression of AV node

CXR:

  • routine CXR's abnormal in 80-90% pts:
  • mediastinal widening 75% - distinguish from tortuosity of chronic HT
    • other causes of widened mediastinum:
      • Xray beam too close
      • neoplasia
      • mediastinal haemorrhage:
        • leaking saccular aortic aneurysm
        • mediastinitis
  • “calcium sign” uncommon but highly specific - calcium > 5mm from outermost portion of aorta
  • double-density appearance suggesting 2 channels
  • localised bulge of aorta
  • obliteration of aortic knob
  • displacement of trachea or NGT to right
  • pleural effusion - common, esp. on left - inflammatory or haemothorax
  • check with previous CXRs

echo:

transthoracic:

  • sensitivity 77-80%, specificity 93-96% ⇒ too many false negatives

transoesophageal:

  • sensitivity 97-100%, specificity 90-100%
  • can be some difficulty evaluating asc. aorta & prox. arch due to interposition of air-filled trachea & left main bronchus ⇒ use of newer biplane probes
  • quick, easily performed at bedside
  • few serious side effects
  • excellent at detecting pericardial fluid

CT:

  • 5% false positives & 5% false negatives although newer generation CT scan studies suggest sens. near 100% and spec. 98-99%
  • scan should be done without contrast initially to detect subtle changes of an intramural haematoma
  • contrast scan is then done looking for:
    • dilatation of aorta
    • presence and extent of an intimal flap
    • differential rates of flow in true vs false channels
    • clear demonstration of both false & true lumina
    • regions of potential malperfusion
    • contrast leak indicating rupture
  • disadvantages:
    • no info. on presence of aortic regurg. which is important in determining appropriate Rx
    • no info. on relationship of dissection to major branches of aorta
    • must move pt to radiology dept

normal ranges of mean adult aorta diameter on CT

  • root: 3.50-3.72cm (female); 3.63-3.91cm (male)
  • mid-descending: 2.45-2.64cm (female); 2.39-2.98cm (male)
  • diaphragmatic: 2.40-2.44cm (female); 2.43-2.69cm (male) 6)

aortography:

  • gold standard but invasive and requires a catheter be inserted into a potentially abnormal aorta
  • accurately determines site of intimal tear & aortic regurgitation
  • the only Ix that demonstrates the extent & location of dissection on aortic side branches

MRI:

  • excellent sensitivity/specificity
  • shows site of intimal tear, type & extent of dissection, presence of aortic regurg., differential flow rates in true & false channels, & in aortic side branches.
  • image acquisition prolonged, no metal objects nearby thus cannot provide ECG monitoring, intra-arterial pressure monitoring
  • if gadolinium agents used, small risk of nephrogenic systemic fibrosis

coronial reports of misdiagnosis

3)
Paparella et al. J. Cardiovasc. Med. Volume 10(2), February 2009, p 212–214
4)
Shimony, A., et al., Meta-Analysis of Usefulness of D-Dimer to Diagnose Acute Aortic Dissection. The American journal of cardiology, 2011. 107(8): p. 1227-1234.
6)
Johnston et al.
aorticdissection_dx.txt · Last modified: 2019/10/30 15:35 (external edit)