see also:

• ADD - an aortic dissection risk assessment tool
• Mx of aortic dissection
• chest pain in the ED
• EMedicine

• 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

• 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 alive 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

• incidence 5-10 per million pop. per year
• ~40-50 people die in Australia each year from aortic dissection - the far majority do prior to attending a hospital
• 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
  • fibromuscular dysplasia (FMD)
  • familial incidence
  • pregnancy (accounts for 50% of dissections in women under 40yrs)
  • coarctation of aorta - probably due to upper extremity hypertension
  • Turner syndrome
  • phaeochromocytoma
  • 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
      • see also blunt aortic injury
• risk factors in addition to above:
  • systemic hypertension (present in >2/3rds of pts, esp. if distal dissection)
  • polycystic kidneys
  • chronic steroid use or immunocompromise
  • vasculitis - esp. Takayasu arteritis, giant cell arteritis, and Behcet arteritis
  • lactylation of the mitochondrial ATP synthase subunit alpha (ATP5F1A) at the K531 site promotes the development and progression of AD by impairing mitochondrial function and inducing a phenotypic switch in vascular smooth muscle cells (VSMCs)³⁾

• 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)

• 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

• 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

• Type A:
  • involve ascending aorta
  • these are much more lethal & have a different Mx to Type B dissections
  • 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

• 90% have pain (if not present patient is either unconscious, elderly or has neurologic deficit that impairs pain perception such as a stroke):
  • usually abrupt, severe onset of sharp, stabbing, tearing, or ripping (but may be “crushing”), and pain may improve until a secondary progression of the dissection occurs (often in the next 24hrs) which then may be fatal
  • ascending aorta ⇒ ant. chest pain (71% of Type A dissections present with anterior pain)
  • arch aorta ⇒ pain in neck & jaw
  • descending aorta ⇒ inter-scapular 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
• rarely, may present with Ortner's syndrome and acute onset dysphagia or a choking sensation
  • see https://en.wikipedia.org/wiki/Ortner%27s_syndrome
• >75% have PH chronic hypertension
  • often poorly controlled
• late presentations involving distal aorta:
  • may present as epigastric pain with vomiting +/- fever, hypotension and raised inflammatory markers such as CRP > 100 followed by back pain as it further progresses

• generally pt is very apprehensive with tachycardia & may have 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
  • cardiac tamponade:
    • 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 interruption 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

• NNT.com's calculations

• see ADD - an aortic dissection risk assessment tool

• most are of little value in Dx although a D-Dimer pathology test is very sensitive but not specific
• C reactive protein (CRP) is often raised in those with delayed diagnosis

• early, small studies suggested a sensitivity > 95% but recent studies suggest sensitivity appears to be only ~ 82%⁴⁾ 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. ⁵⁾
• a negative D-Dimer appears to be sufficient to rule out dissection if the ADD score is 0 or 1.⁶⁾

• 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

• 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

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

• 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

• 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

• 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) ⁷⁾

• 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

• 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

• Tasmania Aug 2014 report - missed dissection on a non-contrast CT scan
• Victoria June 2014 - Western Hospital - failed to consider Dx? - need for education of clinical features and perhaps use of scoring tools
• NSW cases 2010 - death after stress test - dissection not considered in chest pain pathway, and ongoing pain should be C/I to stress testing (doc)