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
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)
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 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
history:
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
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
strongly consider dissection in:
ANY patient with SUDDEN onset severe chest pain (but especially if during straining/lifting or in the elderly) which is slowly IMPROVING, especially if PH hypertension or pain radiates to jaw, back or abdomen even if there is a mild troponin rise suggesting a NSTEMI!
ANY patient with new severe pain PLUS new neurology in the absence of trauma
examination:
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
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)
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
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
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.