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Sanjiv SharmaAll India Institute of Medical Sciences
New Delhi
Imaging Algorithms in Acute Aortic Syndromes
Acute Aortic
SyndromeIMH PAU
Aortic Dissection
”characterised by aortic pain with a history of HT” Villacosta I, San Román JA. Acute aortic syndrome. Heart 2001;85:365-8
common denominator is disruption of aortic media with bleeding within the layers
Acute Aortic Syndrome
Acute Aortic Syndrome
• A tear or an ulcer allows blood to penetrate from aortic lumen into media or rupture of ‘vasa vasorum’
• Inflammatory response to blood in media further initiates necrosis & apoptosis leading to degeneration of elastic tissue, that can cause further aortic dilatation or rupture
Lack of diagnosis at initial evaluation: 42% of patients(Spittell PC, Mayo Clin Proc 1993; 68:642)
Early Accurate Diagnosis Is a Key to Survival AAS: A Medley of Great Mimickers
Predisposing Factors• Hypertension• Connective tissue disorder• Bicuspid aortic valve• Coarctation• Previous cardiac surgery• Recent percutaneous
instrumentation• Deceleration injuries• Cocaine abuse• Peri-partum period
Diagnosis of Acute Aortic Syndrome
• Rapid imaging essential to avoid delay in detecting potentially life-threatening complications
• Frequent combination of:* missed diagnosis* atypical presentation* time-dependent morbidity & mortality
• Selection of optimal imaging technique is critical for diagnosis & treatment planning
Goals of Imaging• Establish diagnosis & localize type• Anatomical features
* presence of absence of dissection* location, extent* Sites of entry & reentry * False lumen patency (partial or complete thrombosis)* Relation to branch vessels
• Complications of dissection a Type A
i Aortic regurgitation ii Coronary artery involvement iii Pericardial, mediastinal or pleural effusion
b Aortic rupture- contained or frank c Branch vessel involvement d Malperfusion
Imaging Techniques
• Chest Radiograph
• ECHO
• CT Angiography
• MRI
• Catheter angiography
Factors Determining Choice of Imaging Technique
• Hemodynamic stability• Renal function/GFR• Complication-
presence/absence(based on clinical assessment)
• Availability of imaging techniques
• Local expertise
Chest Radiograph • Widening mediastinum (80% to
90% of cases (83%, type A; 72%, type B)
• Obliteration of aortic knob • Displaced intimal calcification (>5
mm) -calcium sign • Displacement of trachea to right• Distortion of left main-stem
bronchus• Pleural effusion (more common left
sided)• Cardiomegaly• Normal in 12% to 15% of casesChallenge- findings often nonspecific;In appropriate clinical setting, chest radiograph can be very helpful
Echocardiography for Acute Aortic Syndrome
• TTE provides vital prognostic information* new-onset aortic insufficiency* pericardial effusion* visualization of proximal dissection* LV function & wall motion
• Portable, avoids transport of a critically ill patient; use in operating theatre
• TEE improves diagnostic accuracy• European Cooperative Study Group, IRAD -
99% sensitivity, 89% specificity, 89% PPV & 99% NPV
• Adjunctive use of colour Doppler- * confirm blood flow in true & false lumen * identify communication sites* see dynamic side-branch obstruction
• Limited by:* operator dependence * insufficient anatomic detail for EVR
MDCT for Diagnosis & Treatment Planning
• Standard of Care today for optimal evaluation
• Sensitivity- 85-98%, Specificity- 100%, NPV-85-96%, PPV-100%
• ECG gating can eliminate pulsation artifacts
• Establish diagnosis, identify type as well as complications
• Very useful for treatment planning (surgical or endovascular)
• Risk of radiation & iodinated contrast
MRI for diagnosis of Acute Aortic Syndrome
• Complementary rather than competing imaging modality for thoracic aorta
• Advantages- No radiation- No use of iodinated contrast
• Disadvantages- Limited availability- Long acquisition time- Gadolinium contrast caution in renal
impairment
MRI for Acute Aortic Syndrome• Sensitivity- 98%, specificity-
98% • Capable of multi-planar
imaging with 3-D reconstruction
• Cine MRI visualize blood flow, differentiating slow flow and clot and AR
• MRA can identify all complications- AR, pericardial effusion & branch vessel morphology
Little applicability in acute settings!Challenges of speed & clinical condition
Catheter Angiography for Diagnosis
• Diagnostic accuracy 90-95%• Identify intimal flap, true and
false lumen• Thickened wall (thrombosed
false lumen)• AR, branch vessel
involvement• 5-10% false negative rate
thrombosed false lumen simultaneous opacification of
both lumens misses IMH
• Risks of procedure
Has no place in the diagnostic algorithm if orthogonal imaging techniques are available
Neurologic Manifestations
• May dominate clinical presentation
• Neurologic syndromes include:• Persistent or transient
ischemic stroke• Spinal cord ischemia• Ischemic neuropathy• Hypoxic encephalopathy
Syncope
• Reported in up to15% of patients in IRAD
• Indicate development of dangerous complications
• Acute hypotension - Cardiac tamponade (10% of acute type A dissections) or aortic rupture
• Cerebral vessel obstruction or activation of cerebral baro receptors
Vascular insufficiency
• Renal artery - 5% to 10% • Renal ischemia,
infarction, renal insufficiency or refractory hypertension
• Mesenteric ischemia or infarction in 5%
• Extension to iliac arteries -acute limb ischemia
Acute Myocardial Infarction
• Flap causing mal-perfusion of coronary artery
• Occurs in 1-7% of acute type A dissections
• RCA is most commonly involved
Pleural & pericardial effusion
• Left-sided pleural effusion
• Usually related to inflammatory response
• Acute hemothorax
Intramural Hematoma
• Hemorrhage of vasa vasorum in medial layer of aorta or hematoma arises from microscopic tears in aortic intima
• Most (50-85%) are located in descending aorta
• Association with hypertension• 10-20% can have an acute aortic
syndrome• Common in older patients• Clinical picture of dissection
Markers of Prognosis- Location, thickness & presence of PAU
Evolution of IMH
• Complete resolution (10-30%)• Convert to classic dissection (3-14% of
descending aorta & in 11-88% of ascending aorta)
• Aorta may enlarge & develop into an aneurysm
Penetrating Aortic Ulcer• Atherosclerotic lesion penetrates
internal elastic lamina into media• Associated with variable degree of
IMH• May lead to pseudo aneurysm,
rupture, or late aneurysm• 2-8% of acute aortic syndrome• Acute chest or back pain, similar to
dissection• More common in descending aorta
(61.2%), Abdominal aorta (29.7%) , Arch of aorta (6.8%)
• 25% of PAUs are found incidentally
When should you intervene in Penetrating Aortic Ulcer?
• Ascending aorta location • Interval development of
hemorrhage• Peri-aortic hematoma• Expanding pseudo aneurysm
or rupture• Increasing aortic wall
thickness• Ulcer crater >20 mm in
diameter or >10 mm in depth• Increasing pleural effusion
Imaging algorithmAcute aortic syndrome
(Clinical & Chest Radiograph)
Window inadequate or signs of asc ao involvement
TTE
MDCT angiography(non-contrast f/b contrast scan)ORMRI with CE-MRA
Stable patient
Patient in shock
MDCT angiography(non-contrast f/b contrast scan)
TEE
TEE Unavailable or Imaging inadequate
Normal
?Type B
MDCT angiography(non-contrast f/b contrast scan)
Unstable patient (no shock)