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)