Non-Invasive Conference:Aortic Dissection

Ali R. Rahimi, MD MPH

September 24, 2008

Anatomy

Aortic Dissection

“a splitting of the layers of the aortic wall (within the media), permitting longitudinal propagation of a blood-filled space within the aortic wall”

Most common cause of death related to the human aorta

Incidence 2.6 to 3.5 per 100,000 person-years

65% men with mean age of 63 years

Pathophysiology

Degeneration of aortic media, or cystic medial necrosis, is prerequisite for nontraumatic dissection

Primary rupture of intima with secondary dissection of the media vs. hemorrhage within the media and subsequent rupture of overlying intima

Propagation can occur both distal and proximal

Risk Factors

Systemic hypertension (72%)

Atherosclerosis (31%)

Pre-existing aortic aneurysm (13% known) more common < 40 yo (19%)

Vasculitis (giant cell arteritis, Takayasu arteritis, rheumatoid arthritis, syphilitic aortitis)

Risk Factors

Disorders of collagen (eg, *Marfan syndrome, Ehlers-Danlos syndrome, annuloaortic ectasia) *Present in 50% of those < 40 yo vs. 2% of older patients

Bicuspid aortic valve Present in 9% < 40 yo vs. 1% over age 40 Enlargement of aortic root and/or ascending aorta

Aortic coarctation, Turner Syndrome, CABG (0.04%), Prior AVR, Cardiac Cath (2%), Trauma (deceleration injury), Weight lifting, Crack cocaine

Ascending aortic dissections ~ 2x as common Right lateral wall of ascending aorta most common site Aortic arch involvement ~ 30%

Variants

Class I - classic separation of intima/media and dual lumens; flap between true and false aneurysm and clot in false lumen;

Class II - intramural hematoma with separation of intima/media but no tear or flap; Class III - limited intimal tear without hematoma and eccentric bulge at tear site; Class IV - atherosclerotic ulcer penetrating to adventitia with surrounding hematoma; Class V- iatrogenic or traumatic dissection

Clinical Presentation

Severe, sharp or "tearing" posterior chest or back pain (distal to L subclavian) or anterior CP (ascending dissection)

Isolation or with syncope, CVA, MI, CHF, …

HTN more common in type B dissection (70% vs. 36%)

Pulse deficit in 19-30% with an acute type A dissection vs. 9-21% with a type B dissection

Clinical Finding Artery or Structure

Aortic insufficiency or CHF Aortic valve

AMI Coronary artery (right)

Tamponade Pericardium

Hemothorax Thorax

CVA or Syncope Brachiocephalic, CC, Left subclavian

UE pulselesness, low BP, pain Subclavian

Paraplegia Intercostal

LE pain, pulselessness, weakness Common iliac

Abdominal pain, mesenteric ischemia Celiac or mesenteric

Back or flank pain; ARF Renal artery

Horner syndrome Superior cervical sympathetic ganglion

Differential Diagnosis

Acute Coronary Syndrome Pericarditis Pulmonary embolus Aortic regurgitation without dissection Aortic aneurysm without dissection Musculoskeletal pain Mediastinal tumors Pleuritis Cholecystitis Atherosclerotic or cholesterol embolism Peptic ulcer disease or perforating ulcer Acute pancreatitis

Diagnosis

Clinical Prediction of Aortic Dissection

Study of 250 pts with acute chest and/or back pain (128 with AD) found 96% with acute AD identified using 3 clinical features:

Abrupt onset of thoracic or abdominal pain with a sharp, tearing and/or ripping character

Mediastinal and/or aortic widening on chest radiograph Variation in pulse (absence of a proximal extremity or carotid pulse)

and/or blood pressure (>20 mmHg difference in the right and left arm)

Any 2 out of 3 variables (77% of dissections): ≥83%

Additional imaging studies obtained in 98% of pts due to limited sensitivity of CXR, especially in type B dissections

Chest X-Ray

Type A 63% with mediastinal widening, 11% with no abnormality

Type B 56% with mediastinal widening, 16% with no abnormality

Electrocardiogram

31% normal

42% non-specific ST and T wave changes

15% ischemic changes

5% changes c/w AMI

Advanced Imaging Modalities

Aortic Dissection

Involvement of the ascending aorta The extent of dissection and the sites of entry and

reentry Thrombus in the false lumen Branch vessel or coronary artery involvement Aortic insufficiency Pericardial effusion

Advanced Imaging Modalities

Based on year 2000 IRAD:

mean 1.83 studies per patient 61% CT 33% Echocardiography 4% Aortography 2% MRI

ESC Guidelines for Diagnostic Imaging of Acute Aortic Dissection

Class I - TTE followed by TEE

Class II – CT, CTA to define anatomy

Class IIa – CTA in stable pts, MRI in stable pts, Intravascular US

Class IIb - CT if detection of tears is crucial, CTA in unstable pts, intravascular US to guide intervention

Class III – MRI in hemodynamically unstable patients, routine pre-op CTA

ESC Guidelines for Diagnostic Imaging of Chronic Aortic Dissection

Class I – MRI

Class IIa – TTE, TEE, CTA

CT Scan

CT Scan

CT Scan

CT Scan Sensitivity 83-98% Specificity 87-100% Advantages:

availability at most hospitals ID of intraluminal thrombus and pericardial effusion

Disadvantages: Intimal flap seen < 75% of cases and site of entry is rarely

identified Potentially nephrotoxic iodinated contrast Unable to assess for aortic insufficiency

Accuracy of CT is improved with spiral CT and electron beam or multidetector CT

Spiral CT may be more accurate than MRI or TEE in the detection of aortic arch vessel involvement Limitation: Without ECG gating simulate artifact ~ aortic

dissection

TTE

TTE

TTE

TTE

TTE

TTE

TTE

Limited utility for evaluation of the thoracic aorta for dissection unable to adequately visualize distal ascending, transverse, and

descending aorta in a substantial majority of patients

Intimal flap in the proximal aorta may be seen, though the sensitivity and specificity of TTE are inferior compared to CT, MRI, and TEE

Most useful for assessment of cardiac complications of dissection, including AI, pericardial effusion/tamponade, and regional LV dysfunction

TEE

TEE

TEE

TEE

TEE

TEE

TEE

TEE Advantages

sensitivity 97 – 99% close proximity of esophagus to thoracic aorta and absence of an

intervening lung or chest wall portable procedure diagnosis within minutes useful in patients too unstable for CT or MRI intimal dissection flaps can be identified with high spatial resolution true and false lumens can be identified thrombosis in the false lumen, pericardial effusion, aortic

regurgitation, and the proximal coronary arteries can be visualized 135º long axis view can define severity and mechanism of aortic

regurgitation that complicates acute type A dissections

TEE

Disadvantages

Specificity as low as 77-85% false-positive findings in the ascending aorta artifacts can be detected by addition of M-mode imaging,

increasing specificity to almost 100%

Requires sedation and esophageal intubation

TEE requires availability of experienced operators (both physicians and technicians) to assure accurate results

Hagan, Etc, JAMA 2000 283:897

30 Day Mortality Rates for Acute Aortic Dissection

Mechanical Composite Root Repair with and w/o Hemiarch Repair

Homograft Repair

Porcine BioRoot Replacement

Valve Sparing Replacement

Aortic Dissection Repair:Teflon Felt as Neomedia

Endovascular Aortic Stent Grafts

Endovascular Aortic Stents

References

Hurst the Heart, 11th Edition Manning, W. UpToDate Online 16.2.

Clinical manifestations and diagnosis of aortic dissection.