Aortic Dissection

Aortic Dissection

• Jason S. Finkelstein, M.D.

• Cardiology Fellow

• Tulane University

• 8/11/03

Overview

• Incidence of aortic dissection is at least 2000 new cases per year

• Peak incidence is in the sixth to seventh decade

• Men are affected twice as commonly as women

• Mortality in the first 48 hours is 1% per hour

• Early diagnosis is essential

Pathophysiology

• The chief predisposing factor is degeneration of collagen and elastin in the aortic intima media

• Blood passes through the tear into the aortic media, separating the media from the intima and creating a false lumen

• Dissection can occur both distal and proximal to the tear

Classification

• Debakey system

• Type I
• Originates in the ascending aorta, propagates to the aortic arch and beyond it distally
• Type II
• Confined to the ascending aorta
• Type III
• Confined to the descending aorta, and extends distally, or rarely retrograde into the aortic arch

Classification

• The Stanford system

• Type A
• All dissections involving the ascending aorta
• Type B
• All other dissections regardless of the site of the primary intimal tear
• Ascending aortic dissections are twice as common as descending

Predisposing factors

• Age, 60-80 yrs old

• Long standing history of hypertension

• 80% of cases have co-existing HTN

• Takayasu’s arteritis

• Giant cell arteritis

• Syphilis

• Collagen disorders

• Marfan syndrome (6-9% of aortic dissections)
• Ehlers-Danlos syndrome

Other Risk Factors

• Congenital Cardiac Anomalies

• Bicuspid aortic valve (7-14% of cases)
• Coarctation of the aorta

• Cocaine

• Abrupt HTN, due to catecholamine release

• Trauma

• Pregnancy (50% of dissections in women <40 yrs)

• Iatrogenic (cardiac cath, IABP, cardiac surgery, s/p valve replacement)

Clinical Symptoms

• Severe, sharp, “tearing” posterior chest pain or back pain (occurs in 74-90% of pts)

• Pain may be associated with syncope, CVA, MI, or CHF
• Painless dissection relatively uncommon

• Chest pain is more common with Type A dissections

• Back or abdominal pain is more common with Type B dissections

Physical Exam

• Pulse deficit

• Weak or absent carotid, brachial, or femoral pulses
• these patients have a higher rate of mortality

• Acute Aortic Insufficiency

• Diastolic decrescendo murmur
• Best heard along the right sternal border

Clinical signs

• Acute MI

• RCA most commonly involved

• Cardiac tamponade

• Pleural effusions

• Hypertension or hypotension

• Hemothorax

• Variation in BP between the arms (>30mmHg)

• Neurologic deficits

• Stroke or decreased consciousness

Clinical Signs

• Involvement of the descending aorta

• Splanchnic ischemia
• Renal insufficiency
• Lower extremity ischemia
• Spinal cord ischemia

Diagnosis

• Generally suspected from the history and PE

• In a recent study in 2000, 96% of acute dissection patients could be identified based upon a combination of three clinical features

• Immediate onset of chest pain
• Mediastinal widening on CXR
• A variation in pulse and/or blood pressure (>20 mmHg difference between R & L arm

• Incidence >83% when any combination of all three variables occurred

Differential Diagnosis

• Acute Coronary Syndrome

• Pericarditis

• Pulmonary embolus

• Pleuritis

• Cholecystitis

• Perforating ulcer

Diagnostic Tests

• EKG

• Absence of EKG changes usually helps distinguish dissection from angina
• Usually non-specific ST-T wave changes seen

• CXR

• Cardiac Enzymes

Chest X-Ray

• May show widening of the aorta with ascending aorta dissections

• Present in 63 % of patients with Type A dissections

Diagnostic Imaging

• Not performed until the patient is medically stable

• Has been a dramatic shift from invasive to non-invasive diagnostic strategy

• Spiral CT scan

• TEE

• MRI

• Angiography

Imaging

• Can identify aortic dissection and other features such as:

• Involvement of the ascending aorta
• Extent of dissection
• Thrombus in the false lumen
• Branch vessel or coronary artery involvement
• Aortic insufficiency
• Pericardial effusion with or without tamponade
• Sites of entry and re-entry

Angiography

• First definitive test for aortic dissection

• Traditionally considered “the gold standard”

• Involves injection of contrast media into the aorta

• Identifies the site of the dissection
• Major branches of the aorta
• Communication site between true & false lumen
• Can detect thrombus in the false lumen

• Disadvantages

• Not very practical in critically ill patients
• Nephrotoxic contrast
• Risks of an invasive procedure

Spiral CT

• Sensitivity 83%

• Specificity 90 - 100%

• Two distinct lumens with a visible intimal flap can be identified

• Advantages

• Noninvasive
• Readily available at most hospitals on an emergency basis
• Can differentiate dissection from other causes of aortic widening (tumor, periaortic hematoma, fat)

• Disadvantages

• Sensitivity lower than TEE and MRI
• Intimal flap is seen < 75% of cases
• Nephrotoxic contrast is required
• Cannot reliably detect AI, or delineate branch vessels

TTE

• First used to diagnose aortic dissections in the ’70s

• Sensitivity 59-85%, specificity 63-96%

• Image quality limited by obesity, lung disease, and chest wall deformities

TEE

• Sensitivity 98% Specificity 95%

• Advantages

• Close proximity of the esophagus to the thoracic aorta
• Portable procedure
• Yields diagnosis in < 5 minutes
• Useful in patients too unstable for MRI
• True and false lumens can be identified
• Thrombosis, pericardial effusion, AI, and proximal coronary arteries can be readily visualized

TEE

• Lower specificity attributed to reverberations atherosclerotic vessels or calcified aortic disease producing echo images that resemble an aortic flap

• Disadvantages

• Contraindicated in patients with esophageal varices, tumors, or strictures
• Potential complications: bradycardia, hypotension, bronchospasm

MRI

• Most accurate noninvasive for evaluating the thoracic aorta

• Sensitivity 98%

• Specificity 98%

• Advantages

• Safe
• Can visualize the whole extent of the aorta in multiple planes
• Ability to assess branch vessels, AI, and pericardial effusion
• No contrast or radiation

• Disadvantages

• Not readily available on an emergency basis
• Time consuming
• Limited applicability in pts with pacemakers or metallic clips

Conclusions

• Conventional TTE is of limited diagnostic value in assessment of the thoracic aorta

• Both TEE and MRI have excellent sensitivity, however MRI is more specific

• MRI is the study of choice for stable patients

• TEE is the study of choice for unstable patients

Treatment

• Acute dissections involving the ascending aorta are considered surgical emergencies

• Dissections confined to the descending aorta are treated medically

• Unless patient demonstrates continued hemorrhage into the pleural or retroperitoneal space

Surgical Options

• Excision of the intimal tear

• Obliteration of entry into the false lumen proximally

• Reconstitution of the aorta with interposition of a synthetic vascular graft

Type A Dissections

• Operative mortality varies from 7-35%

• 27% post-op mortality

• Patients who died had a higher rate of in-hospital complications such as strokes, renal failure, limb ischemia, & mesenteric ischemia

Poor prognostic factors

• Hypotension or shock

• Renal failure

• Age> 70 yrs

• Pulse deficit

• Prior MI

• Underlying pulmonary disease

• Preoperative neurologic impairment

• Renal and/or visceral ischemia

• Abnormal EKG, particularly ST elevation

Medical therapy

• Reduce systolic BP to 100 to 120 mmHg or the lowest level that is tolerated

• IV Beta blockers

• Propanolol (1-10 mg load, 3mg/hr)
• Labetalol (20 mg bolus, 0.5 to 2 mg/min)

• If SBP remains >100mmHg, nitroprusside should be added

• Do not use without beta blockade
• Avoid hydralazine

• Surgical intervention for Type B dissections reserved for patients with a complicated course

Long Term Outcome

• Type A

• Survival at 5 yrs – 68%
• Survival at 10 yrs – 52 %

• Type B

• 5 yrs – 60 - 80%
• 10 yrs – 40 – 80%
• Spontaneous healing of dissection is uncommon

Long-Term Management

• Medical therapy

• Oral Beta-blockers (reduces aortic wall stress)
• Keep BP < 135/80 mmHg (combination therapy)
• Avoidance of strenuous physical activity

• Serial imaging

• Thoracic MR scan prior to discharge
• f/u scans at 3, 6, and 12 months
• Subsequent screening studies done every 1-2 yrs if no evidence of progression