Aortic Dissection

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Aortic Dissection

• Jason S. Finkelstein, M.D.
• Cardiology Fellow
• Tulane University
• 8/11/03

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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

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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

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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

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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

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Predisposing factors

• Age, 60-80 yrs old
• Long standing history of hypertension
• 80 of cases have co-existing HTN
• Takayasus arteritis
• Giant cell arteritis
• Syphilis
• Collagen disorders
• Marfan syndrome (6-9 of aortic dissections)
• Ehlers-Danlos syndrome

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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 lt40 yrs)
• Iatrogenic (cardiac cath, IABP, cardiac surgery,
  s/p valve replacement)

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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

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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

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Clinical signs

• Acute MI
• RCA most commonly involved
• Cardiac tamponade
• Pleural effusions
• Hypertension or hypotension
• Hemothorax
• Variation in BP between the arms (gt30mmHg)
• Neurologic deficits
• Stroke or decreased consciousness

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Clinical Signs

• Involvement of the descending aorta
• Splanchnic ischemia
• Renal insufficiency
• Lower extremity ischemia
• Spinal cord ischemia

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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 (gt20
  mmHg difference between R L arm
• Incidence gt83 when any combination of all three
  variables occurred

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Differential Diagnosis

• Acute Coronary Syndrome
• Pericarditis
• Pulmonary embolus
• Pleuritis
• Cholecystitis
• Perforating ulcer

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Diagnostic Tests

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

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Chest X-Ray

• May show widening of the aorta with ascending
  aorta dissections
• Present in 63 of patients with Type A
  dissections

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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

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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

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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

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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 lt 75 of cases
• Nephrotoxic contrast is required
• Cannot reliably detect AI, or delineate branch
  vessels

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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

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TEE

• Sensitivity 98 Specificity 95
• Advantages
• Close proximity of the esophagus to the thoracic
  aorta
• Portable procedure
• Yields diagnosis in lt 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

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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

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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

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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

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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

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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

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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

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Poor prognostic factors

• Hypotension or shock
• Renal failure
• Agegt 70 yrs
• Pulse deficit
• Prior MI
• Underlying pulmonary disease
• Preoperative neurologic impairment
• Renal and/or visceral ischemia
• Abnormal EKG, particularly ST elevation

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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 gt100mmHg, 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

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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

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Long-Term Management

• Medical therapy
• Oral Beta-blockers (reduces aortic wall stress)
• Keep BP lt 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