Aortic Dissection

Epidemiology

Gender: Most common in males by factor of 2-3 to 1
Age: 40-80 years old
Incidence: 6000-10,000 per year in US
1. Rare: Accounts for 0.09% of Chest Pain presentations in U.S.

Pathophysiology

Aortic wall is composed of three layers: Intima (inner), media and adventitia (outer)
Aortic Dissection has a very different mechanism than Abdominal Aortic Aneurysm
1. AAA is caused by atherosclerosis and involves all three layers of aorta wall
2. Aortic Dissection is caused by Hypertension and involves only the innermost layer (intima)
Intimal tear precedes dissection

Precautions

Keep Aortic Dissection in the Chest Pain differential diagnosis
Aortic Dissection may present in similar fashion to Acute Coronary Syndrome, Pulmonary Embolism, Pericarditis
1. However, empiric antiplatelets and Anticoagulants can result in worse outcomes for dissection
Atypical presentations are very common with a wide variety of findings that mimic other conditions (Malperfusion Syndromes)
1. Transient Global Amnesia or Altered Mental Status
2. Cerebrovascular Accident (Carotid Artery malperfusion)
3. Painless lower extremity weakness or Paraplegia (e.g. spinal artery malperfusion)
4. Cold painful leg (iliac artery malperfusion)
5. Abdominal Pain or Mesenteric Ischemia (superior Mesenteric Artery malperfusion)
6. New onset CHF or ST Elevation MI (Coronary Artery malperfusion)
7. Acute Kidney Injury or Renal Infarction (renal artery malperfusion)
Older adults have less typical presentations
1. See Chest Pain in Older Adults
2. Insidious onset of Chest Pain is more common in older adults than the sudden Chest Pain in younger adults
3. Tearing, ripping or sharp Chest Pain is often absent in older adults
4. Hypotension is a more common presentation in older adults

Risk Factors

Male gender (>2:1 ratio)
Pregnancy
1. Incidence increases during pregnancy and peaks in third trimester and Postpartum Period
2. Still rare in pregnancy without other predisposing factors (e.g. Collagen vascular disease, Hypertension)
3. Stanford Type A Dissection is more common type
Cocaine Abuse or other Sympathomimetics
Chronic Hypertension (present in 70-90% of cases, esp uncontolled)
Giant Cell Arteritis
Family History of aortic disease
Pre-existing aorta structural abnormalities
1. Bicuspid aortic valve
2. Aortic Coarctation
3. Thoracic Aortic Aneurysm
4. Prior Aortic Dissection history
5. Cardiovascular procedures (especially recent)
  1. Cardiac or aorta surgery
  2. Cardiac catheterization
Connective Tissue Disease (presentation at younger ages, <40 years old)
1. Marfan's Syndrome
2. Ehlers-Danlos Syndrome
Other risk factors
1. Hyperlipidemia
2. Tobacco Abuse
3. Weight Lifting
4. Pheochromocytoma
5. Polycystic renal disease
6. Chronic Corticosteroid use
7. Chronic Immunosuppressant use
8. Aortic wall infections

Types
Standford Classification

Type A (60-65%, Debakey Type I and II)
1. Ascending Aorta and/or aortic arch (dissection may extend intracardiac)
2. In a Debakey Type II, the Aortic Dissection is limited to the aortic arch
Type B (30-35%, Debakey Type III)
1. Descending Aorta (after origin of subclavian artery)

Symptoms

Chest Pain (94% of patients)
1. Severe, sudden tearing Sensation in the chest, back or Abdomen (may radiate into legs)
2. Aortic Dissection pain radiates to back or Abdomen
  1. Myocardial Infarction rarely radiates like this
3. Aortic Dissection pain is most severe at onset
  1. Myocardial Infarction pain is typically crescendo in nature
Neurovascular symptoms
1. Cerebrovascular Accident
  1. Visual deficit
  2. Hemiparesis
  3. Bilateral paresis
2. Syncope
3. Extremity Paresthesias

Symptoms
Test Sensitivity at presentation with Aortic Dissection (based on IRAD Data)

Classic Triad (100% Test Specificity if present, but most cases are atypical and do not have all 3 findings)
1. Severe abrupt onset, ripping or tearing Chest Pain that radiates to back AND
2. Pulse deficit or difference in upper extremity Blood Pressure >20 mmHg AND
3. Mediastinal Widening or aortic knob widening on Chest XRay
Timing
1. Sudden onset: 85%
Severity
1. Severe pain: 90%
Characteristics
1. Pain: 95%
  1. Type A: 94%
  2. Type B: 98%
2. Sharp pain: 64%
3. Tearing/ripping: 50%
  1. Type A: 49%
  2. Type B: 52%
Distribution: Typically involves both above and below the diaphragm
1. Anterior Chest Pain: 61%
  1. Type A: 71%
  2. Type B: 44%
2. Back pain: 53%
  1. Type A: 46%
  2. Type B: 64%
3. Abdominal Pain: 35%
  1. Type A: 22%
  2. Type B: 42%
4. Migrating pain: 17%
  1. Type A: 15%
  2. Type B: 19%
Associated Findings
1. Syncope: 9%
  1. Type A: 13%
  2. Type B: 4%

Signs

Blood Pressure at presentation (based on IRADS results)
1. Hypertensive SBP>150: 49%
  1. Type A: 36%
  2. Type B: 70%
2. Normotensive SBP 100-150: 35%
3. Hypotensive or shock SBP: 16%
  1. Type A: 25%
  2. Type B: 4%
4. Blood Pressure differential between sides
  1. Poor sensitivity and Specificity for Aortic Dissection
  2. Up to 20% of normal patients have a Blood Pressure differential of at least 20 mmHg
Pulse on presentation
1. Pulse deficit: 15-30%
  1. Type A Dissection: Two thirds of those with pulse deficit
  2. Type B Dissection: One third of those with pulse deficit
  3. Positive Likelihood Ratio when associated with acute Chest Pain or back pain: 5.3 to 5.7
    1. Von Kodolitsch (2000) Arch Intern Med 160(19): 2977-82 [PubMed]
2. Palpable pulse differential
  1. Less prominent pulse (e.g. radial pulse) on one side compared with the other
Aortic Murmur: 30%
1. Aortic Regurgitation murmur suggests a Type A dissection with intracardiac involvement
2. Overall, new murmurs are found in 50% of Aortic Dissection patients
Cardiac Tamponade (5% of Type A Dissections)
Findings associated with dissection of Hematoma
1. Altered Mental Status (12% of Type A Dissections)
2. Cerebrovascular Accident (8% of Type A Dissections)
3. Focal neurologic deficit (e.g. Hemiplegia)
4. Pulse deficits
5. Aortic Insufficiency
6. Mesenteric Ischemia
7. Acute Kidney Injury
8. Paraplegia (spinal artery Occlusion)

Labs

Basic metabolic panel
1. Acute Renal Failure may occur depending on level of dissection
D-Dimer
1. Consider when evaluating differential diagnosis
2. Normal D-Dimer (up to 10% False Negative Rate) does not exclude Thoracic Dissection
Serum Troponin
1. Elevated in Acute Coronary Syndrome, Aortic Regurgitation

Diagnostics

Electrocardiogram
1. Test Sensitivity: 69%
2. Test Specificity: Low (non-diagnostic)
3. Left Ventricular Hypertrophy
4. Myocardial Ischemia
5. Myocardial Infarction
Emergency Echocardiography (bedside)
1. Evaluate for Pericardial Effusion
Acute Aortic Dissection Score (ADD-RS)
1. https://www.mdcalc.com/aortic-dissection-detection-risk-score-add-rs
2. ADD-RS score criteria (1 point for each of the following present)
  1. Any high risk condition (e.g. Marfan Syndrome, known aortic valve disease)
  2. Any high risk pain feature (abrupt, severe, tearing Chest Pain, Abdominal Pain, back pain)
  3. Any high risk exam feature (e.g. pulse or Blood Pressure differences, focal neurologic deficits)
3. ADD-RS score >1 or D-Dimer positive is an indication for CT Angiogram
4. References
  1. Nazerian (2018) Circulation 137(3):250-8 +PMID:29030346 [PubMed]

Imaging

Aortic Angiography (gold standard)
1. Test Sensitivity: 90-98%
2. Test Specificity: 95-98%
CT Angiography Chest (Chest CTA) - preferred first line study
1. Similar efficacy to Transesophageal Echocardiogram (TEE) or MRA
2. Test Sensitivity: 100% with new generation CT (older studies quoted 94%)
3. Test Specificity: 98% with new generation CT (older studies quoted 90%)
4. Risk of cardiac motion artifacts near the aortic root
  1. EKG Gating can reduce this artifact
Transesophageal Echocardiogram
1. Limited availability at non-tertiary hospitals
2. Test Sensitivity: 97%
3. Test Specificity: 75-90%
Transthoracic Echocardiogram
1. Test Sensitivity: 77-80%
2. Test Specificity: 74-96%
3. Not recommended to rule-out Aortic Dissection (low Test Sensitivity)
4. Does identify Aortic Dissection complications (Cardiac Tamponade)
5. Bedside Ultrasound evaluation on Parasternal Long-Axis Echocardiogram View (PLAX View)
  1. Aorta Diameter Measurement on PLAX View (for Aortic Dissection)
  2. Measure the maximal distance between anterior and posterior walls of aorta
    1. Probe should be perpendicular to the two aorta walls
    2. Distance >4 cm is concerning for Aortic Dissection
    3. Other suggestive findings: Pericardial Effusion, flap within the aorta
MRA Chest
1. Not recommended as an emergency evaluation (may be indicated in some stable patients)
2. May be considered when iodinated contrast or CTA is contraindicated
3. Test Sensitivity: 98%
4. Test Specificity: 98%
Chest XRay
1. Test Sensitivity: 64-71% (up to 90% for a completely otherwise normal Chest XRay)
2. Test Specificity: Low (non-diagnostic)
3. Unlikely to demonstrate anything more than intrathoracic catastrophe
4. Mediastinal Widening (progressive), aortic knob widening
5. Double density aorta (lines define margins of true and false lumens)
6. Tracheal, Bronchial or esophageal deviation to the right
7. Pleural Effusion

Complications

Neurologic deficits
1. Cerebrovascular Accident
Unequal perfusion
1. Unequal pulses
2. Unequal extremity Blood Pressures
Myocardial Ischemia or Myocardial Infarction
1. Proximal Aortic Dissection involves the coronary arteries in 3% of cases
2. Right Coronary Artery is most often involved (inferior ST Elevation)
Aortic Regurgitation (with Cardiogenic Shock)
Aortic valve rupture
Cardiac Tamponade

Management
Acute Management

Consult Vascular Surgeon early on suspicion of Aortic Dissection
1. See Surgical Management as below
Lower Blood Pressure (in addition to Heart Rate lowering)
1. Goals to reduce risk of further dissection (confirm goal levels with accepting vascular surgeon)
  1. Blood Pressure goal: <120 mmHg (based on consensus expert opinion)
  2. Heart Rate goal: <60 bpm (based on consensus expert opinion)
2. First-Line Agents: Beta Blockers
  1. Esmolol
  2. Labetalol 20-40 mg incremental boluses IV
    1. Consider while awaiting CT imaging and diagnosis
  3. Metoprolol
3. Second-Line Agents: Calcium Channel Blockers
  1. Nicardipine
  2. Clevidipine
4. Third-line Agents (Refractory Hypertension after rate control)
  1. ACE Inhibitors (e.g. IV Enaprilat)
  2. Vasodilators (e.g. Nitroprusside 0.5-10 ug/kg/min IV)
    1. Contraindicated before Heart Rate is controlled (risk of reflex Tachycardia)
5. Adjunctive measures
  1. Decreasing pain will decrease Blood Pressure
6. Older agents that have largely been replaced
  1. Trimethaphan 1-4 mg/min IV
Pain control
1. IV Opioids
2. Avoid IV NSAIDs
Definitive Management
1. Proximal Aortic Dissection (Type A)
  1. Mortality 1-2% per hour
  2. Emergent surgical management
2. Distal Aortic Dissection (Type B)
  1. Initial medical management (including Blood Pressure control as above)
  2. Surgery will be needed in 20-33% of cases
    1. Acute renal artery Occlusion
    2. Superior Mesenteric Artery Occlusion
    3. Acute iliac Occlusion
Hypotension
1. Type and crossmatch and consider transfusion
2. Consider Aortic Dissection-related causes (Bedside Ultrasound)
  1. Cardiac Tamponade
  2. Acute valvulopathy
  3. Myocardial Infarction with Cardiogenic Shock
  4. Ruptured aorta with Hemothorax
  5. Falsely depressed Blood Pressure (dissection causes decreased perfusion to the arm with BP cuff)

Management
Surgical

Indications for immediate, emergent surgical repair (even if neurologic deficits, coma, shock, advanced age)
1. All Stanford Type A Aortic Dissection
2. Aortic Dissection with Hypotension
3. Complicated Stanford Type B Aortic Dissection
  1. Aortic Dissection with Acute Limb Ischemia, Mesenteric Ischemia, spinal ischemia
  2. Refractory hemodynamic instability
  3. Aortic Rupture
  4. Rapidly increasing aortic size
Repair Types
1. Open Repair
  1. Indicated in all Type A Aortic Dissections
  2. Indicated in Connective Tissue Disorders (Marfan Syndrome, Ehlers-Danlos Syndrome)
2. Thoracic Endovascular Aortic Repair or TEVAR
  1. Indicated in Type B, descending Aortic Dissection repair
  2. Endovascular stent graft inserted over proximal intimal tear
  3. Redirects Blood Flow through the true lumen
Efficacy
1. Type A Dissection mortality reduced >30%
2. Aortic root repair often preserve native aortic valve in acute Aortic Regurgitation
Complications
1. Open Repair
  1. Post-operative stroke: 15%
  2. Perioperative mortality: 25%
  3. Acute Renal Failure
  4. Mesenteric Ischemia
  5. Spinal cord ischemia
2. Endovascular Repair (TEVAR)
  1. Overall Mortality: 6-8%
  2. Lower rates of spinal cord ischemia than open repair

Prognosis

High mortality: 27% even under ideal conditions
Proximal Aortic Dissection (Type A)
1. Mortality increases 1-3% per hour from onset (first 48 hours)
2. Mortality with medical therapy: 50%
3. Mortality with surgical management: 7-36%
Distal Aortic Dissection (Type B)
1. Mortality 10%

References

Mattu and Swaminathan in Herbert (2019) EM:Rap 19(1): 6-8
Mattu and Swaminathan in Herbert (2021) EM:Rap 21(3): 13-4
Rooke (2017) Vascular Medicine, Mayo Clinical Reviews, Rochester, MN
Dachs (2012) Board Review Express, San Jose
Jhun, Grock and Weinstock in Herbert (2016) EM:Rap 16(11): 11-12
Kostura (2019) Crit Dec Emerg Med 33(8):19-27
Orman and Mattu in Herbert (2015) EM:Rap 15(8):2-3
(2015) Ann Emerg Med 651(1): 32-42 [PubMed]
1. http://www.acep.org/workarea/DownloadAsset.aspx?id=100814
Bushnell (2005) Ann Emerg Med 46:90-92 [PubMed]
Gupta (2009) Pharmaceuticals 2: 66-76 [PubMed]
Hagan (2000) JAMA 283: 897-203 [PubMed]