What is the best approach to diagnose an aortic dissection?

How to Diagnose Aortic Dissection

The optimal diagnostic approach depends on hemodynamic stability: use CT angiography (CTA) as first-line imaging in stable patients, and transesophageal echocardiography (TEE) in unstable patients who cannot be safely transported. 1, 2

Initial Clinical Assessment

When aortic dissection is suspected, immediately evaluate for:

• Tearing or ripping chest pain radiating to the back 3
• Blood pressure differential >20 mmHg between arms 3
• Pulse deficits or neurological deficits 3
• New aortic regurgitation murmur 3
• Troponin elevation (occurs in 23-27% of cases due to coronary ostial involvement or hemodynamic stress, not false positive) 3

Diagnostic Algorithm Based on Hemodynamic Status

For Hemodynamically Stable Patients

CT angiography is the preferred first-line test with sensitivity of 93-98% and specificity of 87-100%. 2, 4

• CTA provides rapid diagnosis and has the added benefit of detecting alternative diagnoses in 13% of cases 2
• Accuracy is similar to TEE and MRA 2
• Readily available in most emergency departments 1

For Hemodynamically Unstable Patients

Perform bedside transthoracic echocardiography (TTE) immediately, followed by TEE if needed. 1, 2

• TTE can be performed at bedside but has limited sensitivity (77-80%) and often inadequate image quality in critically ill patients 1, 2
• If cardiac tamponade is identified on TTE, proceed directly to surgery without further imaging 1
• TEE should be the definitive diagnostic test in unstable patients with sensitivity of 99% and specificity of 89% when performed by experienced operators 1, 2
• TEE can be performed in the ICU or operating room as the sole diagnostic procedure before emergency surgery 2

Imaging Modality Comparison

CT Angiography

• Sensitivity: 93-98%, Specificity: 87-100% 2, 4
• Widely available and rapid 1
• Excellent for detecting thrombus, pericardial effusion, and branch vessel involvement 1
• Less effective at detecting entry/reentry tears compared to TEE and MRI 1

Transesophageal Echocardiography (TEE)

• Sensitivity: 99%, Specificity: 89% (in experienced hands) 1, 2
• Can be performed at bedside in unstable patients 2, 5
• Excellent for detecting entry tears and aortic regurgitation 4
• Critical limitation: "blind spot" in distal ascending aorta and anterior aortic arch due to tracheal interposition 1, 2
• Operator-dependent and requires experienced examiners 2

Magnetic Resonance Angiography (MRA)

• Highest sensitivity: 100%, Specificity: 100% 6, 2, 4
• Best for comprehensive evaluation including extent, entry/reentry tears, branch vessel involvement, and aortic regurgitation 6, 4
• Major limitation: not available on emergency basis in most centers 6
• Examination time of 20-30 minutes makes it impractical for unstable patients 6
• Consider for stable patients when detailed anatomical information is needed for surgical planning 6, 4

Aortography

• Sensitivity: 77-88%, Specificity: >95% 1
• No longer recommended as first-line diagnostic test due to lower sensitivity than newer modalities 1, 7
• May miss completely thrombosed false lumen or intramural hematoma 1
• Reserved for specific situations: evaluating coronary anatomy before surgery or assessing branch vessel compromise in patients with organ ischemia 1, 5

Critical Pitfalls to Avoid

Never assume acute coronary syndrome based solely on troponin elevation and chest pain—always consider aortic dissection before administering anticoagulation or fibrinolytics, which would be catastrophic. 3

• Do not use multiple imaging modalities sequentially as this causes unnecessary time loss; one definitive test is sufficient 1
• Avoid pericardiocentesis in suspected dissection with tamponade, as reducing intrapericardial pressure may cause recurrent bleeding 1
• TTE alone is insufficient for comprehensive evaluation due to poor sensitivity (77-80%) 1, 2
• Be aware of TEE artifacts from reverberation in the ascending aorta that can lead to false diagnoses 2

Special Considerations

When IV Contrast is Contraindicated

Use non-contrast MRA with ECG-gated balanced steady-state free precession (bSSFP) sequences, which achieves near 100% accuracy for detecting thoracic aortic dissection. 6

Coronary Artery Evaluation

Coronary angiography remains the gold standard for evaluating coronary involvement when chronic coronary disease is suspected (present in 25% of patients), though newer MRI techniques are emerging. 1, 6

Intramural Hematoma

MRI can detect intramural hemorrhages showing thickened aortic wall (>7 mm) with high signal intensity from methemoglobin formation. 1, 6

Institutional Protocol Recommendation

Each institution should establish a single, rapid diagnostic pathway based on local availability and expertise. 1

• Stable patients: CTA as first-line
• Unstable patients: Bedside TTE → TEE if needed
• Transfer to surgical center if dissection suspected and local capabilities inadequate 1