How can emergency department clinicians differentiate myocardial infarction from aortic dissection?

Differentiating MI from Aortic Dissection in the Emergency Department

In the ED, immediately perform a focused cardiovascular exam looking for pulse differentials between limbs and blood pressure differentials between arms (>20 mmHg), check for aortic regurgitation murmur (especially if eccentric on echo), and obtain CT angiography as the definitive diagnostic test—while recognizing that D-dimer >500 ng/mL combined with clinical risk scores can help stratify suspicion before imaging. 1, 2

Clinical Presentation: Key Distinguishing Features

The history and physical examination provide critical early clues, though overlap exists:

Aortic Dissection typically presents with:

• Sudden onset of severe "sharp" or "stabbing" pain (not the classic "tearing/ripping" most commonly) 2
• Pain maximal at onset, often in chest or back
• Less likely to have chest pain as primary complaint (47% vs 85% for ACS) 3
• Less likely to describe pain as "tight/heavy" (5% vs 37% for ACS) 3
• More likely to have focal lower extremity neurological deficits (6% vs 1%) 3
• Bradycardia more common (15% vs 5% for ACS) 3
• Tachypnea more common (53% vs 22% for ACS) 3

MI typically presents with:

• Chest pain more common (85% vs 47%) 3
• Associated with diabetes, head/neck pain, dizziness, palpitations, and history of prior MI 3
• Increasing heart rate is an independent predictor of ACS over dissection 3

Physical Examination: Critical Findings

Perform these specific maneuvers immediately 1, 2:

• Blood pressure in all four extremities: BP differential between arms or between upper and lower extremities suggests dissection, though sensitivity is only 30% 1
• Pulse examination: Limb pulse differentials suggest dissection 1
• Cardiac auscultation:
  • Eccentric aortic regurgitation murmur is a critical finding that should immediately raise suspicion for type A dissection 4, 5
  • New diastolic murmur of AR in a patient with suspected MI should halt any reperfusion therapy until dissection is ruled out 5
• Neurological exam: Focal deficits suggest dissection 3

Diagnostic Algorithm

Step 1: Immediate Bedside Assessment

Point-of-care transthoracic echocardiography should be performed when dissection is suspected 4, 6:

• Look specifically for eccentric aortic regurgitation—this finding in a patient with chest pain and ECG changes should immediately trigger dissection workup 4, 5
• Assess for ascending aortic dilation
• Serial daily echos can show rapid AR progression (mild to severe within 72 hours) 5

Step 2: Laboratory Testing

D-dimer is useful for risk stratification 2, 7, 4:

• D-dimer <500 ng/mL makes dissection unlikely in low-risk patients 2
• Setting cutoff at 0.8-0.9 μg/mL provides 93.1% sensitivity for aortic dissection 7
• Elevated D-dimer combined with eccentric AR on echo strongly suggests dissection 4

Step 3: Risk Scoring

Apply validated risk scores before imaging 2:

• Aortic Dissection Detection Risk Score (AAD-RS) or AORTAs score can stratify probability
• Integrating low risk score with low D-dimer can exclude dissection 2

Step 4: Definitive Imaging

CT angiography is the first-line diagnostic test 2:

• Wide availability, speed, accuracy, and anatomic detail
• Should be obtained emergently when dissection is suspected
• TEE and MRI are reasonable alternatives but less practical in acute setting 2

Plain chest X-ray findings that raise suspicion (though neither sensitive nor specific) 2:

• Widened mediastinum: M-ratio (maximum upper mediastinal diameter/maximum thoracic diameter) >0.309 has 93.1% sensitivity for dissection 7

Critical Pitfalls to Avoid

DO NOT perform coronary angiography or PCI if dissection is suspected 4, 8:

• Three patients in one series had eccentric AR detected on TTE before angiography, but dissection was missed—all underwent angiography with catastrophic results 4
• PCI in unrecognized dissection exacerbates dissection progression and surgical hemostatic difficulty, markedly increasing mortality 8
• Mortality rate for type A dissection presenting as MI is 36% 4

If coronary angiography is already underway 6, 9:

• Difficulty engaging coronary arteries should prompt immediate suspicion 4, 6
• Intravascular ultrasound can diagnose dissection during PCI and may allow PCI as bridge to surgery if coronary occlusion confirmed 9

Special consideration for ECMO patients 10:

• Retrograde ECMO flow creates false-positive dissection flaps on imaging
• Requires context-aware interpretation and potentially modified imaging protocols

When Both Conditions Coexist

Type A dissection can cause MI through coronary ostial involvement 4, 8, 5:

• 5% of type A dissections present with MI 4
• Presence of eccentric AR + elevated troponins + ST changes should trigger dissection workup before any reperfusion therapy 4, 5
• If dissection with coronary involvement confirmed, emergency PCI may serve as bridge to definitive aortic surgery 9

Summary Algorithm

1. Measure BP in all four extremities + check pulses
2. Perform bedside TTE looking for eccentric AR and aortic dilation
3. Check D-dimer if dissection suspected
4. If any red flags present (pulse/BP differential, eccentric AR, elevated D-dimer, atypical pain pattern): obtain emergent CT angiography before any reperfusion therapy
5. If CT unavailable, TEE is reasonable alternative 2

The key principle: When in doubt, image the aorta before treating as isolated MI—the consequences of missed dissection with inappropriate thrombolysis or PCI are catastrophic 8.