Aortic Dissection vs Pericarditis vs PE: Reasoning Through Acute Chest Pain
Clinical Reasoning · 9 min read · 2026-08-15
Introduction
Acute chest pain questions on Step 2 CK are rarely about whether the patient is sick - the vignette tells you that. They're about whether you can rank three dangerous diagnoses from a handful of words. Dissection, pericarditis, and PE each have a signature, and the exam hands you the signature if you know where to look.
Start With the Quality of the Pain
- Aortic dissection - "tearing" or "ripping," maximal at onset, often radiating to the interscapular back. Syncope or stroke-like deficits in the vignette should move dissection to the top immediately.
- Pericarditis - sharp, pleuritic, worse supine, relieved by sitting forward. Often preceded by a viral prodrome or recent MI (Dressler syndrome).
- Pulmonary embolism - pleuritic, sudden, with dyspnea out of proportion and tachycardia. Look for the risk-factor sentence: recent surgery, immobilization, long flight, estrogen therapy, prior VTE, malignancy.
The pain description is usually decided in the first two lines of the vignette. Read them twice.
The Exam Findings That Decide It
Beck's triad (hypotension, JVD, muffled sounds) is tamponade - a pericarditis complication the boards test as its own question. Note the asymmetry: a rub argues *for* pericarditis; absent breath sounds argue *against* it and toward pneumothorax.
ECG Patterns
- Pericarditis - diffuse concave ST elevation with PR depression, no reciprocal changes, not confined to one vascular territory. Diffuse is the word that matters.
- PE - sinus tachycardia is the most common finding. The famous S1Q3T3 pattern is specific but uncommon. Right heart strain (T-wave inversions V1-V4, right bundle branch block) appears in large emboli.
- Dissection - the ECG can be normal, or show inferior STEMI if the dissection flap occludes the right coronary artery. That combination - "STEMI plus tearing back pain" - is the trap: thrombolytics here are lethal.
The Confirmatory Test - and the One You Must Not Order
- Dissection - CT angiography of the chest in the stable patient; TEE if unstable. D-dimer is *not* the rule-out test here.
- Pericarditis - echo to assess for effusion; diagnosis is clinical plus ECG.
- PE - CT pulmonary angiography; D-dimer only when pretest probability is low (Wells score). In pregnancy or renal failure, V/Q scan.
The highest-yield reasoning move in this entire differential: a low-pretest-probability patient with pleuritic pain gets a D-dimer first, and a negative result ends the workup. Ordering CT-PA on everyone is the wrong answer choice, and the boards test it.
A Reasoning Sequence for the Vignette
- Tearing to the back + pulse/BP differential → dissection → CT-A chest.
- Sharp pain better leaning forward + diffuse ST elevation + rub → pericarditis → echo, NSAIDs + colchicine.
- Pleuritic pain + dyspnea + tachycardia + VTE risk factor → PE → Wells score, then D-dimer (low probability) or CT-PA (high probability).
- Chest pain + hypotension + JVD + muffled sounds → tamponade → emergent pericardiocentesis, no time for the CT scanner.
Common Pitfalls
- Anchoring on ACS for every chest pain vignette - if the ECG is diffuse rather than territorial, stop and reconsider.
- Using D-dimer to "rule out" dissection; it doesn't.
- Missing the viral prodrome sentence that quietly points to pericarditis.
- Forgetting that a young woman on oral contraceptives with calf swelling is a PE vignette even when the chest pain is mild.
Conclusion
Chest pain triage on the boards is a pattern-matching exercise only after you've disciplined the order of operations: pain character, then exam signs, then ECG territory, then the right confirmatory test. Build that chain with timed practice and the three-diagnosis chest pain question becomes free points.