Chest pain look-alikes: dissection, STEMI, pericarditis, PE and tension pneumothorax

"A 58-year-old man comes to the emergency department with sudden chest pain." Many very different diagnoses can follow that sentence, and their treatments conflict. The heparin that saves a patient with a pulmonary embolism can kill a patient with an aortic dissection. Exam writers know this, so the stem usually hides one detail that decides the answer. Here is where to look.

The five at a glance

Diagnosis	The pain	The clue that decides it	Next step in diagnosis	Next step in management
Aortic dissection	Sudden, severe, tearing or ripping; goes through to the back and can run down into the abdomen	Hypertension (the most common cause), cocaine, pregnancy, or in a young patient Marfan, Ehlers-Danlos, Turner syndrome or coarctation. A blood pressure difference between the arms, a new diastolic murmur, a widened mediastinum	Check the blood pressure in both arms. CT angiography if stable; transesophageal echo if unstable or allergic to contrast	IV beta-blocker first, then a vasodilator if needed; surgery for type A. No thrombolytics or anticoagulants
STEMI	Pressure or squeezing that builds; spreads to the arm or jaw; sweating, nausea	ST elevation in leads that match one coronary territory, with reciprocal ST depression	ECG within 10 minutes of arrival; troponin, repeated if the first is negative	Aspirin, then primary PCI
Acute pericarditis	Sharp and pleuritic; may spread to the trapezius ridge; better sitting up and leaning forward, worse lying flat	Friction rub, heard best with the patient leaning forward	ECG: PR depression and ST elevation in every lead except aVR and V1, which show ST depression	Depends on the cause (see below)
Pulmonary embolism	Sudden pleuritic pain with shortness of breath	Tachycardia and low oxygen with clear lungs; a swollen leg; recent surgery; a new right bundle branch block	CT pulmonary angiography; a V/Q scan if the eGFR is under 30	Anticoagulation (a DOAC unless the eGFR is under 30); thrombolysis if hypotensive
Tension pneumothorax	Sudden pain and shortness of breath, often after trauma, a central line or ventilation	Low blood pressure, distended neck veins, absent breath sounds on one side, trachea shifted away	None: it's a clinical diagnosis, so don't wait for an x-ray	Immediate needle decompression, then a chest tube

Aortic dissection, step by step

1. Suspect it from tearing pain that radiates to the back, and check the blood pressure in both arms. A chest x-ray may show a widened mediastinum.
2. Lower the heart rate first with an IV beta-blocker such as labetalol or esmolol, to about 60 a minute, and the systolic pressure to under 120. Add a vasodilator such as nitroprusside only after that; on its own it causes reflex tachycardia, which increases the shear on the tear.
3. Confirm it. CT angiography if the patient is stable. Transesophageal echo if the patient is too unstable to leave the emergency department, which is often done in the operating room, or if the patient has had anaphylaxis to contrast.
4. Treat by type. Type A (ascending aorta) goes to emergency surgery. Complicated type B gets endovascular repair. Uncomplicated type B is managed medically with follow-up imaging.

As the false lumen spreads, it blocks the branches of the aorta, and each complication changes the stem: an inferior STEMI (right coronary ostium), tamponade, acute aortic regurgitation, a weak pulse in one arm (subclavian), a stroke (carotid), paraplegia (intercostal arteries), bowel ischemia, hematuria and flank pain (renal), or a cold leg (iliac).

The pairs that get confused

Dissection or STEMI?

Both cause sudden, severe chest pain in an older patient with hypertension. Dissection pain is worst at the very start and tears through to the back. MI pain builds over minutes.

What separates these cases: the pain going through to the back, a new diastolic murmur, and a blood pressure difference between the arms point to dissection, even when the ECG shows ST elevation. A dissection flap can block the right coronary ostium and cause an inferior STEMI (II, III and aVF), and a thrombolytic given to that patient can be fatal. Equal arm pressures don't rule it out.

Pericarditis or STEMI?

What separates these cases: pericarditis raises the ST segment in almost every lead and depresses the PR segment, with ST depression only in aVR and V1. Its pain changes with position and breathing. A STEMI follows one coronary territory and shows reciprocal depression.

Once you've called it pericarditis, the next question is usually the cause, because the treatment follows it:

Setting	Next step in management
Recent viral illness, or no cause found	Aspirin or an NSAID, plus colchicine
High creatinine and BUN (uremic pericarditis)	Dialysis
First week after a large MI (peri-infarction pericarditis)	Aspirin plus colchicine; avoid other NSAIDs and steroids
Weeks after an MI or cardiac surgery (post-cardiac injury syndrome)	Aspirin or an NSAID, plus colchicine
Fever and an effusion (purulent pericarditis)	Pericardiocentesis and IV antibiotics

Pulmonary embolism or tension pneumothorax?

What separates these cases: listen to the chest. With a pulmonary embolism the lungs usually sound normal. A tension pneumothorax has absent breath sounds on one side, with low blood pressure and distended neck veins.

Three more look-alikes the exam likes

Diagnosis	The clue	The trap
Cocaine-induced vasospasm	A young patient with chest pain, sweating, dilated pupils and agitation; nasal bleeding or a perforated septum; troponin elevated. Patients often deny drug use	No beta-blocker: it leaves alpha-1 vasoconstriction unopposed. Remember "DAN does cocaine": diazepam, aspirin, nitrates
Variant (Prinzmetal) angina	A young patient without risk factors, chest pain at night, transient ST elevation	Treat with a calcium channel blocker or nitrates; avoid aspirin and beta-blockers, which can worsen vasospasm
Takotsubo cardiomyopathy	Chest pain after severe emotional or physical stress; ST elevation; apical ballooning on echo; normal coronary arteries	If the ejection fraction is under 40%, start a beta-blocker and an ACE inhibitor and repeat the echo in a few weeks

A bonus trap: low blood pressure and distended neck veins

Four patients arrive hypotensive with distended neck veins and clear lungs. Each needs a different treatment, and the wrong one makes things worse.

Diagnosis	The clue	Next step in management
Tension pneumothorax	Absent breath sounds on one side	Needle decompression
Cardiac tamponade	Muffled heart sounds, pulsus paradoxus, equal diastolic pressures in every chamber. Days after an MI, think free wall rupture	Echo first if stable, then pericardiocentesis; never furosemide, which lowers preload and worsens it
Right ventricular infarction	ST elevation in II, III and aVF, and in V4R; high right-sided pressures with a low wedge pressure	IV fluids, with dobutamine if needed; avoid nitrates and diuretics
Massive pulmonary embolism	After surgery or immobility; sinus tachycardia and a new right bundle branch block	Thrombolysis

What separates these cases: the breath sounds point to the pneumothorax, the heart sounds point to tamponade, and the ECG points to the right ventricle or to the right-heart strain of a pulmonary embolism.

Try these cases from the Pradis question bank

Each case below is adapted from a row in the Pradis Cardiology chapter. Decide before you read the answer.

1. A 35-year-old man has chest pain, sweating, dilated pupils and agitation. He denies drug use. The exam shows nasal bleeding and a small perforation of the nasal septum. Troponin is elevated.
Answer: cocaine-induced vasospasm. Patients deny drug use; it's the exam's favorite red herring. Give diazepam, aspirin and nitrates, and no beta-blocker.

2. A 60-year-old woman develops chest pain at her daughter's funeral. The ECG shows ST elevation, the echo shows apical ballooning, and angiography shows normal coronary arteries.
Answer: stress-induced (Takotsubo) cardiomyopathy. A surge of stress hormones stuns the heart; the hypokinesis usually resolves with time.

3. A 17-year-old girl with short stature, a webbed neck and no periods has sudden, severe chest pain radiating to her back. There is a systolic ejection murmur.
Answer: aortic dissection. Turner syndrome brings a bicuspid aortic valve and coarctation, both of which predispose to it.

4. Two weeks after a STEMI, a 55-year-old man has sudden pleuritic chest pain, a heart rate of 110, mild swelling of the right leg, a scratchy sound at the right lung base and a new right bundle branch block.
Answer: pulmonary embolism. Any cause of pleuritic pain can produce a friction rub. The asymmetric leg swelling points to the source, and the new right bundle branch block to right-heart strain.

5. Two weeks after coronary bypass surgery, a 65-year-old man has sharp pleuritic chest pain, a fever of 38 °C and a white count of 11,000.
Answer: post-cardiac injury syndrome. The pain doesn't change with leaning forward, which points away from simple pericarditis.

6. Three days after an anterior MI, a man suddenly becomes hypotensive with distended neck veins, muffled heart sounds and clear lungs. His chest x-ray shows a normal heart size.
Answer: free wall rupture with tamponade. In acute tamponade the pericardium hasn't had time to stretch, so the classic large, globular heart is missing.

7. A 65-year-old man has sharp chest pain radiating to his back and passed out before calling 911. His blood pressure is 170/80 in both arms, the chest x-ray shows a widened mediastinum, and troponin is mildly elevated. While the cardiothoracic surgeon is being called, what do you start first?
Answer: IV labetalol, to bring the heart rate under 60 before any vasodilator, then CT angiography to confirm. His equal arm pressures didn't rule out a dissection.

How to study these

Learn each pair by the clue that separates it, not by the full description of each disease. On the exam you'll rarely need everything about pericarditis; you'll need the one line that rules out STEMI.

That's how Pradis is built. Each row of a look-alike table is its own question with its own stars, so the pair you keep mixing up comes back on its own schedule until you stop mixing it up. The Biostatistics chapter is free once you log in.

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Written for USMLE Step 2 CK and shelf exam preparation. In patient care, follow current guidelines and your institution's protocols.