A 58-year-old man comes to the emergency department for complaints of crushing chest pain for 4 hours. He was shoveling snow outside when the pain started. It is rated 7/10 and radiates to his left arm. An electrocardiogram (ECG) demonstrates ST-segment elevation in leads V2-4. He subsequently undergoes percutaneous coronary intervention (PCI) and is discharged with aspirin, clopidogrel, carvedilol, atorvastatin, and lisinopril. Five days later, the patient is brought to the emergency department by his wife with complaints of dizziness. He reports lightheadedness and palpitations for the past 2 hours but otherwise feels fine. His temperature is 99.7°F (37.6°C), blood pressure is 95/55 mmHg, pulse is 105/min, and respirations are 17/min. A pulmonary artery catheter is performed and demonstrates an increase in oxygen concentration at the pulmonary artery. What finding would you expect in this patient?

Harsh, loud, holosystolic murmur at the lower left sternal border

Widespread ST-segment elevations

Drop of systolic blood pressure by 20 mmHg during inspiration

A 66-year-old female with hypertension and a recent history of acute ST-elevation myocardial infarction (STEMI) 6 days previous, treated with percutaneous transluminal angioplasty (PTA), presents with sudden onset chest pain, shortness of breath, diaphoresis, and syncope. Vitals are temperature 37°C (98.6°F), blood pressure 80/50 mm Hg, pulse 125/min, respirations 12/min, and oxygen saturation 92% on room air. On physical examination, the patient is pale and unresponsive. Cardiac exam reveals tachycardia and a pronounced holosystolic murmur loudest at the apex and radiates to the back. Lungs are clear to auscultation. Chest X-ray shows cardiomegaly with clear lung fields. ECG is significant for ST elevations in the precordial leads (V2-V4) and low-voltage QRS complexes. Emergency transthoracic echocardiography shows a left ventricular wall motion abnormality along with a significant pericardial effusion. The patient is intubated, and aggressive fluid resuscitation is initiated. What is the next best step in management?

Immediate transfer to the operating room

Immediate cardiac catheterization

Intra-aortic balloon counterpulsation

Administer dobutamine 5-10 mcg/kg/min IV

A 50-year-old man presents the emergency department for intense chest pain, profuse sweating, and shortness of breath. The onset of these symptoms was 3 hours ago. The chest pain began after a heated discussion with a colleague at the community college where he is employed. Upon arrival, he is found conscious and responsive; the vital signs include a blood pressure of 130/80 mm Hg, a heart rate at 90/min, a respiratory rate at 20/min, and a body temperature of 36.4°C (97.5°F). His medical history is significant for hypertension diagnosed 7 years ago, which is well-controlled with a calcium channel blocker. The initial electrocardiogram (ECG) shows ST-segment depression in multiple consecutive leads, an elevated cardiac troponin T level, and normal kidney function. Which of the following would you expect to find in this patient?

Incomplete occlusion of a coronary artery

Two days after undergoing an uncomplicated total thyroidectomy, a 63-year-old woman has acute, progressive chest pain. The pain is sharp and burning. She feels nauseated and short of breath. The patient has a history of hypertension, type 1 diabetes mellitus, medullary thyroid cancer, multiple endocrine neoplasia type 2A, anxiety, coronary artery disease, and gastroesophageal reflux disease. She smoked half a pack of cigarettes daily for 24 years but quit 18 years ago. Current medications include lisinopril, insulin glargine, insulin aspart, sertraline, aspirin, ranitidine, and levothyroxine. She appears anxious and diaphoretic. Her temperature is 37.4°C (99.3°F), pulse is 64/min, respirations are 17/min, and blood pressure is 148/77 mm Hg. The lungs are clear to auscultation. Examination shows a 3-cm linear incision over the anterior neck with 1 mm of surrounding erythema and mild serous discharge. The chest wall and abdomen are nontender. There is 5/5 strength in all extremities and decreased sensation to soft touch on the feet bilaterally. The remainder of the examination shows no abnormalities. Which of the following is the most appropriate next step in management?

Obtain an ECG and troponin T levels

Administer IV pantoprazole and schedule endoscopy

Discontinue levothyroxine and obtain fT4 levels

Administer IV levofloxacin and obtain chest radiograph

Obtain urine and plasma metanephrine levels

A 23-year-old man comes to the emergency department because of palpitations, dizziness, and substernal chest pain for three hours. The day prior, he was at a friend’s wedding, where he consumed seven glasses of wine. The patient appears diaphoretic. His pulse is 220/min and blood pressure is 120/84 mm Hg. Based on the patient's findings on electrocardiography, the physician diagnoses atrial fibrillation with rapid ventricular response and administers verapamil for rate control. Ten minutes later, the patient is unresponsive and loses consciousness. Despite resuscitative efforts, the patient dies. Histopathologic examination of the heart at autopsy shows an accessory atrioventricular conduction pathway. Electrocardiography prior to the onset of this patient's symptoms would most likely have shown which of the following findings?

Slurred upstroke of the QRS complex

Epsilon wave following the QRS complex

Prolongation of the QT interval

Cyclic alteration of the QRS axis

A 40-year-old woman comes to the physician for a 6-month history of recurrent episodes of chest pain, racing pulse, dizziness, and difficulty breathing. The episodes last up to several minutes. She also reports urinary urgency and two episodes of loss of consciousness followed by spontaneous recovery. There is no personal or family history of serious illness. She does not smoke or drink alcohol. Vitals signs are within normal limits. Cardiopulmonary examination shows no abnormalities. Holter monitoring is performed. ECG recordings during episodes of tachycardia show a QRS duration of 100 ms, regular RR-interval, and absent P waves. Which of the following is the most likely underlying cause of this patient's condition?

AV node with slow and fast pathway

Pre-excitation of the ventricles

Mutations in genes that code for myocyte ion channels

Macroreentrant rhythm in the right atria through cavotricuspid isthmus

Fibrosis of the sinoatrial node and surrounding myocardium

A 56-year-old patient developed excruciating chest discomfort in the past 72 hours, relieved by GTN spray. Troponin I is normal, and the ECG shows features of left ventricular hypertrophy (LVH) with T wave flattening. The patient is already on statins, aspirin, and metoprolol 50 mg . What is the next best step in management?

LMWH (Low Molecular Weight Heparin)

Arrange urgent coronary angiography

ECG interpretation in ACS for USMLE Step 1: High-Yield Internal Medicine Lessons

ECG Lead Anatomy - Know Your Angles

Coronary Arteries & ECG Leads Diagram

Frontal Plane (Limb Leads):
- Inferior: II, III, aVF (RCA)
- Lateral: I, aVL (LCx)
Transverse Plane (Precordial Leads):
- Septal: V1, V2 (LAD)
- Anterior: V3, V4 (LAD)
- Lateral: V5, V6 (LCx/LAD diagonal)

⭐ Posterior Wall MI: Look for ST depression and tall R waves in V1-V3 (reciprocal changes). Confirm with posterior leads (V7-V9) showing ST elevation.

STEMI Criteria & Evolution - Reading the Tombstones

STEMI Criteria: New ST-elevation at the J-point in ≥2 contiguous leads.
- Leads V2-V3: ≥2.5 mm in men <40y, ≥2 mm in men ≥40y, or ≥1.5 mm in women.
- Other leads (or posterior leads V7-V9): ≥1 mm.
- New or presumed new LBBB (Sgarbossa criteria apply).

ECG: Tombstone ST-elevation in V2-V4, Anterior STEMI

ECG Evolution:

⭐ Reciprocal ST depression (e.g., in leads I, aVL for inferior STEMI) helps differentiate STEMI from pericarditis, which causes diffuse ST elevation without reciprocal changes.

NSTEMI & Unstable Angina - The Depressed Heart

ECG Findings: ST-segment depression (≥0.5 mm) or deep, symmetric T-wave inversions (≥1 mm) in ≥2 contiguous leads.
Pathophysiology: Represents subendocardial ischemia, where demand outstrips supply, without full-thickness infarction.
UA vs. NSTEMI: ECGs can be identical; the presence of elevated cardiac biomarkers (troponins) defines NSTEMI.

ECG: ST depression and T-wave inversion

⭐ De Winter's T-waves: Upsloping ST depression at the J-point with tall, peaked T-waves in precordial leads. A high-risk finding considered a STEMI equivalent.

STEMI Equivalents - The Sneaky Killers

De Winter's T-waves: Upsloping ST depression >1mm at J-point + tall, peaked T-waves in precordial leads. Signals acute LAD occlusion.
Wellens' Syndrome: Deeply inverted or biphasic T-waves in V2-V3 (pain-free); indicates critical LAD stenosis. ⚠️ Stress test contraindicated.
Posterior MI: ST depression >0.5mm in V1-V3 with tall R waves (R/S >1). Confirm with ST elevation in posterior leads (V7-V9).
Left Main (LMCA) Occlusion: Widespread ST depression with ST elevation in aVR ≥ V1.

⭐ Wellens' syndrome ECG findings are classic when the patient is pain-free. During an episode of chest pain, the T-waves may transiently normalize or show ST-elevation.

Infarct Localization - Artery Pinpointer

Coronary Arteries & ECG Leads Diagram

Wall Affected	Leads with STE	Artery Involved
Anterior	V3-V4	Left Anterior Descending (LAD)
Septal	V1-V2	LAD
Lateral	I, aVL, V5-V6	Left Circumflex (LCX) / Diagonal
Inferior	II, III, aVF	Right Coronary Artery (RCA) / LCX

High‑Yield Points - ⚡ Biggest Takeaways

STEMI requires new ST-segment elevation at the J-point in ≥2 contiguous leads: ≥1 mm in most leads, with higher thresholds for leads V2-V3.

NSTEMI/Unstable Angina often presents with ST-segment depression (≥0.5 mm) or dynamic T-wave inversions (≥1 mm).

Reciprocal ST depression in anatomically opposite leads is a specific marker for acute STEMI.

Pathological Q waves typically indicate a prior or completed MI, not an acute ischemic event.

Suspect posterior MI with ST depression in V1-V3; confirm with posterior leads (V7-V9).

Wellens' syndrome (biphasic/deeply inverted T-waves in V2-V3) signals critical LAD stenosis.

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