A 71-year-old man develops worsening chest pressure while shoveling snow in the morning. He tells his wife that he has a squeezing pain that is radiating to his jaw and left arm. His wife calls for an ambulance. On the way, he received chewable aspirin and 3 doses of sublingual nitroglycerin with little relief of pain. He has borderline diabetes and essential hypertension. He has smoked 15–20 cigarettes daily for the past 37 years. His blood pressure is 172/91 mm Hg, the heart rate is 111/min and the temperature is 36.7°C (98.0°F). On physical examination in the emergency department, he looks pale, very anxious and diaphoretic. His ECG is shown in the image. Troponin levels are elevated. Which of the following is the best next step in the management of this patient condition?

Clopidogrel, atenolol, anticoagulation and monitoring

CT scan of the chest with contrast

A cardiologist is studying how a new virus that infects the heart affects the electrical conduction system of the cardiac myocytes. He decides to obtain electrocardiograms on patients with this disease in order to see how the wave patterns and durations change over time. While studying these records, he asks a medical student who is working with him to interpret the traces. Specifically, he asks her to identify the part that represents initial ventricular depolarization. Which of the following characteristics is most consistent with this feature of the electrocardiogram?

Normal duration defined as less than 120 milliseconds

Elevated in patients with full thickness ischemic injury of the heart

Becomes peaked in states of hyperkalemia

Becomes prominent in states of hypokalemia

Normal duration defined as less than 200 milliseconds

A 69-year-old man is scheduled to undergo radical retropubic prostatectomy for prostate cancer in 2 weeks. He had a myocardial infarction at the age of 54 years. He has a history of GERD, unstable angina, hyperlipidemia, and severe osteoarthritis in the left hip. He is unable to climb up stairs or walk fast because of pain in his left hip. He had smoked one pack of cigarettes daily for 30 years but quit 25 years ago. He drinks one glass of wine daily. Current medications include aspirin, metoprolol, lisinopril, rosuvastatin, omeprazole, and ibuprofen as needed. His temperature is 36.4°C (97.5°F), pulse is 90/min, and blood pressure is 136/88 mm Hg. Physical examination shows no abnormalities. A 12-lead ECG shows Q waves and inverted T waves in leads II, III, and aVF. His B-type natriuretic protein is 84 pg/mL (N < 125). Which of the following is the most appropriate next step in management to assess this patient's perioperative cardiac risk?

Radionuclide myocardial perfusion imaging

24-hour ambulatory ECG monitoring

Seventy-two hours after admission for an acute myocardial infarction, a 48-year-old man develops dyspnea and a productive cough with frothy sputum. Physical examination shows coarse crackles in both lungs and a blowing, holosystolic murmur heard best at the apex. ECG shows Q waves in the anteroseptal leads. Pulmonary capillary wedge pressure is 23 mm Hg. Which of the following is the most likely cause of this patient’s current condition?

Rupture of the chordae tendineae

Rupture of the ventricular free wall

Postmyocardial infarction syndrome

Rupture of the interventricular septum

A 60-year-old African American gentleman presents to the emergency department with sudden onset "vice-like" chest pain, diaphoresis, and pain radiating to his left shoulder. He has ST elevations on his EKG and elevated cardiac enzymes. Concerning his current pathophysiology, which of the following changes would you expect to see in this patient?

Decreased cardiac output; increased systemic vascular resistance

No change in cardiac output; decreased venous return

Increased cardiac output; increased systemic vascular resistance

Increased cardiac output; decreased systemic vascular resistance

Decreased cardiac output; decreased venous return

A 25-year-old man comes to the emergency department because of a 1-week-history of progressively worsening dyspnea and intermittent chest pain that increases on inspiration. He had an upper respiratory tract infection 2 weeks ago. His pulse is 115/min and blood pressure is 100/65 mm Hg. Examination shows inspiratory crackles bilaterally. His serum troponin I is 0.21 ng/mL (N < 0.1). An x-ray of the chest shows an enlarged cardiac silhouette and prominent vascular markings in both lung fields; costophrenic angles are blunted. A rhythm strip shows inverted T waves. Which of the following additional findings is most likely in this patient's condition?

Elevated brain natriuretic peptide

Opening snap with low-pitched diastolic rumble

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

Cardiac biomarkers for USMLE Step 3: High-Yield Internal Medicine Lessons

Biomarkers 101 - Heart's SOS Signals

Troponins (cTnI, cTnT): Most sensitive & specific for myocardial necrosis. Rise in 2-4h, peak at 24-48h, stay elevated for 7-10 days.
CK-MB: Rises in 4-6h, peaks at 12-24h, normalizes in 48-72h. Useful for detecting re-infarction.

Cardiac Biomarker Kinetics Post-MI

⭐ High-sensitivity troponins (hs-cTn) have high negative predictive value, allowing for rapid rule-out of ACS.

Troponins - The Gold Standard

Most sensitive & specific markers for myocardial necrosis.
Two main cardiac-specific isoforms: Troponin I (cTnI) and Troponin T (cTnT).
Timeline of Release after MI:
- Rise: 2-4 hours
- Peak: 12-24 hours
- Return to Baseline:
  - cTnI: 7-10 days
  - cTnT: 10-14 days

Cardiac Troponin Levels After Myocardial Infarction

⭐ High-sensitivity troponins (hs-cTn) have a high negative predictive value (>99%), effectively ruling out MI if negative at presentation and after 1-2 hours.

💡 Falsely elevated troponins can occur in renal failure, sepsis, and myocarditis.

CK-MB & Myoglobin - Old Guard, Early Bird

Myoglobin:
- Earliest riser: ↑ within 1-4 hrs post-MI.
- Peaks at 6-7 hrs, normalizes in 24 hrs.
- Low specificity (skeletal muscle injury); a negative result can help rule out MI.
Creatine Kinase-MB (CK-MB):
- Rises in 3-6 hrs, peaks at 12-24 hrs, baseline in 48-72 hrs.
- Less specific than troponin (found in skeletal muscle).
- Main advantage: shorter duration allows for detection of re-infarction.

⭐ High-Yield: CK-MB's key modern role is detecting re-infarction. A second rise after returning to baseline suggests a new ischemic event, a detail troponins might obscure due to their prolonged elevation.

Clinical Algorithm - The ACS Playbook

Initial Actions: ECG within 10 min, IV access, chewable Aspirin (325 mg), Nitroglycerin, O₂ if SpO₂ <90%.
Core Meds (MONA-BASH):
- Dual Antiplatelet Therapy (Aspirin + P2Y12 inhibitor)
- Anticoagulation (Heparin)
- Beta-blocker (within 24h if no contraindications)
- High-intensity Statin
- Nitrates (for pain)
- Morphine (refractory pain)

⭐ In NSTE-ACS, the GRACE score is more accurate than the TIMI score for predicting in-hospital and 6-month mortality.

High‑Yield Points - ⚡ Biggest Takeaways

Troponins (I & T) are the most sensitive and specific markers for MI; they remain elevated for 7-14 days.

CK-MB is the best marker for detecting re-infarction due to its rapid normalization within 48-72 hours.

Myoglobin is the earliest biomarker to rise but is highly non-specific for cardiac injury.

High-sensitivity troponins (hs-cTn) have a high negative predictive value, allowing for a faster rule-out of MI.

MI diagnosis requires a dynamic rise and/or fall of biomarkers; a normal ECG does not exclude MI.

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