A 28-year-old male presents with sharp, stabbing chest pain that worsens when lying flat and improves when sitting forward. He reports a recent viral upper respiratory infection 2 weeks ago. On examination, a friction rub is heard on auscultation. His vital signs are stable. An ECG is most likely to show which of the following findings in this patient?

Diffuse, concave ST-segment elevations

Peaked T waves and ST-segment elevations in leads V1-V6

S waves in lead I, Q waves in lead III, and inverted T waves in lead III

Alternating high and low amplitude QRS complexes

A 74-year-old man presents with complaints of sudden severe crushing retrosternal pain. The pain radiated to his left arm shortly after it began, and he was subsequently rushed to the emergency department for evaluation. His troponins and creatine kinase-MB (CK-MB) were elevated. Unfortunately, the patient died within the next 2 hours and an autopsy was performed immediately. The gross examination of the heart will show?

White, patchy, non-contractile scar

Red granulation tissue surrounding the infarction

A 56-year-old male died in a motor vehicle accident. Autopsy reveals extensive atherosclerosis of his left anterior descending artery marked by intimal smooth muscle and collagen proliferation. Which of the following is implicated in recruiting smooth muscle cells from the media to intima in atherosclerotic lesions?

Vascular endothelial growth factor

A 72-year-old man comes to the physician because of a 2-month history of intermittent retrosternal chest pain and tightness on exertion. He has type 2 diabetes mellitus, osteoarthritis of the right hip, and hypertension. Current medications include insulin, ibuprofen, enalapril, and hydrochlorothiazide. Vital signs are within normal limits. His troponin level is within the reference range. An ECG at rest shows a right bundle branch block and infrequent premature ventricular contractions. The patient's symptoms are reproduced during adenosine stress testing. Repeat ECG during stress testing shows new ST depression of > 1 mm in leads V2, V3, and V4. Which of the following is the most important underlying mechanism of this patient's ECG changes?

Diversion of blood flow from stenotic coronary arteries

Transient atrioventricular nodal blockade

Reduced left ventricular preload

Ruptured cholesterol plaque within a coronary vessel

Increased myocardial oxygen demand

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

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 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

ACS pathophysiology and classification for USMLE Step 1: High-Yield Internal Medicine Lessons

Pathophysiology - Plaque Attack

Vulnerable Plaque Rupture & Thrombus Formation

Atherosclerosis builds vulnerable plaques: large lipid cores, thin fibrous caps, and active inflammation.
Rupture is triggered by:
- Inflammation: Macrophages release matrix metalloproteinases (MMPs) that digest the fibrous cap.
- Shear Stress: Mechanical force from blood flow.

⭐ Macrophages are key culprits; they secrete matrix metalloproteinases (MMPs) that degrade the plaque's protective fibrous cap, making it prone to rupture.

📌 Mnemonic (Pathway): Rupture → Exposure → Adhesion → Coagulation → Thrombus (REACT).

Myocardial Ischemia - The Energy Crisis

Pathogenesis: Imbalance between myocardial oxygen supply and demand, most often from coronary artery obstruction.
Cellular Cascade:
- Switch from aerobic to anaerobic metabolism → $↓ATP$ & $↑Lactate$.
- Failure of ion pumps (e.g., $Na^+/K^+$ ATPase) → ion imbalance & cellular swelling.
Injury Spectrum:
- Reversible: < 20 min of ischemia leads to stunned or hibernating myocardium.
- Irreversible: Ischemia lasting ~20-40 minutes or more results in coagulative necrosis.

⭐ Vulnerability Hotspot: The subendocardium is the most vulnerable region to ischemia due to its high oxygen demand and tenuous blood supply.

ACS Classification - The Great Divide

ECG is the critical first step. It divides Acute Coronary Syndrome (ACS) into two main pathways: ST-Elevation Myocardial Infarction (STEMI) and Non-ST-Elevation ACS (NSTE-ACS), guiding immediate reperfusion strategy.

STEMI: Caused by a fully occlusive thrombus leading to transmural ischemia. ECG shows persistent ST-segment elevation in ≥2 contiguous leads.
NSTE-ACS (UA/NSTEMI): From a partially occlusive thrombus causing subendocardial ischemia. ECG may show ST-depression or T-wave inversions.
- Cardiac biomarkers are the tie-breaker:
  - NSTEMI: Positive troponins (myocardial necrosis).
  - Unstable Angina (UA): Negative troponins (ischemia without necrosis).

⭐ A posterior wall STEMI may not show classic ST elevation; instead, look for ST depression in leads V1-V3 and consider posterior leads (V7-V9).

Cardiac Biomarkers - The Troponin Tale

Troponin I & T: Most sensitive and specific markers for myocardial necrosis.
- Rises in 2-4 hrs, peaks at ~24-48 hrs, and remains elevated for 7-14 days.
CK-MB: Useful for detecting re-infarction due to its shorter duration.
- Rises in 4-6 hrs, peaks at ~24 hrs, and normalizes within 48-72 hrs.
Myoglobin: Earliest marker to rise, but lacks specificity.

Cardiac Troponin Levels and Assay Generations

⭐ High-sensitivity troponin (hs-cTn) can detect myocardial injury earlier, but a negative result within the first few hours of symptom onset does not rule out ACS.

ACS is a spectrum from unstable angina (UA) to MI, driven by plaque rupture and intracoronary thrombosis.

UA vs. NSTEMI is distinguished by cardiac biomarkers; troponins are elevated only in NSTEMI.

NSTEMI vs. STEMI is distinguished by ECG: NSTEMI has ST depression/T-wave inversion, while STEMI has ST-segment elevation.

Complete coronary occlusion causes a STEMI, whereas partial occlusion leads to UA or NSTEMI.

The fundamental problem is a mismatch in myocardial oxygen supply and demand.

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