A 60-year-old man has had angina on exertion for the past 6 years. A coronary angiogram performed 2 years ago showed 75% stenosis of the left circumflex coronary artery and 50% stenosis of the right coronary artery. For the past 3 weeks, the frequency and severity of his anginal attacks have increased, and pain sometimes occurs even when he is lying in bed. On physical examination, his blood pressure is 110/80 mm Hg, and pulse is 85/min with irregular beats. An ECG shows ST-segment elevation. Laboratory studies show serum glucose, 188 mg/dL; creatinine, 1.2 mg/dL; and troponin I, 1.5 ng/mL. Which of the following is most likely to explain these findings?

**Core Concept**
The patient's presentation suggests an acute coronary syndrome, likely caused by a sudden reduction in coronary blood flow. **Angina pectoris** is a symptom of transient myocardial ischemia, while **myocardial infarction** occurs when the ischemia is prolonged and causes tissue necrosis.

**Why the Correct Answer is Right**
Given the increase in frequency and severity of anginal attacks, along with **ST-segment elevation** on the ECG and elevated **troponin I**, the most likely diagnosis is an acute **myocardial infarction**, specifically a non-ST elevation myocardial infarction (NSTEMI) or ST-elevation myocardial infarction (STEMI) if the ST elevation is significant. The irregular beats could indicate **atrial fibrillation**, a common comorbidity in patients with coronary artery disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Would not directly explain the acute worsening of symptoms or the ECG and laboratory findings.
**Option B:** Might be a factor in the patient's overall condition but does not directly explain the acute coronary syndrome.
**Option C:** Could be relevant but is not the most direct explanation for the patient's current presentation.
**Option D:** Is not provided, but any option not explaining an acute coronary event would be incorrect.

**Clinical Pearl / High-Yield Fact**
In patients with chronic **angina pectoris**, a sudden increase in frequency or severity of symptoms, or symptoms occurring at rest, suggests an acute coronary syndrome, which requires immediate medical attention.

**Correct Answer:** D. Acute coronary syndrome, likely myocardial infarction.

✓ Correct Answer: A. Atheromatous plaque fissure with thrombosis