A 42-year-old woman reports fatigue, shortness of breath, back pain, and nausea. The ECG shows ST-segment depression and nonsustained ventricular tachycardia. What is the most likely diagnosis?

The presentation of the patient, including fatigue, shortness of breath, back pain, and nausea, alongside the ECG findings of ST-segment depression and nonsustained ventricular tachycardia, points towards a diagnosis that indicates a significant risk for acute coronary syndrome (ACS). High-risk non-ST-segment elevation ACS is characterized by symptoms of ischemia or evidence of cardiac involvement without full-blown myocardial infarction (e.g., ST elevation).

The ST-segment depression observed on the ECG suggests myocardial ischemia, indicating that the heart muscle is not getting enough blood flow, which aligns with the patient's clinical complaints. The nonsustained ventricular tachycardia signifies potential electrical instability related to ischemic heart tissue. The combination of these findings suggests that the patient is experiencing a high-risk clinical scenario related to ACS, possibly indicating that the cardiac function is compromised.

Additionally, other options such as unstable or stable angina might be considered; however, the presence of nonsustained ventricular tachycardia and the particular symptom profile points toward a more severe condition than typical angina. Unstable angina may present with similar symptoms but does not typically exhibit nonsustained ventricular tachycardia nor would it usually result in significant ST-segment changes on