**Core Concept**
Unstable angina pectoris is a clinical syndrome characterized by chest pain or discomfort at rest, often radiating to the jaw, arms, or back, associated with transient myocardial ischemia, but without evidence of myocardial necrosis. The clinical presentation, electrocardiographic changes, and negative cardiac enzymes in this patient are consistent with unstable angina.

**Why the Correct Answer is Right**
Coronary angiography is the most appropriate next step in management because it allows for the direct visualization of the coronary arteries, enabling the identification of significant coronary artery disease (CAD) and the assessment of the suitability for revascularization procedures, such as percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). The patient's ongoing chest pain symptoms, despite optimal medical therapy, suggest a high likelihood of significant CAD, and coronary angiography is essential to guide further management.

**Why Each Wrong Option is Incorrect**

**Option A:** IV streptokinase is a thrombolytic agent used in the treatment of acute myocardial infarction (MI), but it is not indicated in the management of unstable angina. Unstable angina is characterized by transient myocardial ischemia without evidence of MI, and thrombolytic therapy is not necessary in this scenario.

**Option C:** Exercise testing is not the most appropriate next step in management because it may exacerbate the patient's symptoms and is not necessary in the acute management of unstable angina. The patient's symptoms have not resolved with optimal medical therapy, and further testing is not required before proceeding with coronary angiography.

**Option D:** Oral aspirin is already part of the patient's treatment regimen, and increasing the dose or switching to IV aspirin is not necessary. The patient's symptoms have not responded to optimal medical therapy, and further management is required.

**Clinical Pearl / High-Yield Fact**
In patients with unstable angina, the presence of new ST-segment depression on ECG, as seen in this patient, is a marker of significant CAD and a predictor of adverse outcomes. Coronary angiography is essential in these patients to guide further management and improve outcomes.

**✓ Correct Answer: B. coronary angiography**