Situation: A 58-year-old man is brought to the emergency room (ER) at 10:00 with crushing substernal chest pain that began at 09:20 while he was resting at home. He has hypertension and smokes one pack of cigarettes a day. He has no known drug allergies and no history of bleeding, peptic ulcer, or stroke. His 12-lead electrocardiogram (ECG) shows ST-segment depression in leads V4 to V6 with no ST-segment elevation. His high-sensitivity cardiac troponin is below the upper reference limit at arrival and again 2 hours later, with no significant change between the two results. How should the nurse classify his condition?

Unstable angina, non-ST-elevation myocardial infarction, and ST-elevation myocardial infarction together form the acute coronary syndrome. Unstable angina is new, worsening, or rest pain with ischemic changes but no troponin elevation; a troponin rise would make it an infarction. Rest pain with ST depression and normal high-sensitivity troponin at 0 and 2 hours therefore classifies him as unstable angina.

Classification of Acute Coronary Syndrome

The patient’s presentation fits the acute coronary syndrome (ACS) spectrum, which includes unstable angina, non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI). The key discriminator in this case is the troponin result. In unstable angina, myocardial ischemia produces symptoms and ECG changes, but necrosis has not occurred, so cardiac troponin remains below the upper reference limit. A rise in troponin would shift the diagnosis to NSTEMI .

Rest pain with ischemic ST-segment depression and normal high-sensitivity troponin at 0 and 2 hours classifies the patient as unstable angina. The crushing substernal chest pain began at rest, which is a high-risk feature because it indicates ischemia without an increase in myocardial oxygen demand. The ECG finding of ST-segment depression in leads V4 to V6 reflects subendocardial ischemia, not transmural injury, so STEMI is excluded. Because the high-sensitivity troponin remained below the upper reference limit on both the arrival sample and the 2-hour repeat, myocardial necrosis has not been detected, which rules out NSTEMI .

Key point! Unstable angina is defined by ischemic symptoms at rest or with minimal exertion, with or without ECG changes, but without biomarker evidence of myocardial necrosis. The absence of troponin elevation is what separates it from NSTEMI.

The distinction between unstable angina and stable angina rests on the pattern of symptoms. Stable angina is predictable, triggered by exertion or emotional stress, and relieved by rest or nitroglycerin. This patient’s pain began while resting at home and was not preceded by exertion, which makes stable angina unlikely. Vasospastic (variant) angina can also cause rest pain, but it typically produces transient ST-segment elevation during the episode, not ST-segment depression, and the ECG here shows depression in V4 to V6 .

Condition	Pain pattern	ECG finding	Troponin	Classification
Unstable angina	New, worsening, or rest pain	ST depression or T inversion possible	Normal	ACS without necrosis
NSTEMI	Rest or prolonged pain	ST depression or T inversion possible	Elevated	ACS with necrosis
STEMI	Rest or prolonged pain	ST elevation	Elevated	ACS with transmural necrosis
Stable angina	Predictable, exertional	Usually normal at rest	Normal	Chronic coronary disease

Watch out! A single normal troponin at arrival is not enough to exclude infarction. Serial testing is required because troponin release can be delayed. In this case, the repeat value at 2 hours was also normal with no significant change, which strengthens the classification as unstable angina rather than NSTEMI .

The pathophysiologic basis of unstable angina involves a disrupted atherosclerotic plaque with platelet aggregation and thrombus formation that partially occludes a coronary artery, reducing blood flow enough to cause ischemia but not persistent necrosis. The patient’s hypertension and daily smoking are major risk factors that accelerate endothelial injury and plaque instability. Unstable angina carries a substantial risk of progression to myocardial infarction or major adverse cardiac events, so prompt recognition and risk stratification in the emergency setting are essential .