STEMI vs NSTEMI: what the ECG and troponin tell the nurse

The deciding finding: ST elevation on the 12 lead ECG

MSD Manuals defines STEMI as myocardial necrosis with ST segment elevation in two contiguous leads, reflecting injury through the full thickness of the heart wall. Because this finding drives emergency treatment, the ECG should be performed as soon as possible after arrival, within 10 minutes, so the team can decide on reperfusion.

In NSTEMI the ECG shows no ST elevation. It may show ST depression or T wave inversion, or it may look unremarkable. NSTEMI is confirmed when troponin rises above the reference limit in the right clinical setting, and it typically reflects damage to the inner layer of the heart muscle rather than its full thickness.

Overlapping findings and what troponin can and cannot tell you

Chest pain or pressure, shortness of breath, sweating, nausea and anxiety occur in both, and some patients have milder or atypical symptoms. Symptom severity cannot tell the nurse whether a patient has a STEMI or an NSTEMI, and neither can the patient's appearance on arrival.

Troponin rises in both, and it lags behind the start of injury, so an early normal result does not exclude infarction and is repeated over time. MSD Manuals stresses that a normal first troponin should not delay STEMI treatment. Troponin confirms NSTEMI; it does not decide whether a STEMI patient goes for reperfusion.

Nursing priorities in STEMI

Time to reperfusion drives everything. The nurse obtains or confirms the 12 lead ECG, alerts the team through the local STEMI pathway, starts continuous cardiac monitoring, establishes intravenous access and gives ordered medicines such as aspirin and nitroglycerin, checking blood pressure before nitroglycerin. With inferior ST elevation, expect a right-sided ECG, because right ventricular involvement makes the patient preload dependent and nitroglycerin can cause severe hypotension. Oxygen is given if saturation is low.

Primary percutaneous coronary intervention is preferred when it can be done promptly; fibrinolytic medicine is used when timely PCI is not available. The nurse prepares the patient for the catheter laboratory, or screens for bleeding risk before fibrinolysis, and watches closely for arrhythmias, hypotension and signs of heart failure.

Nursing priorities in NSTEMI

Patients with NSTEMI are treated with antiplatelet and anticoagulant therapy, and the team uses risk scores to decide how soon angiography happens. Fibrinolytics are not used, because they have not shown benefit in NSTEMI and may increase risk. The nurse draws serial troponins on schedule and repeats the ECG if pain returns or changes.

Ongoing or recurrent chest pain, new ECG changes, arrhythmias, hypotension or signs of heart failure raise a patient's risk and need immediate escalation. The nurse monitors for bleeding while anticoagulants run, keeps the patient on cardiac monitoring, and supports rest, pain relief and anxiety reduction as ordered.

Hypothetical practice scenario

Hypothetical scenario, not a real exam item: a client arrives with crushing chest pain. The 12 lead ECG shows ST elevation in leads II, III and aVF, and the first troponin result is within the normal range. Which action is best: wait for a repeat troponin before calling cardiology, activate the STEMI pathway, or book a stress test?

Activating the STEMI pathway is correct, because ST elevation on the ECG triggers reperfusion without waiting for biomarkers. Waiting for a repeat troponin is the tempting distractor, since troponin lags behind injury and delay costs heart muscle. A stress test is inappropriate during a suspected acute infarction.

Sources and further reading

MSD Manual Professional Version: Overview of Acute Coronary Syndromes. Definitions of unstable angina, NSTEMI and STEMI, ECG within 10 minutes, serial troponin, PCI preferred with fibrinolysis as fallback, and why fibrinolytics are avoided in NSTEMI.

NHLBI: Heart Attack Diagnosis. ECG as the first test within minutes of arrival and troponin blood tests repeated over time.

NHLBI: Heart Attack Treatment. Aspirin, nitroglycerin, oxygen when levels are low, thrombolytic medicines when timely intervention is unavailable, and PCI.