Contents
The ACS Spectrum
- Unstable angina: ischemia, NO troponin rise
- NSTEMI: troponin rise WITHOUT ST elevation (often ST depression/T inversion)
- STEMI: troponin rise WITH ST elevation — full-thickness, time-critical
- All represent acute myocardial ischemia from plaque rupture and thrombus
Pathophysiology
- Atherosclerotic plaque ruptures → platelet aggregation → coronary thrombus
- Partial occlusion = UA/NSTEMI; complete occlusion = STEMI
- Ischemia → injury → infarction if flow is not restored
- "Time is muscle" — reperfusion speed determines outcome
Presentation
- Chest pressure/pain, often radiating to arm/jaw, with diaphoresis, dyspnea, nausea
- Atypical presentations in women, elderly, and diabetics (fatigue, SOB)
- Get a 12-lead ECG within 10 minutes of arrival
- Assess for hemodynamic instability and arrhythmia
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Start Free Practice →ECG Localization
- Inferior: II, III, aVF (right coronary artery)
- Anterior/septal: V1–V4 (LAD)
- Lateral: I, aVL, V5–V6 (circumflex)
- Inferior MI: get a right-sided ECG — RV involvement makes nitro dangerous (preload-dependent)
Cardiac Biomarkers
- Troponin is the most specific marker; rises 3–6 hr, peaks ~12–24 hr
- Serial troponins establish the trend
- A normal troponin does not exclude unstable angina
- Correlate biomarkers with ECG and symptoms
Initial Management
- Aspirin (chewed) early unless contraindicated
- Antiplatelet (P2Y₁₂ inhibitor) + anticoagulation per protocol
- Nitroglycerin for pain/ischemia — AVOID in RV infarct, hypotension, or recent PDE-5 inhibitor use
- Oxygen only if SpO₂ <90%; morphine for refractory pain; statin
Reperfusion Strategy
- STEMI: emergent PCI is preferred — door-to-balloon ≤90 min
- If PCI unavailable in time: fibrinolytics within 30 min (door-to-needle), if no contraindications
- NSTEMI/UA: risk-stratify; early invasive (angiography) for high risk
- Know absolute fibrinolytic contraindications (prior ICH, active bleeding, recent stroke, etc.)
Post-MI Complications
- Arrhythmias: VTach/VFib (leading early cause of death), heart block (esp. inferior MI)
- Cardiogenic shock: large infarct → pump failure
- Mechanical: papillary muscle rupture (acute MR), VSD, free-wall rupture
- Heart failure, pericarditis (Dressler), reinfarction
Key Medications (longer term)
- Dual antiplatelet therapy (aspirin + P2Y₁₂ inhibitor)
- Beta-blocker (reduces myocardial O₂ demand) unless contraindicated
- ACE inhibitor and high-intensity statin
- Anticoagulation during the acute phase per protocol
Nursing Priorities
- Continuous ECG monitoring; treat arrhythmias promptly
- Serial troponins, pain assessment, and hemodynamic monitoring
- Prepare for cath lab; minimize door-to-balloon time
- Patient education: medication adherence, risk-factor modification, cardiac rehab
Can you answer these 3 CCRN questions?
Here are 3 questions in the style of our premium bank. The full rationale explains exactly why the right answer is right — and why the distractors trap most test-takers.
Premium Practice Question
A patient with an inferior STEMI (II, III, aVF) becomes hypotensive after sublingual nitroglycerin. The most likely explanation is:
- Anaphylaxis to nitroglycerin
- Right ventricular infarction with preload dependence
- Pulmonary embolism
- Aortic dissection
Rationale: Inferior STEMIs frequently involve the right ventricle, which is preload dependent; nitroglycerin reduces preload and can cause profound hypotension....
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Premium Practice Question
A patient arrives with a STEMI to a PCI-capable center. The priority goal is:
- Door-to-needle time under 30 minutes
- Door-to-balloon time under 90 minutes
- Administer fibrinolytics immediately
- Obtain serial troponins before any treatment
Rationale: For STEMI at a PCI-capable facility, emergent percutaneous coronary intervention with a door-to-balloon time of 90 minutes or less is the preferred reperfusion strategy....
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Premium Practice Question
Which ECG leads correspond to an anterior wall MI?
- II, III, aVF
- V1–V4
- I, aVL, V5–V6
- V7–V9
Rationale: Anterior/septal MIs from LAD occlusion produce ST changes in the precordial leads V1 through V4....
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Related CCRN Guides
Frequently Asked Questions
What is the difference between unstable angina, NSTEMI, and STEMI?
Unstable angina is ischemia without a troponin rise. NSTEMI is myocardial infarction with a troponin rise but without ST-segment elevation. STEMI is a full-thickness infarction with ST elevation, usually from complete coronary occlusion, and is the most time-critical.
What is the goal door-to-balloon time for STEMI?
For STEMI at a PCI-capable center, the goal is a door-to-balloon time of 90 minutes or less. If PCI is not available in time, fibrinolytics should be given with a door-to-needle time of 30 minutes or less, provided there are no contraindications.
Why is nitroglycerin dangerous in an inferior or right ventricular MI?
Right ventricular infarction (which often accompanies inferior MI) is preload dependent. Nitroglycerin reduces preload and can cause severe hypotension, so it should be avoided and a right-sided ECG obtained.
How is the location of an MI identified on ECG?
Inferior MIs show changes in II, III, and aVF (right coronary artery); anterior/septal MIs in V1–V4 (LAD); and lateral MIs in I, aVL, V5, and V6 (circumflex).
What is the most common cause of early death after an MI?
Lethal ventricular arrhythmias such as ventricular fibrillation are the leading early cause of death, which is why continuous ECG monitoring is essential.
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