Acute coronary syndrome (ACS) kills more Americans than any other cardiac emergency. Every nurse working in an ED, telemetry unit, ICU, or step-down setting will manage these patients — and the quality of that nursing care directly determines whether the patient survives, retains cardiac function, or develops preventable complications.
This reference covers the full ACS spectrum: pathophysiology, ECG interpretation, biomarker timing, MONA/MONAB protocol with current evidence updates, reperfusion targets, pharmacology, post-MI complications, and patient education. Use it alongside the MONA mnemonic, the EKG interpretation cheat sheet, and the heart failure nursing reference.
Fast-scan summary: ACS key facts
| Domain | Key fact |
|---|---|
| First medication to give | Aspirin 162–325 mg chewable — before anything else |
| Gold-standard biomarker | High-sensitivity troponin I or T; serial draws at 0 h and 3 h |
| STEMI reperfusion target | Door-to-balloon ≤90 min (primary PCI) |
| Fibrinolytic target | Door-to-needle ≤30 min when PCI not available within 120 min |
| Oxygen threshold | Supplement only if SpO₂ <94% — routine O₂ increases infarct size |
| Nitroglycerin hard stops | SBP <90, RV infarction, PDE-5 inhibitor use (24 h sildenafil / 48 h tadalafil) |
| Killip IV mortality | ~81% — cardiogenic shock; needs vasopressors + urgent revascularization |
| Dual antiplatelet duration | Aspirin + P2Y12 inhibitor for ≥12 months post-ACS |
| Dressler syndrome window | Autoimmune pericarditis 2–8 weeks post-MI; treat with NSAIDs + colchicine |
| Morphine caveat | CRISP-AMI data: morphine delays P2Y12 absorption by up to 2 hours — use selectively |
ACS spectrum: UA, NSTEMI, and STEMI compared
All three ACS subtypes share the same trigger — atherosclerotic plaque disruption leading to coronary thrombus — but differ in the degree and duration of coronary occlusion.
| Feature | Unstable angina (UA) | NSTEMI | STEMI |
|---|---|---|---|
| Coronary occlusion | Partial or transient | Partial or intermittent, with some collateral flow | Complete and persistent |
| Myocardial necrosis | No (ischemia only) | Yes — subendocardial | Yes — transmural (full-thickness) |
| Troponin | Normal | Elevated, rising or falling pattern | Elevated |
| ECG findings | ST depression, T-wave inversion, or normal | ST depression, T-wave inversion, or nonspecific | ST elevation ≥2 mm in ≥2 contiguous leads, or new LBBB |
| Treatment urgency | Medical management; risk-stratify with TIMI or GRACE score | Medical management; catheterization within 24–48 h (or emergent if unstable/high-risk) | Emergent reperfusion — PCI within 90 min or fibrinolysis within 30 min |
| Short-term mortality | Low | Moderate (similar long-term outcome to STEMI) | Highest short-term mortality |
Pathophysiology: plaque to infarction
Plaque rupture and thrombus formation
Atherosclerotic plaques containing a large lipid core and thin fibrous cap are most prone to rupture. When mechanical stress or inflammation causes plaque disruption, the exposed subendothelial collagen and lipid core activate the clotting cascade. Platelets adhere, aggregate, and degranulate — releasing thromboxane A2 and ADP, which recruit more platelets. Fibrin forms around the platelet plug, creating an occlusive thrombus within minutes.
Zones of ischemia and infarction
As coronary blood flow falls, three concentric zones develop in the affected territory:
- Zone of ischemia (outer ring): viable but hypoperfused cells; ECG shows T-wave changes; recovers with reperfusion
- Zone of injury (middle ring): injured cells still alive; ECG shows ST changes; may recover if reperfusion is fast enough
- Zone of necrosis (innermost core): dead myocardium; ECG shows Q waves; does not recover
The goal of all reperfusion strategies is to salvage the injury zone before it converts to necrosis.
Infarction patterns
Subendocardial infarction (NSTEMI): necrosis limited to the inner third of the myocardium, which has the highest oxygen demand and lowest perfusion pressure. No ST elevation on ECG. Troponin elevated.
Transmural infarction (STEMI): necrosis extending through the full wall thickness. ST elevation in leads corresponding to the affected territory. Q waves develop over hours to days.
Clinical presentation
Classic symptoms
The cardinal symptom of MI is substernal chest pain described as crushing, squeezing, pressure, or tightness — often radiated to the left arm, jaw, neck, or epigastrium. Diaphoresis, dyspnea, nausea, and pallor typically accompany it. The pain lasts more than 20 minutes and is not relieved by rest or nitroglycerin.
Atypical presentations — commonly tested, clinically critical
A significant proportion of MI patients — particularly women, elderly patients, and those with diabetes — do not present with classic crushing chest pain. Missing these presentations is a leading cause of delayed diagnosis.
| Population | Atypical presentation pattern | Why it happens |
|---|---|---|
| Women | Dyspnea, fatigue, nausea, back or jaw pain; may have no chest pain at all | Hormonal differences; more likely to have microvascular disease and type 2 MI |
| Elderly patients | Dyspnea as primary symptom; confusion, syncope, generalized weakness | Reduced pain perception; comorbidities mask the clinical picture |
| Diabetic patients | "Silent MI" — minimal or no chest pain; fatigue or shortness of breath | Autonomic neuropathy blunts afferent pain signaling |
Nursing implication: Any combination of diaphoresis, unexplained dyspnea, nausea, and new fatigue in a patient with cardiac risk factors warrants a stat 12-lead ECG and troponin — regardless of whether chest pain is present.
Killip classification: bedside risk stratification
The Killip classification requires no imaging — only auscultation, observation, and blood pressure. It quantifies the degree of left ventricular failure on arrival and predicts short-term mortality.
| Killip class | Clinical findings | Approximate in-hospital mortality |
|---|---|---|
| Class I | No signs of heart failure — clear lungs, no S3 gallop | ~6% |
| Class II | Mild heart failure — bibasilar rales (bottom <50% of lung fields), S3 gallop, or JVD | ~17% |
| Class III | Pulmonary edema — rales in more than half of lung fields | ~38% |
| Class IV | Cardiogenic shock — SBP <90 mmHg with signs of end-organ hypoperfusion (oliguria, altered mentation, cool extremities) | ~81% |
Reassess Killip class with every vital sign check. Deterioration from Class I to Class II demands immediate escalation.
Diagnostic workup
ECG: the most important initial test
A 12-lead ECG must be obtained and interpreted within 10 minutes of arrival. ECG sensitivity for MI is only about 30% — a normal ECG does not rule out ACS — but specificity is 95–97%, making ST elevation a reliable action trigger.
STEMI criteria: ST elevation ≥2 mm in two or more contiguous precordial leads, or ≥1 mm in two or more limb leads, or a new left bundle branch block (LBBB) in a patient with ischemic symptoms.
ECG changes by phase:
- Hyperacute T waves (minutes): tall, peaked, broad-based T waves — the earliest sign, often missed
- ST elevation (minutes to hours): indicates active transmural injury
- T-wave inversion (hours to days): evolves as injury zone cools
- Pathological Q waves (hours to days, permanent): electrically silent dead tissue
Coronary territories and corresponding leads:
| Affected wall | ECG leads | Culprit artery | Clinical note |
|---|---|---|---|
| Anterior | V1–V4 | LAD (left anterior descending) | Largest LV territory; highest mortality; watch for complete heart block and cardiogenic shock |
| Lateral | I, aVL, V5–V6 | Left circumflex (LCx) | Often silent; may present with atypical symptoms |
| Inferior | II, III, aVF | RCA (right coronary artery) | Always check right-sided leads (V3R–V6R) for RV involvement — changes fluid strategy |
| Posterior | Tall R wave, ST depression in V1–V2 | RCA or LCx | Reciprocal changes only — look for ST elevation in posterior leads (V7–V9) |
| Right ventricle | ST elevation in V3R–V6R | Proximal RCA | Preload-dependent — give IV fluids, avoid nitroglycerin and morphine |
See the EKG interpretation cheat sheet for rhythm identification, intervals, and bundle branch block criteria.
Cardiac biomarkers
High-sensitivity troponin I (hs-cTnI) or troponin T (hs-cTnT) is the biomarker of choice. The 2025 ACC/AHA guideline recommends serial troponin at 0 and 3 hours (or 0 and 1 hour with validated high-sensitivity assays).
| Biomarker | Rise | Peak | Normalized | Notes |
|---|---|---|---|---|
| hs-Troponin I/T | 1–3 h | 12–24 h | 5–14 days | Gold standard; most sensitive and specific; a rising-and-falling delta pattern confirms acute MI |
| Conventional troponin | 3–6 h | 12–24 h | 5–14 days | Serial at 0 and 6 h; still used where hs assays unavailable |
| CK-MB | 3–8 h | 12–24 h | 48–72 h | Returns to normal faster — useful for detecting reinfarction; less specific than troponin |
| Myoglobin | 1–3 h | 6–9 h | 12–24 h | Rises earliest; nonspecific (also elevated in skeletal muscle injury) |
| BNP / NT-proBNP | Hours | Variable | Days | Reflects ventricular wall stress; elevated in heart failure complicating MI; see heart failure nursing |
Nursing considerations: A single troponin measurement cannot diagnose or rule out MI. The serial delta — a rise of ≥20% or an absolute rise above the 99th-percentile threshold — is the diagnostic criterion. Troponin is also elevated in PE, sepsis, myocarditis, renal failure, and atrial fibrillation with rapid ventricular response; clinical context determines the diagnosis.
Imaging
- Echocardiogram: Identifies wall motion abnormalities (regional hypokinesis, akinesis, or dyskinesis) corresponding to the ischemic territory; assesses ejection fraction; detects mechanical complications
- Chest X-ray: Evaluates for pulmonary edema, cardiomegaly, mediastinal widening
- Coronary angiography: Gold standard for identifying the culprit lesion; performed during primary PCI
MONA/MONAB protocol: current evidence
The MONA mnemonic (Morphine, Oxygen, Nitrates, Aspirin) provides the framework for initial ACS management. Current guidelines have significantly updated how each component is applied. The MONAB extension adds Beta-blockers and heparin (H) to the acute management sequence.
Morphine — use selectively
Morphine (2–4 mg IV in small increments) reduces pain, anxiety, and sympathetic stimulation — which decreases heart rate and myocardial oxygen demand. However, morphine is no longer a routine first-line agent.
The controversy: The CRISP-AMI study and OACIS registry data demonstrated that morphine delays gastric emptying and significantly slows absorption of oral P2Y12 inhibitors (ticagrelor, clopidogrel, prasugrel). In patients receiving a P2Y12 loading dose, morphine administration delayed peak antiplatelet effect by 1–2 hours — a critical window in STEMI management. Reserve morphine for pain that remains uncontrolled after nitroglycerin and position change. Monitor for hypotension and respiratory depression.
Oxygen — evidence-based threshold
Supplemental oxygen should be administered only if SpO₂ falls below 94% (some institutions use <90% per older guidelines — follow your institution’s protocol).
The AVOID trial (2015) randomized STEMI patients to high-flow oxygen (8 L/min) versus no supplemental oxygen in normoxemic patients. The oxygen group had a significantly larger infarct size at 30 days on cardiac MRI, higher rates of recurrent MI, and higher rates of AF. The proposed mechanism: hyperoxia causes coronary vasoconstriction and increases oxidative stress, worsening ischemia. The 2025 ACC/AHA guideline reflects this evidence — routine oxygen for normoxemic ACS patients is not recommended.
Nitrates — rapid symptom relief
Sublingual nitroglycerin 0.4 mg every 5 minutes, up to 3 doses. Dilates coronary arteries and reduces preload through venodilation.
Hard contraindications:
- SBP <90 mmHg (further preload reduction risks hypotension and shock)
- Right ventricular infarction (RV is preload-dependent; nitroglycerin can precipitate hemodynamic collapse)
- Recent PDE-5 inhibitor use: sildenafil (Viagra) within 24 hours; tadalafil (Cialis) within 48 hours — combined effect causes severe hypotension
- Severe aortic stenosis
Aspirin — always first
Aspirin 162–325 mg chewable (not swallowed whole — chewing increases absorption by 50%). Aspirin irreversibly inhibits platelet cyclooxygenase, blocking thromboxane A2 production and reducing platelet aggregation. It is the single most impactful early intervention: administering aspirin within the first hour of MI reduces mortality by approximately 23% (ISIS-2 trial).
Beta-blockers — early oral, not routine IV
Oral beta-blockers (metoprolol succinate or carvedilol) are initiated within the first 24 hours in hemodynamically stable patients without contraindications. They reduce heart rate and contractility, decreasing myocardial oxygen demand, and suppress ventricular arrhythmias.
Contraindications to early beta-blocker in ACS: HR <60, SBP <100 mmHg, signs of heart failure or cardiogenic shock, significant PR prolongation (>0.24 s), reactive airway disease. The 2025 ACC/AHA guideline does not support routine IV beta-blocker administration for STEMI (the COMMIT trial data showed no mortality benefit and increased cardiogenic shock risk with early IV use in unselected patients).
Heparin — anticoagulation backbone
Anticoagulation is initiated with antiplatelet therapy to prevent thrombus propagation and reduce platelet activation at the reperfusion site.
- Unfractionated heparin (UFH): Weight-based IV bolus plus infusion; flexible titration; reversal with protamine. Monitor aPTT every 6 hours. Risk of heparin-induced thrombocytopenia (HIT) — check platelet count daily.
- Enoxaparin (LMWR): Preferred in NSTEMI; more predictable pharmacokinetics; no routine aPTT monitoring; renally cleared (adjust dose for CrCl <30).
- Bivalirudin: A direct thrombin inhibitor; preferred when HIT history is present or HIT is suspected. Short half-life (~25 min); easily reversed by stopping infusion.
Reperfusion strategies
Primary PCI: door-to-balloon time
Primary percutaneous coronary intervention (PCI) is the preferred reperfusion strategy for STEMI when available. A catheter is advanced through the coronary arteries to the occlusion site; balloon inflation opens the vessel, and a stent is deployed to maintain patency.
Door-to-balloon (D2B) target: ≤90 minutes from ED arrival at a PCI-capable center.
First medical contact-to-device time: ≤120 minutes — including transfer time if the patient presents at a non-PCI facility.
Nursing role in STEMI activation:
- Activate the catheterization lab immediately upon ECG confirmation — every 10 minutes saved translates to measurable mortality reduction
- Establish two large-bore IV lines (18-gauge or larger)
- Draw stat labs: hs-troponin, CBC, BMP, coagulation studies (PT/INR, aPTT), lipid panel, type and screen
- Administer aspirin + P2Y12 inhibitor loading dose as ordered (see pharmacology table)
- Administer IV anticoagulation per protocol (UFH, enoxaparin, or bivalirudin)
- Confirm allergy history (contrast dye, iodine, latex)
- Obtain pre-procedure weight (critical for weight-based heparin dosing)
- Mark radial or femoral access site per operator preference (2025 ACC/AHA guideline recommends radial-first approach for reduced bleeding and mortality)
- Brief patient and family: consent, expected procedure duration, post-procedure monitoring
- Continue continuous cardiac monitoring en route to the cath lab
Reperfusion arrhythmias: After balloon inflation and vessel opening, expect accelerated idioventricular rhythm (AIVR) — a wide-complex, regular rhythm at 40–100 bpm. AIVR is a sign of successful reperfusion and is typically self-limiting; it does not require treatment. Ventricular fibrillation can also occur at reperfusion — keep defibrillator immediately accessible.
Fibrinolytic therapy: door-to-needle time
When primary PCI is not available within 120 minutes of first medical contact, fibrinolytic therapy (also called thrombolytics) is the alternative. Examples: tenecteplase (TNK), alteplase (tPA), reteplase (rPA).
Door-to-needle target: ≤30 minutes from ED arrival.
Fibrinolytic indication: STEMI symptom onset <12 hours, cannot achieve PCI within 120 min.
Absolute contraindications:
- Prior intracranial hemorrhage at any time
- Known structural cerebral vascular lesion
- Known malignant intracranial neoplasm
- Ischemic stroke within 3 months
- Significant closed-head or facial trauma within 3 months
- Intracranial or intraspinal surgery within 2 months
- Severe, uncontrolled hypertension (SBP >180 or DBP >110 on presentation)
- Suspected aortic dissection
- Active bleeding or bleeding diathesis
Nursing monitoring post-fibrinolysis: Q15-min vital signs and neuro checks for the first hour. Signs of failed reperfusion or reocclusion: return of chest pain, re-elevation of ST segments, hemodynamic deterioration — notify provider immediately; rescue PCI may be required. Monitor all puncture sites for bleeding. Do not perform IM injections after fibrinolytic administration.
CABG considerations
Coronary artery bypass grafting (CABG) is considered when coronary anatomy is not suitable for PCI (e.g., left main disease, severe three-vessel disease). In acute STEMI, surgery is deferred until hemodynamic stabilization unless mechanical complications (e.g., papillary muscle rupture, VSD) require emergent intervention. P2Y12 inhibitors must be held before CABG — ticagrelor for ≥5 days, clopidogrel ≥5 days, prasugrel ≥7 days.
Nursing interventions: priority-ordered
| Priority | Intervention | Rationale / key parameters |
|---|---|---|
| 1 | Continuous 12-lead ECG monitoring with ST-segment trending | Detect new ST changes indicating reocclusion or extension; detect reperfusion arrhythmias; alert threshold: ST change >1 mm from baseline |
| 2 | Vital signs q15 min during acute phase; continuous SpO₂ | Catch early hemodynamic deterioration; SBP <90 = escalate immediately; SpO₂ <94% = initiate supplemental O₂ |
| 3 | Administer aspirin 162–325 mg chewable immediately | Irreversible platelet inhibition; chewing increases speed of absorption; give before nitroglycerin |
| 4 | 12-lead ECG within 10 minutes of arrival | Identify STEMI pattern requiring emergent cath lab activation; time-to-ECG is a quality metric |
| 5 | Two large-bore IVs (18-gauge or larger) with blood draws | One line for medications; one for contrast/fluids during procedure; draw hs-troponin, CBC, BMP, coags, lipids, type and screen |
| 6 | Administer nitroglycerin SL 0.4 mg q5 min × 3 (if no contraindications) | Relieves ischemic pain, reduces preload; HOLD for SBP <90, RV infarction, or recent PDE-5 inhibitor |
| 7 | Supplemental oxygen only if SpO₂ <94% | AVOID trial: routine O₂ in normoxemic patients increases infarct size; titrate to SpO₂ 94–99% |
| 8 | Pain reassessment after each intervention (0–10 scale) | Persistent or worsening pain suggests ongoing ischemia, reocclusion, or inadequate reperfusion — escalate |
| 9 | Position in semi-Fowler's (30–45°) | Reduces preload, improves respiratory mechanics; do not place flat unless hemodynamically required |
| 10 | Strict intake/output; daily weights | Monitor for early heart failure; urine output <30 mL/h for 2 consecutive hours = notify provider |
| 11 | Enforce bed rest for first 12–24 h; activity progression per protocol | Reduces myocardial O₂ demand during vulnerable period; gradual mobilization thereafter |
| 12 | Monitor vascular access site post-PCI | Radial: assess for radial artery occlusion, compartment syndrome; femoral: assess for hematoma, retroperitoneal bleeding; check pulses, Doppler if needed |
Pharmacology reference table
| Drug / class | Examples | Mechanism | Nursing considerations |
|---|---|---|---|
| Antiplatelet — COX inhibitor | Aspirin 81–325 mg | Irreversible COX-1 inhibition → blocks thromboxane A2 → reduces platelet aggregation | Loading dose 162–325 mg chewable; maintenance 81 mg daily; hold before non-cardiac surgery >7 days; GI bleeding risk — administer with food for maintenance |
| Antiplatelet — P2Y12 inhibitor | Ticagrelor (Brilinta), clopidogrel (Plavix), prasugrel (Effient) | Block platelet ADP receptor P2Y12 → reduce platelet activation and aggregation | See P2Y12 comparison below; always given with aspirin (DAPT); do not crush ticagrelor; take clopidogrel without regard to food; do not take with proton pump inhibitors (reduces clopidogrel efficacy) |
| Anticoagulant — UFH | Unfractionated heparin | Potentiates antithrombin III → inhibits thrombin and factor Xa | Weight-based protocol; monitor aPTT q6h (therapeutic: 60–100 s); platelet count daily (HIT risk); reverse with protamine sulfate; HIT: 4T score screening |
| Anticoagulant — LMWH | Enoxaparin (Lovenox) | Primarily anti-Xa activity; more predictable pharmacokinetics than UFH | Renally cleared: reduce dose for CrCl <30; no routine aPTT monitoring; anti-Xa level if renal impairment or obesity; do not give within 12 h before CABG |
| Anticoagulant — direct thrombin inhibitor | Bivalirudin (Angiomax) | Direct thrombin inhibition independent of antithrombin | Preferred in HIT history; short half-life ~25 min; renal dosing for CrCl <30; no specific reversal agent |
| Beta-blocker | Metoprolol succinate, carvedilol | β1 blockade → reduces HR, contractility, and myocardial O₂ demand; antiarrhythmic | Hold if HR <60, SBP <100, active bronchospasm, or cardiogenic shock; do not abruptly discontinue; start oral within 24 h in stable patients; carvedilol also has α1 blockade (more BP lowering) |
| ACE inhibitor | Lisinopril, enalapril, ramipril | Inhibit angiotensin-converting enzyme → reduce angiotensin II → prevent adverse cardiac remodeling | Start within 24 h if SBP ≥100 and no cardiogenic shock; monitor K⁺ and creatinine; hold for bilateral renal artery stenosis; switch to ARB if ACEi-induced cough |
| ARB | Valsartan, losartan | Block angiotensin II AT1 receptor — same downstream effect as ACEi without bradykinin-mediated cough | Use when ACEi is contraindicated or not tolerated; same renal and potassium monitoring applies |
| Statin | Atorvastatin 80 mg, rosuvastatin 20–40 mg | HMG-CoA reductase inhibitor → reduces LDL synthesis; plaque stabilization independent of LDL lowering | High-intensity statin initiated immediately post-ACS regardless of baseline LDL; monitor LFTs at baseline; myopathy risk — check CK if muscle pain; check drug interactions (CYP3A4) |
| Nitrate | Nitroglycerin SL, IV NTG, isosorbide mononitrate | Nitric oxide donor → venodilation (preload ↓) and coronary vasodilation | Tolerance develops with continuous exposure — use nitrate-free period for long-acting forms; hold for SBP <90, RV MI, or PDE-5 inhibitor use; IV NTG: titrate by symptom and BP |
| Aldosterone antagonist | Eplerenone, spironolactone | Block mineralocorticoid receptor → reduce fibrosis and adverse remodeling; mild diuresis | Use post-MI with EF ≤40% and HF or diabetes; contraindicated if K⁺ >5 mEq/L or CrCl <30; monitor K⁺ closely — hyperkalemia risk with concurrent ACEi/ARB; see heart failure nursing |
P2Y12 inhibitor comparison: a commonly tested distinction
All three agents block the platelet P2Y12 receptor but differ significantly in onset, reversibility, and contraindications:
| Drug | Onset | Reversibility | Hold before CABG | Key contraindications / cautions |
|---|---|---|---|---|
| Ticagrelor (Brilinta) | ~30 min | Reversible (non-covalent binding) | ≥5 days | Dyspnea (in ~14% — a direct drug effect, not pulmonary); do not use with strong CYP3A4 inhibitors; avoid aspirin doses >100 mg/day (reduces ticagrelor efficacy) |
| Prasugrel (Effient) | ~30 min (faster than clopidogrel) | Irreversible | ≥7 days | Contraindicated: prior stroke or TIA (net harm in clinical trials); age >75 (increased bleeding; use only if high-risk features present); body weight <60 kg |
| Clopidogrel (Plavix) | 2–6 h; peak at 3–7 days with standard dosing | Irreversible | ≥5 days | Requires hepatic conversion to active metabolite (CYP2C19); ~20–30% of patients are poor metabolizers (reduced efficacy); concurrent omeprazole reduces efficacy — use pantoprazole or ranitidine instead |
Post-MI complications
Cardiogenic shock
Cardiogenic shock (Killip Class IV) occurs in 5–8% of STEMIs, most commonly following anterior wall infarction destroying >40% of LV mass. Hemodynamic profile: SBP <90 mmHg, cardiac index <2.2 L/min/m², PCWP >18 mmHg. Treatment: norepinephrine or dopamine for vasopressor support; dobutamine for inotropic support; intra-aortic balloon pump (IABP) or microaxial flow device (Impella) for mechanical circulatory support; urgent revascularization.
Arrhythmias
- Ventricular fibrillation (VF) / ventricular tachycardia (VT): Peak risk in the first 4 hours; defibrillator must be at the bedside. Persistent VT/VF after reperfusion may require amiodarone.
- Accelerated idioventricular rhythm (AIVR): Wide-complex rhythm at 40–100 bpm; sign of reperfusion; self-limiting, no treatment required. Distinguish from VT (rate 100+, hemodynamically unstable).
- Complete heart block: More common in inferior MI (RCA supplies the AV node in 85% of people); may require transcutaneous pacing urgently. Watch for new PR prolongation progressing to Mobitz II or 3rd-degree block.
- Atrial fibrillation: Occurs in 10–15% of MI patients; increases stroke risk; see atrial fibrillation nursing reference for management.
- Bradycardia / sinus arrest: Common with inferior MI; atropine 0.5–1 mg IV first-line; transcutaneous pacing if refractory.
Mechanical complications (1–7 days post-MI)
These are rare but rapidly fatal without surgical intervention:
- Ventricular septal rupture: New loud holosystolic murmur radiating to the sternum + acute hemodynamic deterioration. Diagnosis by echo. Emergent CABG + VSR repair.
- Papillary muscle rupture: Causes acute severe mitral regurgitation — new apical systolic murmur + flash pulmonary edema. Most often involves the posteromedial papillary muscle (supplied by the RCA alone; anterolateral is supplied by two arteries). Emergent mitral valve surgery.
- Left ventricular free wall rupture: Sudden PEA cardiac arrest. Almost universally fatal without emergent surgery. Subacute variety (false aneurysm) may have time for surgical repair.
Pericarditis and Dressler syndrome
Early post-MI pericarditis (days 1–3): Direct inflammation of the pericardium overlying the infarcted zone. Pain is sharp, pleuritic, and positional — worsens when supine, improves sitting forward. Pericardial friction rub on auscultation. Treatment: NSAIDs; avoid anticoagulation adjustment if clinically stable.
Dressler syndrome (2–8 weeks post-MI): An autoimmune reaction — the immune system generates antibodies against injured cardiac tissue released during infarction. Features include fever, pleuritic chest pain, pericardial effusion, and elevated inflammatory markers (ESR, CRP, WBC). Treatment: NSAIDs (ibuprofen or aspirin) plus colchicine; corticosteroids for refractory cases.
Key distinction for NCLEX: Reinfarction produces pressure-type chest pain, new ECG ST elevation, and rising troponin. Pericarditis/Dressler produces sharp, positional, pleuritic pain, a friction rub, and diffuse (not regional) ST elevation or PR depression. The clinical context and ECG pattern differentiate them.
Left ventricular thrombus and stroke
LV thrombus forms in areas of akinetic or dyskinetic myocardium — most commonly after anterior STEMI with large wall motion abnormality. Anticoagulation with warfarin or direct oral anticoagulants (in addition to DAPT) is recommended when LV thrombus is identified on echocardiogram.
Heart failure post-MI
Large infarctions, especially anterior, reduce ejection fraction and initiate the neurohormonal cascade of heart failure — activating the renin-angiotensin-aldosterone system and sympathetic nervous system. Early initiation of ACEi/ARB, beta-blocker, and aldosterone antagonist reduces adverse remodeling and long-term mortality. Refer to the heart failure nursing reference for management after the acute phase.
Patient education before discharge
Effective discharge education is essential — most preventable readmissions follow medication non-adherence or failure to recognize warning signs.
Medications — what to tell patients:
- Take dual antiplatelet therapy (aspirin + P2Y12 inhibitor) every day for at least 12 months; stopping early can cause stent thrombosis, which is life-threatening
- Take the statin even if cholesterol feels “controlled” — statins stabilize plaque and reduce future events
- Do not stop beta-blockers or ACE inhibitors without calling the cardiologist
- Nitroglycerin: take one tablet SL; call 911 if no relief in 5 minutes — do not take three tablets and then drive
Lifestyle modifications:
- Smoking cessation is the most impactful single change; offer pharmacotherapy (varenicline, nicotine replacement) before discharge
- Cardiac diet: Mediterranean-style; reduce saturated fat, sodium, and processed foods; weight management targeting BMI <30
- Moderate-intensity exercise: target 150 minutes per week after completing cardiac rehab
- Cardiac rehabilitation: enrollment is recommended for all post-MI patients and is associated with a ~25% reduction in all-cause mortality and reduced readmission
Hypertension management: Home BP target <130/80 per 2025 AHA/ACC hypertension guideline.
When to call 911: Teach patients to call 911 — not drive — for: chest pain or pressure lasting >5 minutes not relieved by nitroglycerin, new or worsening shortness of breath at rest, sudden severe dizziness, or pain radiating to the arm, jaw, or back. Emphasize that atypical symptoms (fatigue, nausea, back pain) are also valid reasons to call.
Follow-up:
- Cardiology within 1–2 weeks of discharge
- Repeat lipid panel at 4–8 weeks
- Repeat echocardiogram at 6–12 weeks to reassess ejection fraction
- Check lab values for BMP (K⁺, creatinine) within 1–2 weeks of starting ACEi/ARB or aldosterone antagonist
NCLEX practice questions
Question 1
A patient arrives to the ED with crushing substernal chest pain and diaphoresis. The nurse’s first priority action is:
A) Administer morphine 4 mg IV for pain relief B) Obtain a 12-lead ECG within 10 minutes C) Draw troponin and CBC D) Establish IV access
Answer: B
Rationale: The 12-lead ECG is the single most important initial diagnostic action in suspected ACS and must be obtained within 10 minutes of arrival. It identifies a STEMI pattern requiring immediate cath lab activation — every minute of delay increases myocardial death. IV access and labs are critical but follow ECG confirmation. Morphine is not a first-line agent and is given only for refractory pain after nitroglycerin.
Question 2
A patient with inferior STEMI has a blood pressure of 88/54 mmHg and clear lung fields. Which order should the nurse question?
A) Normal saline 500 mL IV bolus B) Sublingual nitroglycerin 0.4 mg C) Aspirin 325 mg chewable D) 12-lead ECG with right-sided leads
Answer: B
Rationale: Right ventricular infarction commonly accompanies inferior MI (the RCA supplies the RV in most patients). The RV is preload-dependent — nitroglycerin causes venodilation and reduces preload, which can precipitate severe hemodynamic collapse in this setting. The nurse should question the nitroglycerin order and confirm right-sided lead results first. Normal saline bolus is appropriate (RV infarction requires volume), aspirin is indicated in all ACS, and right-sided leads are essential to diagnose RV involvement.
Question 3
A patient with STEMI received tenecteplase 45 minutes ago. The nurse notes the patient now has no chest pain, the ST segments have returned to baseline, and there is an accelerated idioventricular rhythm at 70 bpm on the monitor. What is the most appropriate nursing response?
A) Prepare for immediate defibrillation B) Administer amiodarone 150 mg IV C) Document findings and continue monitoring — this is an expected response to reperfusion D) Notify the provider of a new hemodynamically significant arrhythmia
Answer: C
Rationale: Accelerated idioventricular rhythm (AIVR) is a benign reperfusion arrhythmia occurring when the ischemic tissue repolarizes and becomes the dominant pacemaker briefly. The rate is 40–100 bpm, it is hemodynamically stable, and it requires no treatment. Combined with ST resolution and pain relief, AIVR confirms successful thrombolysis. Defibrillation and amiodarone are reserved for hemodynamically unstable VT (rate >100) or VF.
Question 4
A nurse is preparing to administer a loading dose of ticagrelor 180 mg PO to a STEMI patient who is also receiving IV morphine for chest pain. Which consideration is most clinically significant?
A) Ticagrelor must be crushed for faster absorption B) Morphine may delay ticagrelor absorption, reducing early antiplatelet effect C) Ticagrelor is contraindicated in patients who have received morphine D) The loading dose should be reduced if morphine has been given
Answer: B
Rationale: CRISP-AMI and OACIS registry data demonstrate that morphine delays gastric emptying and significantly slows absorption of oral P2Y12 inhibitors, including ticagrelor. This is a clinically important interaction in the acute STEMI window when early platelet inhibition is critical for PCI success. Ticagrelor is not contraindicated with morphine and should not be crushed (no clinical benefit and may affect enteric coating). The dose is not adjusted, but the provider should be aware of the pharmacokinetic interaction.
Question 5
A 68-year-old woman presents with three days of intermittent fatigue, nausea, and jaw discomfort. Her ECG shows new T-wave inversions in V1–V4. Troponin drawn 3 hours ago was 0.04 ng/mL (reference <0.04); a repeat troponin drawn now is 0.19 ng/mL. What is the correct interpretation?
A) This is an incidental troponin elevation — the ECG changes are nonspecific and the patient is low-risk B) This represents a rising troponin delta consistent with NSTEMI C) STEMI diagnosis requires ST elevation; this ECG pattern rules it out D) Serial troponin is only valid if drawn exactly 6 hours apart
Answer: B
Rationale: A rising troponin delta — an absolute rise from below (0.04) to above (0.19) the 99th-percentile threshold on serial draws — meets diagnostic criteria for myocardial infarction. Combined with new ischemic ECG changes (T-wave inversions in V1–V4, suggesting anterior ischemia), this is an NSTEMI. STEMI requires ST elevation; NSTEMI is defined by troponin rise without ST elevation. The presentation is classic of a woman presenting atypically (fatigue, nausea, jaw pain). Serial troponin intervals of 0/3 h or 0/1 h (with hs assays) are both validated — the 6-hour protocol is older guidance.
Question 6
A patient returns from primary PCI for anterior STEMI and develops sharp, positional chest pain on day 3. The pain worsens when lying flat and improves when leaning forward. Temperature is 38.2°C. ECG shows diffuse ST elevation with PR depression. Which complication does this presentation indicate?
A) Stent thrombosis and reinfarction B) Left ventricular free wall rupture C) Early post-MI pericarditis D) Dressler syndrome
Answer: C
Rationale: This is early post-MI pericarditis — inflammation of the pericardium adjacent to infarcted tissue, typically occurring days 1–3 post-MI. The hallmark features are present: sharp pleuritic pain positional in nature (worse supine, better leaning forward), low-grade fever, and diffuse ST elevation with PR depression on ECG. Dressler syndrome presents with the same mechanism but occurs 2–8 weeks post-MI (too early here). Reinfarction would produce pressure-type chest pain, new regional ST elevation in the infarct territory, and rising troponin. Free wall rupture presents as sudden PEA arrest, not gradual onset of positional pain.
Related resources
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