Acute coronary syndrome (ACS) is one of the most time-critical emergencies in medicine: in STEMI, every 30 minutes of delay to primary PCI is associated with higher mortality. 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 1–2 h with a validated pathway |
| STEMI reperfusion target | First medical contact to device ≤90 min (≤120 min for transfers) |
| Fibrinolytic target | Door-to-needle ≤30 min when PCI cannot be achieved within 120 min of first medical contact |
| Oxygen threshold | Supplement only if SpO₂ <90%, to bring it to ≥90%; routine O₂ in normoxemic patients does not improve outcomes |
| Nitroglycerin hard stops | SBP <90 or >30 mmHg below baseline, suspected RV infarction, PDE-5 inhibitor use (24 h sildenafil / 48 h tadalafil) |
| Killip IV mortality | ~81% in the 1967 Killip series (about 40–50% in modern shock trials); needs urgent revascularization and hemodynamic support |
| Dual antiplatelet duration | Aspirin + P2Y12 inhibitor for 12 months by default; switching to ticagrelor alone after ≥1 month is an option to cut bleeding |
| Dressler syndrome window | Immune-mediated pericarditis weeks after MI; high-dose aspirin ± colchicine (avoid other NSAIDs and steroids) |
| Morphine caveat | IMPRESSION trial: morphine cut ticagrelor exposure by 36% and delayed its peak from 2 h to 4 h – 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 | New ST elevation at the J point in ≥2 contiguous leads (thresholds vary by lead, sex, and age – see STEMI criteria below) |
| Treatment urgency | Risk-stratify with TIMI or GRACE score; invasive or selective invasive approach | Immediate angiography if refractory angina or hemodynamic/electrical instability; within 24 h if high risk; before discharge otherwise | Emergent reperfusion – PCI within 90 min of first medical contact, or fibrinolysis within 30 min if PCI is delayed >120 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.
The mortality figures below are from the original 1967 Killip and Kimball series of 250 patients, and they remain the numbers quoted in nursing textbooks and on the NCLEX. In the modern reperfusion era, absolute mortality in every class is substantially lower – contemporary Class IV mortality runs closer to 40–50% than 81% – but the relative ranking between classes still holds, which is what makes the tool useful at the bedside.
| Killip class | Clinical findings | In-hospital mortality (1967 series) |
|---|---|---|
| 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 (2025 ACC/AHA ACS guideline). The first ECG is often nondiagnostic in NSTE-ACS, so a normal tracing does not rule out ACS: repeat it if symptoms persist or change, and rely on serial troponin.
STEMI criteria (Fourth Universal Definition of MI): new ST elevation at the J point in two contiguous leads, measured against thresholds that vary by lead, sex, and age:
- All leads except V2–V3: ≥1 mm
- V2–V3 in men aged ≥40: ≥2 mm
- V2–V3 in men under 40: ≥2.5 mm
- V2–V3 in women (any age): ≥1.5 mm
The frequently repeated “≥2 mm in the chest leads, ≥1 mm in the limb leads” shorthand over-calls elevation in women and young men and under-calls it in V1 and V4–V6. Use the lead-specific thresholds.
New LBBB is no longer a STEMI criterion. Older teaching treated new (or presumably new) left bundle branch block with ischemic symptoms as an automatic STEMI equivalent. That rule was removed from the 2013 ACCF/AHA STEMI guideline, and the 2025 ACC/AHA ACS guideline states that new or presumably new LBBB at presentation should not be considered diagnostic of acute MI in isolation – clinical correlation is required. New LBBB with chest pain remains a high-risk presentation: notify the provider immediately and apply Sgarbossa criteria (the Smith-modified proportional rule is more sensitive than the original) rather than assuming or excluding infarction on the block alone.
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 supports clinical decision pathways that draw hs-cTn at presentation (0 h) and again 1 to 2 hours later; the ESC 0/3-hour pathway is an alternative, and conventional assays need a repeat at 3–6 hours.
| 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 3–6 h; still used where hs assays are 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 Fourth Universal Definition requires a rise and/or fall of troponin with at least one value above the 99th-percentile upper reference limit (a change of more than 20% when the baseline is already elevated), plus clinical evidence of ischemia. 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; anticoagulation (heparin) is covered separately below.
Morphine – use selectively
Morphine (2–4 mg IV, repeated every 5–15 minutes if needed) reduces pain, anxiety, and sympathetic stimulation – which decreases heart rate and myocardial oxygen demand. The 2025 ACC/AHA guideline reserves it for pain that resists maximally tolerated anti-ischemic drugs and notes that it may delay the effects of oral P2Y12 therapy.
The controversy: The IMPRESSION trial (Kubica et al, 2016) randomized 70 MI patients receiving a 180 mg ticagrelor loading dose to 5 mg IV morphine or placebo. Morphine reduced total ticagrelor exposure by 36% and delayed peak concentration from 2 hours to 4 hours, with measurably higher platelet reactivity in the morphine group. The mechanism is delayed gastric emptying, which slows absorption of all oral P2Y12 inhibitors (ticagrelor, clopidogrel, prasugrel). Earlier observational work from the CRUSADE registry had already linked IV morphine in NSTEMI to higher adjusted in-hospital mortality. A 2-hour delay in peak antiplatelet effect falls in the critical window of STEMI management. Reserve morphine for pain that remains uncontrolled after nitroglycerin and position change. Monitor for hypotension and respiratory depression.
Oxygen – evidence-based threshold
The 2025 ACC/AHA guideline recommends supplemental oxygen only for confirmed hypoxia (SpO₂ <90%), titrated to bring saturation to 90% or higher, and recommends against routine oxygen when SpO₂ is 90% or above. The ESC 2023 ACS guideline uses the same 90% threshold. Some hospital protocols based on the BTS oxygen guideline start oxygen below 94%, so follow local policy.
The AVOID trial (2015) randomized 441 confirmed STEMI patients without hypoxia to oxygen at 8 L/min or no supplemental oxygen. Peak troponin (the primary measure) did not differ significantly, but peak CK was higher with oxygen, recurrent MI was more common (5.5% vs 0.9%), arrhythmias were more frequent (40.4% vs 31.4%), and infarct size on cardiac MRI at 6 months was larger (20.3 vs 13.1 g). The proposed mechanism: hyperoxia causes coronary vasoconstriction and increases oxidative stress. The larger DETO2X-AMI trial (6,629 patients with SpO₂ ≥90%) found no difference in 1-year mortality (5.0% vs 5.1%), which is why the guideline calls routine oxygen unhelpful in normoxemic patients.
Nitrates – rapid symptom relief
Sublingual nitroglycerin 0.3–0.4 mg every 5 minutes as needed, up to 3 doses, in hemodynamically stable patients with SBP ≥90 mmHg. Dilates coronary arteries and reduces preload through venodilation. IV nitroglycerin (starting at 10 mcg/min) is an option for persistent pain, hypertension, or pulmonary edema.
Hard contraindications:
- SBP <90 mmHg or a fall of more than 30 mmHg below baseline (further preload reduction risks hypotension and shock)
- Suspected 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 (use with great caution, if at all)
Aspirin – always first
Aspirin 162–325 mg, non-enteric-coated and chewed when possible to achieve a faster onset (2025 ACC/AHA guideline). Aspirin irreversibly inhibits platelet cyclooxygenase, blocking thromboxane A2 production and reducing platelet aggregation. It is the single most impactful early intervention: in ISIS-2, aspirin given within 24 hours of symptom onset reduced 5-week vascular mortality by about 23% (9.4% vs 11.8%), and aspirin combined with a fibrinolytic reduced it by 42%.
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 (2025 ACC/AHA list): acute heart failure (Killip class II–IV), a low-output state or high risk for cardiogenic shock, PR interval >0.24 s, second- or third-degree heart block without a pacemaker, severe bradycardia, and active bronchospasm. Start with a low oral dose and titrate as heart rate and blood pressure allow. The guideline does not support routine IV beta-blockers before primary PCI; in COMMIT, early IV then oral metoprolol reduced reinfarction and VF but increased cardiogenic shock, mainly in the first 24 hours.
Heparin – anticoagulation backbone
Anticoagulation is initiated with antiplatelet therapy to prevent thrombus propagation and reduce platelet activation at the reperfusion site.
- Unfractionated heparin (UFH): The class 1 anticoagulant for NSTE-ACS in the 2025 ACC/AHA guideline. Loading dose 60 units/kg (max 4,000 units), then 12 units/kg/h (max 1,000 units/h), titrated to an aPTT of 60–80 s (50–70 s with fibrinolytic therapy); reversal with protamine. Monitor aPTT every 6 hours until stable. Risk of heparin-induced thrombocytopenia (HIT) – check platelet count daily.
- Enoxaparin (LMWH): A recommended alternative to UFH in NSTE-ACS when an early invasive approach is not planned (fondaparinux is the other); 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.
System goal: first medical contact (FMC)-to-device ≤90 minutes for patients who arrive by EMS or walk in to a PCI-capable center; the traditional door-to-balloon metric uses the same 90-minute target.
Transfer patients: FMC-to-device ≤120 minutes – if a non-PCI hospital can get the patient to the cath lab within that window, transfer for primary PCI is recommended over fibrinolysis.
Nursing role in STEMI activation:
- Activate the catheterization lab immediately upon ECG confirmation – the guideline notes that each 30 minutes of delay to primary PCI is associated with higher mortality
- 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)
- Prepare the radial or femoral access site per operator preference (the 2025 ACC/AHA guideline recommends radial access to reduce bleeding and death)
- 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 cannot be achieved within 120 minutes of first medical contact, fibrinolytic therapy (also called thrombolytics) is the alternative. Examples: tenecteplase (TNK, single weight-based bolus of 30–50 mg), alteplase (tPA, 90-minute weight-based infusion), reteplase (rPA, two 10-unit boluses 30 minutes apart). Streptokinase is no longer available in the US.
Door-to-needle target: ≤30 minutes from ED arrival.
Fibrinolytic indication: STEMI symptom onset <12 hours and an anticipated delay to primary PCI of more than 120 minutes from FMC. Fibrinolytics are not given for ST depression alone unless true posterior STEMI is suspected.
Absolute contraindications (2025 ACC/AHA Table 14):
- Prior intracranial hemorrhage at any time
- Known structural cerebral vascular lesion
- Known malignant intracranial neoplasm
- Ischemic stroke within 3 months (except acute ischemic stroke being treated with thrombolysis)
- Significant closed-head or facial trauma within 3 months
- Intracranial or intraspinal surgery within 2 months
- Severe uncontrolled hypertension that does not respond to therapy (SBP >180 or DBP >110)
- Suspected aortic dissection
- Active bleeding or bleeding diathesis (excluding menses)
Selected relative contraindications: significant hypertension on presentation (SBP >180 or DBP >110) that does respond to treatment, chronic poorly controlled hypertension, ischemic stroke more than 3 months ago, dementia, traumatic or prolonged (>10 min) CPR, and major surgery within 3 weeks. These call for a risk-benefit decision by the provider rather than an automatic stop.
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. For elective CABG, the 2025 ACC/AHA guideline interrupts P2Y12 inhibitors for 3–5 days (ticagrelor), 5 days (clopidogrel), or 7 days (prasugrel); for urgent CABG, at least 24 hours of interruption is ideal and surgery may proceed sooner.
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 <90% = initiate supplemental O₂ |
| 3 | Administer aspirin 162–325 mg chewable immediately | Irreversible platelet inhibition; chewing a non-enteric-coated tablet speeds onset; give as early as possible |
| 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 <90% | 2025 ACC/AHA: give O₂ for SpO₂ <90% and titrate to ≥90%; routine O₂ in normoxemic patients does not improve outcomes (AVOID, DETO2X) |
| 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; given with aspirin (DAPT); ticagrelor may be crushed in water or given by NG tube if the patient cannot swallow; take clopidogrel without regard to food; avoid omeprazole and esomeprazole with clopidogrel (CYP2C19 inhibition reduces conversion to the active metabolite) – pantoprazole, lansoprazole, or rabeprazole are the preferred acid-suppression options |
| Anticoagulant – UFH | Unfractionated heparin | Potentiates antithrombin III → inhibits thrombin and factor Xa | Weight-based protocol (60 units/kg bolus, 12 units/kg/h); monitor aPTT q6h (target 60–80 s, or 50–70 s with fibrinolysis); 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; usually stopped 12–24 h before CABG |
| Anticoagulant – direct thrombin inhibitor | Bivalirudin (Angiomax) | Direct thrombin inhibition independent of antithrombin | An option 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 for acute HF, low-output state or shock risk, PR >0.24 s or high-grade AV block without a pacemaker, severe bradycardia, or active bronchospasm; do not abruptly discontinue; start low-dose oral within 24 h in stable patients (2025 ACC/AHA class 1); 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) | 3–5 days | Dyspnea (13.8% in PLATO vs 7.8% with clopidogrel; usually self-limiting); do not use with strong CYP3A4 inhibitors; avoid aspirin maintenance doses >100 mg/day (reduces ticagrelor efficacy); can be crushed if the patient cannot swallow |
| Prasugrel (Effient) | ~30 min (faster than clopidogrel) | Irreversible | ≥7 days | Contraindicated: active bleeding, prior stroke or TIA (boxed warning). Age ≥75: generally not recommended except in high-risk patients (diabetes or prior MI). Weight <60 kg: higher bleeding risk, consider the 5 mg maintenance dose |
| Clopidogrel (Plavix) | About 2–6 h after a 600 mg load; 3–7 days to full effect on 75 mg daily without a load | Irreversible | ≥5 days | Requires hepatic conversion to active metabolite (CYP2C19); about 2% of White, 4% of Black, and 14% of Chinese patients are poor metabolizers (boxed warning: consider another P2Y12 inhibitor), and roughly a third more carry one reduced-function allele; concurrent omeprazole or esomeprazole reduces efficacy – use pantoprazole, lansoprazole, or rabeprazole instead (ranitidine, the older alternative, was withdrawn from the US market in 2020) |
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: emergency revascularization of the culprit vessel (in CULPRIT-SHOCK, culprit-only PCI beat immediate multivessel PCI, 30-day death or kidney replacement 45.9% vs 55.4%); norepinephrine as the usual first vasopressor (in SOAP II, dopamine caused more arrhythmias overall and was linked to higher 28-day mortality in the cardiogenic shock subgroup); dobutamine for inotropic support. In selected STEMI patients with severe or refractory shock, a microaxial flow pump (Impella CP) is reasonable to reduce death (DanGer Shock), at the cost of more bleeding, limb ischemia, and kidney injury. Routine IABP or VA-ECMO is not recommended (IABP-SHOCK II, no survival benefit).
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. For a quick reference on distinguishing all four AV block types and their nursing priorities, see the heart block poem.
- 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 1 mg IV (2025 AHA ACLS dose), repeated every 3–5 minutes to a 3 mg maximum; 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, which usually has a single blood supply from the posterior descending artery (RCA in most people); the anterolateral muscle has a dual supply from the LAD and circumflex. 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. It is now rare (0.1–0.5% in the reperfusion era) and usually transient. Treatment per the 2025 ACC/AHA guideline: conservative care and acetaminophen; high-dose aspirin if symptoms persist.
Dressler syndrome (weeks after MI, classically 2–8 weeks): An immune-mediated reaction to pericardial injury, including any degree of hemopericardium. Features include fever, pleuritic chest pain, pericardial effusion, and elevated inflammatory markers (ESR, CRP, WBC). Treatment: high-dose aspirin (500–1,000 mg every 6–8 hours until symptoms improve) plus colchicine 0.5–0.6 mg once or twice daily for 3 months. Glucocorticoids and NSAIDs other than aspirin are potentially harmful after MI because they may impair myocardial healing and raise the risk of rupture and recurrent MI.
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 involving the LAD, LVEF <30%, or late reperfusion. Its incidence in the PCI era is under 5–10%. Echocardiography is the first-line test (cardiac MRI if echo is inconclusive). Most patients receive about 3 months of anticoagulation (warfarin or a DOAC) on top of antiplatelet therapy, then repeat imaging; the bleeding risk of triple therapy has to be weighed against embolic risk.
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, usually for 12 months; the cardiologist may switch to a single drug earlier to reduce bleeding, but never stop either drug on your own, because 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: the 2025 ACC/AHA guideline (class 1) says every ACS patient should be referred to an outpatient program before discharge, to reduce death, MI, and readmissions and to improve function and quality of life
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: The IMPRESSION trial demonstrated that morphine delays gastric emptying and significantly slows absorption of oral P2Y12 inhibitors, including ticagrelor – reducing ticagrelor exposure by 36% and delaying peak concentration by 2 hours. 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 the dose is not adjusted, but the provider should be aware of the pharmacokinetic interaction. Crushing is not required: the label allows crushed tablets in water (or via NG tube) for patients who cannot swallow, but it is not mandatory for every patient.
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 hs-troponin pathways of 0/1–2 h (the 2025 ACC/AHA approach) and 0/3 h are both validated – a fixed 6-hour wait is older, conventional-assay 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 is immune-mediated and occurs weeks after MI, so day 3 is too early. 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
- MONA mnemonic: what it means and when to use it – detailed breakdown of each component with current evidence
- EKG interpretation cheat sheet – rhythm identification, intervals, and arrhythmia recognition
- Heart failure nursing reference – HFrEF vs HFpEF, NYHA classification, and post-MI heart failure management
- Atrial fibrillation nursing reference – AF complicating ACS: rate control, anticoagulation, cardioversion
- Hypertension nursing reference – blood pressure targets, antihypertensive classes, hypertensive crisis
- Nursing lab values cheat sheet – troponin, BNP, coagulation studies, and electrolyte reference ranges
- Electrolyte imbalances reference – potassium and magnesium monitoring in cardiac patients
- ABG interpretation – respiratory and metabolic disturbances in cardiogenic shock
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