6.2 Acute Coronary Syndromes in ACLS
Key Takeaways
- The ACS algorithm starts with a 12-lead ECG within 10 minutes of arrival to classify STEMI, NSTEMI, or unstable angina.
- Give chewable aspirin 162-325 mg early unless truly contraindicated; it reduces mortality in ACS.
- For STEMI, reperfusion goals are first-medical-contact-to-balloon (PCI) at most 90 minutes, or door-to-needle for fibrinolysis at most 30 minutes.
- Oxygen is not automatic; give it only when SpO2 is below 90% or there is dyspnea/distress.
- Nitroglycerin relieves ischemic pain but is withheld in hypotension, RV infarction, or recent PDE-5 inhibitor use; morphine is for refractory pain.
6.2 The Acute Coronary Syndromes Algorithm
Acute coronary syndrome (ACS) spans ST-elevation MI (STEMI), non-ST-elevation MI (NSTEMI), and unstable angina. The ACLS ACS algorithm exists to recognize ischemia fast, start protective therapy, and route STEMI to reperfusion before more myocardium dies. Tested symptoms include chest pressure or discomfort radiating to the arm or jaw, dyspnea, diaphoresis, nausea, and syncope; women, older adults, and patients with diabetes more often have atypical or silent presentations, so a normal-appearing patient does not exclude ACS.
The algorithm steps
- EMS/triage: monitor, support ABCs, prepare to defibrillate, and obtain a 12-lead ECG within 10 minutes of first medical contact or ED arrival.
- Immediate general treatments (the classic memory aids, applied with judgment):
- Aspirin 162-325 mg chewed (non-enteric preferred) unless there is true allergy or active bleeding. This is the single most important early drug for mortality reduction.
- Nitroglycerin sublingual or spray for ongoing ischemic pain.
- Oxygen only if SpO2 < 90% or the patient is dyspneic, hypoxemic, or in distress; routine oxygen for normoxic patients offers no benefit and may harm.
- Morphine for chest pain unresponsive to nitroglycerin (use cautiously; it can mask symptoms and lower blood pressure).
- Classify by the 12-lead ECG into STEMI (ST elevation or new LBBB), NSTEMI/high-risk unstable angina (ST depression or dynamic T-wave changes), or normal/nondiagnostic ECG with low-to-intermediate risk.
Nitroglycerin cautions
Withhold nitroglycerin if SBP < 90 mmHg or 30 mmHg below baseline, with heart rate < 50 or > 100, with suspected right ventricular (inferior) infarction (preload-dependent), or within 24-48 hours of a phosphodiesterase-5 inhibitor (sildenafil 24 h, tadalafil 48 h) because the combination causes profound, refractory hypotension.
Reperfusion time goals for STEMI
STEMI is a time-critical diagnosis. The whole system is built to shorten ischemic time.
| Reperfusion pathway | Goal | Notes |
|---|---|---|
| Primary PCI (preferred) | First-medical-contact-to-device <= 90 min | <= 120 min if transferred from a non-PCI hospital |
| Door-to-balloon (PCI hospital) | <= 90 min | Activate the cath lab early from the field 12-lead |
| Fibrinolysis (when PCI unavailable in time) | Door-to-needle <= 30 min | For STEMI within 12 h of onset, no contraindications |
Fibrinolytics carry bleeding risk; absolute contraindications include any prior intracranial hemorrhage, ischemic stroke within 3 months, known intracranial neoplasm or AV malformation, active bleeding, and suspected aortic dissection. When a patient cannot reach a PCI center within the window, prehospital or door-to-needle fibrinolysis within 30 minutes is the alternative.
Link to post-arrest care
A post-ROSC 12-lead showing STEMI mandates emergent angiography. Even without ST elevation, recurrent ventricular arrhythmias, hemodynamic shock, or electrical instability should trigger cardiology activation because an occluded coronary artery may be the cause of the arrest.
Common traps
- Giving oxygen to every ACS patient regardless of saturation; reserve it for SpO2 < 90% or distress.
- Forgetting or delaying aspirin, or using an enteric-coated tablet that absorbs slowly.
- Giving nitroglycerin in inferior/RV infarction, hypotension, or after a PDE-5 inhibitor.
- Assuming the absence of chest pain rules out ACS in diabetic or older patients.
Scenario anchor
A 58-year-old with crushing chest pain gets a field 12-lead showing 3 mm anterior ST elevation. EMS gives aspirin 324 mg chewed, holds nitroglycerin because the SBP is 88 mmHg, transmits the ECG, and pre-activates the cath lab so first-medical-contact-to-balloon stays under 90 minutes.
Reading the 12-Lead and Risk-Stratifying
STEMI is defined by new ST-segment elevation in two or more anatomically contiguous leads (or a new left bundle branch block in the right clinical setting). Knowing the territory helps anticipate complications.
| ECG leads with ST elevation | Wall / artery | Watch for |
|---|---|---|
| II, III, aVF | Inferior / right coronary artery | RV involvement, bradycardia, nitroglycerin-induced hypotension |
| V1-V4 | Anterior / left anterior descending | Pump failure, large infarct, heart block |
| I, aVL, V5-V6 | Lateral / left circumflex | - |
| V4R | Right ventricle | Preload-dependent; give fluids, avoid nitrates |
An inferior STEMI should prompt a right-sided lead (V4R) to detect RV infarction, which is why nitroglycerin is dangerous in this setting.
Beyond the immediate four drugs
After aspirin, definitive ACS therapy (started in concert with cardiology) commonly adds a second antiplatelet agent (P2Y12 inhibitor such as clopidogrel, ticagrelor, or prasugrel**)**, an anticoagulant (heparin), beta-blockers (when not contraindicated by heart failure, bradycardia, or hypotension), statins, and an ACE inhibitor. These are not part of the first 1-2 minutes of the ACLS algorithm but define the in-hospital pathway the algorithm hands off to.
NSTEMI and unstable angina
When the ECG shows ST depression or dynamic T-wave inversion (not elevation), the patient has NSTEMI or unstable angina. These patients are not candidates for fibrinolytics and are managed with antiplatelet/anticoagulant therapy and risk-stratified for an early invasive (angiography) versus ischemia-guided strategy based on troponin, ongoing symptoms, hemodynamics, and risk scores. The ACLS algorithm's job is to recognize the non-STEMI ACS group, start aspirin and supportive care, and admit for cardiology management rather than rushing to the cath lab in the first minutes.
Quick recap
- 12-lead within 10 minutes classifies the patient.
- Aspirin 162-325 mg early for nearly everyone.
- STEMI -> reperfusion clock (PCI <= 90 min, lytics <= 30 min).
- NSTEMI/UA -> antithrombotics + risk-based invasive timing, no lytics.
A STEMI patient presents to a PCI-capable hospital. Per the ACS algorithm, the target door-to-balloon (first-device) time is at most:
Which medication should be given earliest to most ACS patients because it reduces mortality?
A patient with inferior STEMI has an SBP of 86 mmHg and took sildenafil 6 hours ago. Which immediate ACS treatment should be WITHHELD?