Initial Treatment for Myocardial Infarction
Immediately administer aspirin 160-325 mg (chewable or water-soluble), provide oxygen if the patient is breathless, give sublingual nitroglycerin (unless systolic BP <90 mmHg or heart rate <50 or >100 bpm), administer intravenous morphine 4-8 mg for pain relief with an antiemetic, obtain a 12-lead ECG within 10 minutes, and initiate reperfusion therapy (thrombolysis or primary PCI) within 90 minutes of first medical contact if ST-elevation or new left bundle branch block is present. 1
Time-Critical Initial Actions
The first 60 minutes after symptom onset are absolutely critical—thrombolytic therapy given within the first hour saves 65 lives per 1000 patients treated, compared to only 25 lives per 1000 when given at 4-6 hours. 2 This dramatic difference in mortality benefit makes every minute count.
Immediate Medication Administration (Within Minutes)
Aspirin 160-325 mg orally should be given immediately, preferably chewable or water-soluble formulation for faster absorption. 2, 1 This reduces mortality in acute MI and should not be delayed while awaiting definitive diagnosis. 1
Oxygen via nasal prongs is recommended, especially for patients who are breathless or have signs of heart failure. 2, 1
Sublingual nitroglycerin should be administered unless systolic blood pressure is <90 mmHg or heart rate is <50 or >100 bpm. 1
Intravenous morphine 4-8 mg (or diamorphine) is essential for adequate analgesia, with additional 2 mg doses at 5-minute intervals until pain relief is achieved. 2, 1 This is not merely for comfort—adequate analgesia reduces sympathetic activation and decreases cardiac workload. 1
Antiemetics must be administered concurrently with opioids to prevent nausea and vomiting. 2, 1
Diagnostic Assessment (Within 10 Minutes)
12-lead ECG should be obtained within 10 minutes of arrival to identify ST-segment elevation (≥1 mV) in contiguous leads or new left bundle branch block. 1 The American College of Cardiology recommends that evaluation be completed within 10 minutes of emergency department arrival, with no more than 20 minutes elapsing before assessment. 1
Continuous cardiac monitoring should be established immediately to detect life-threatening arrhythmias, which are most common in the first 24 hours. 1
Emergency resuscitation equipment, including a defibrillator, must be immediately available. All patients with chest pain require an emergency response with a vehicle containing a defibrillator and staff trained in its use. 2, 1
Reperfusion Therapy (Target: Within 90 Minutes)
Patients with obvious acute myocardial infarction should receive thrombolytic treatment (in the absence of contraindications) within 90 minutes of alerting the medical or paramedical service (the "call to needle time"). 2 While 90 minutes is a reasonable target, 60 minutes is ideal. 1
Thrombolytic Therapy
Thrombolytic therapy (fibrinolysis) is most beneficial when given within the first hour, saving 65 lives per 1000 patients treated, compared to 27 lives per 1000 in the second or third hour, and only 25 lives per 1000 at 4-6 hours. 2, 1
The American College of Cardiology recommends immediate reperfusion therapy for patients with ST-elevation MI or new LBBB, with greatest benefit when initiated within 6 hours of symptom onset. 1
Heparin administration may be beneficial with thrombolytic therapy, particularly with tissue plasminogen activator. 1 For patients with large anterior MI or left ventricular mural thrombus, early intravenous heparin may reduce stroke risk. 1
Primary PCI Alternative
- Primary percutaneous transluminal coronary angioplasty (PTCA) is an alternative to thrombolysis if performed in a timely fashion by skilled personnel with access to emergency CABG. 1
Additional Medications to Have Available
Beyond the immediate medications, the following drugs should be readily available: 2
- Adrenaline (epinephrine)
- Atropine
- Lignocaine (lidocaine)
- Frusemide (furosemide)
- Naloxone
Beta-Blocker Administration (Early Phase)
For hemodynamically stable patients with definite or suspected acute MI, intravenous metoprolol can be initiated as soon as the patient's clinical condition allows. 3 The protocol involves three bolus injections of 5 mg each at approximately 2-minute intervals, with continuous monitoring of blood pressure, heart rate, and ECG. 3 Patients who tolerate the full 15 mg IV dose should begin oral metoprolol 50 mg every 6 hours, starting 15 minutes after the last IV dose. 3
Critical Pitfalls to Avoid
Delaying ECG assessment beyond 10 minutes of arrival is unacceptable. 1
Withholding aspirin while waiting for definitive diagnosis—aspirin should be given immediately based on clinical suspicion. 1
Administering thrombolytics to patients without ST-elevation or with contraindications. 1 Note that elderly patients (>65 years), those with low body weight (<70 kg), hypertension, or receiving tissue plasminogen activator have increased risk of intracranial hemorrhage. 1
Failing to provide adequate analgesia, which increases sympathetic activation and worsens cardiac workload. 1
Delaying reperfusion therapy—the benefit is time-dependent with greatest advantage in the first hour after symptom onset. 1
Administering nitroglycerin to hypotensive patients (systolic BP <90 mmHg) or those with extreme heart rates (<50 or >100 bpm). 1
System-Level Considerations
The entire healthcare system must be coordinated to achieve rapid treatment: 2
- Ambulance services should have defibrillators and trained staff
- General practitioners should have protocols for rapid response with oxygen, aspirin, and nitrates readily available
- Hospitals should implement "fast tracking" for patients with obvious MI
- Direct communication between ambulance and admitting hospital should be established