What is the treatment for myocardial infarction (heart attack)?

Treatment of Myocardial Infarction

The treatment of myocardial infarction requires immediate reperfusion therapy within 90 minutes of first medical contact, along with aspirin, oxygen, nitroglycerin, and adequate analgesia to reduce mortality and improve outcomes. 1, 2

Initial Emergency Assessment and Management

• Evaluation should be completed within 10 minutes of arrival to the emergency department, with no more than 20 minutes elapsing before assessment 1
• A 12-lead ECG should be obtained immediately to identify ST-segment elevation (≥1mV) in contiguous leads or new left bundle branch block, which indicates need for reperfusion therapy 1, 2
• Initial management should include:
  • Oxygen administration via nasal prongs 1, 2
  • Sublingual nitroglycerin (unless systolic BP <90mmHg or heart rate <50 or >100bpm) 1, 2
  • Aspirin 160-325mg orally (chewable for faster absorption) 1, 2
  • Adequate analgesia with intravenous morphine (4-8mg initially with additional doses as needed) or diamorphine, with concurrent antiemetics 1, 2
• Continuous cardiac monitoring should be established immediately with emergency resuscitation equipment readily available 1

Reperfusion Strategy

• Immediate reperfusion therapy is essential for patients with ST-elevation MI or new LBBB 2, 1

• The greatest benefit occurs when reperfusion is initiated within the first hour after symptom onset (65 lives saved per 1000 patients treated) 2, 1

• Two main reperfusion options exist:

  1. Thrombolytic therapy (fibrinolysis):

     • Most beneficial when given within the first hour (35 lives saved per 1000 patients) compared to 7-12 hours (16 lives saved per 1000) 2, 1
     • Options include tissue plasminogen activator, streptokinase, or urokinase 3
     • Consider for patients who cannot receive timely PCI 2

  2. Primary Percutaneous Coronary Intervention (PCI):

     • Preferred if it can be performed within 90 minutes by skilled personnel with access to emergency CABG 2, 4
     • More effective than thrombolysis when performed in a timely manner 4

• The "call to needle time" should ideally be no longer than 60 minutes, with 90 minutes as a reasonable target 2, 1

• Delayed reperfusion beyond 90 minutes increases mortality four-fold in rural STEMI patients 5

Pharmacological Management

Immediate Medications

• Aspirin 160-325mg reduces mortality and should be administered immediately 1, 2
• Intravenous opioids (morphine 4-8mg or diamorphine) with antiemetics are essential for pain relief 1, 2
• Nitroglycerin for chest pain relief and to reduce preload 1, 2

Early Adjunctive Therapy

• Beta-blockers (e.g., metoprolol) should be initiated early in hemodynamically stable patients 6
  • For metoprolol: three bolus injections of 5mg IV at 2-minute intervals, followed by oral therapy 6
• ACE inhibitors (e.g., lisinopril) should be started within 24 hours of MI onset, particularly for anterior MI or LV dysfunction 7, 8
  • Lisinopril has been shown to reduce mortality by 11% when started within 24 hours 7
• Anticoagulation with heparin should be considered, particularly for patients with large anterior MI who are at high risk for LV mural thrombus 2, 4

Monitoring and Management After First 24 Hours

• Monitor for complications including arrhythmias, heart failure, and mechanical complications 2
• For patients with significant left ventricular damage, bedrest is recommended for the first 12-24 hours 2
• Echocardiography should be performed to evaluate LV function and detect complications such as mural thrombus 4
• Continue aspirin indefinitely 4
• Continue beta-blockers for at least 6 weeks 4
• For patients with LV dysfunction or anterior MI, continue ACE inhibitors 7
• Strict glycemic control in diabetic patients using insulin-glucose infusion followed by multiple-dose insulin treatment reduces long-term mortality 2

Special Considerations

• Elderly patients (>65 years), those with low body weight (<70kg), hypertension, or receiving tissue plasminogen activator have increased risk of intracranial hemorrhage with thrombolytic therapy 2
• Patients with anterior MI are at higher risk for left ventricular dysfunction and heart failure 4
• For patients with intraventricular thrombi, especially if mobile or protuberant, anticoagulation with heparin followed by oral anticoagulants for 3-6 months is recommended 2

Common Pitfalls to Avoid

• Delaying ECG assessment beyond 10 minutes of arrival 1
• Withholding aspirin administration while waiting for definitive diagnosis 1
• Administering thrombolytics to patients without ST-elevation or with contraindications 1
• Failing to provide adequate analgesia, which can increase sympathetic activation 1
• Delaying reperfusion therapy, as benefit is time-dependent with greatest advantage in the first hour 2, 5
• Overlooking the need for continuous cardiac monitoring in the first 24 hours when arrhythmias are most common 1