What is the optimal treatment window for acute myocardial infarction (AMI)?

Optimal Treatment Window for Acute Myocardial Infarction

Reperfusion therapy is indicated in all patients with symptoms of ischemia of ≤12 hours duration and persistent ST-segment elevation, with primary PCI being the preferred strategy when performed by an experienced team within 120 minutes of STEMI diagnosis. 1, 2

Primary Treatment Windows

• Reperfusion therapy should be initiated as soon as possible after symptom onset, with the greatest benefit observed within the first hours 1
• A powerful time-dependent effect on mortality has been observed with thrombolytic therapy, with 35 lives saved per 1000 patients when used within the first hour compared to 16 lives saved per 1000 when given 7-12 hours after symptom onset 1
• For primary PCI, the following time targets should be met:
  • First medical contact (FMC) to ECG and diagnosis: ≤10 minutes 1, 2
  • FMC to fibrinolysis ("door to needle"): ≤30 minutes 1, 2
  • FMC to primary PCI ("door to balloon") in PCI-capable hospitals: ≤60 minutes 1, 2
  • FMC to primary PCI in transferred patients: ≤90 minutes (≤120 minutes if early presenter with large area at risk) 1, 2

Reperfusion Strategy Based on Time Windows

Within 12 Hours of Symptom Onset

• Primary PCI is the preferred reperfusion strategy when performed by an experienced team within 120 minutes of STEMI diagnosis 1, 2
• If primary PCI cannot be performed in a timely manner, fibrinolytic therapy should be administered within 12 hours of symptom onset in patients without contraindications 1
• Fibrinolytic therapy should be initiated as soon as possible, preferably in the pre-hospital setting 1, 2
• The benefit of fibrinolytic therapy is greatest when administered within the first 2-3 hours after symptom onset 1

12-24 Hours After Symptom Onset

• Primary PCI may be considered in stable patients presenting 12-24 hours after symptom onset 1, 3
• Reperfusion therapy (preferably primary PCI) is indicated if there is evidence of ongoing ischemia, even if symptoms started >12 hours before or if pain and ECG changes have been stuttering 1, 2
• A randomized study demonstrated myocardial salvage and improved 4-year survival with primary PCI compared to conservative treatment in patients without persistent symptoms 12-48 hours after symptom onset 1, 3

Beyond 24 Hours After Symptom Onset

• Routine PCI of a totally occluded artery >24 hours after symptom onset in stable patients without signs of ischemia is not recommended 1
• In asymptomatic patients, routine PCI of an occluded infarct-related artery >48 hours after onset of STEMI is not indicated 1

Adjunctive Therapies

• Aspirin (160-325 mg orally or IV if unable to swallow) should be administered as soon as possible 1, 2
• A potent P2Y12 inhibitor (prasugrel or ticagrelor, or clopidogrel if these are unavailable) should be administered before or at the time of PCI 1, 2
• Anticoagulation is recommended during primary PCI with unfractionated heparin 1, 2
• For patients receiving fibrinolytic therapy, anticoagulation should be continued until revascularization or for the duration of hospital stay up to 8 days 1, 2

Special Considerations

• The PCI-related delay that may mitigate the benefit of mechanical intervention over fibrinolysis varies between 60 and 120 minutes 1
• The acceptable PCI-related delay may vary according to age, symptom duration, and infarct location - from <1 hour for anterior infarction in patients <65 years presenting <2 hours after symptom onset, to almost 3 hours for non-anterior infarction in patients >65 years presenting >2 hours after symptom onset 1
• Recent meta-analyses suggest that late PCI (>12 hours but not 2-60 days after symptom onset) may still provide clinical benefit compared to medical therapy alone 4
• Emergency angiography and PCI are indicated in patients with heart failure/shock regardless of time from symptom onset 1, 2

Common Pitfalls and Caveats

• Delaying reperfusion therapy beyond the optimal window significantly reduces myocardial salvage and increases mortality 1
• Failure to recognize STEMI in patients with atypical symptoms or non-diagnostic initial ECGs can lead to treatment delays 2
• Overestimating the contraindications to fibrinolytic therapy when primary PCI is not readily available 1, 2
• Not considering primary PCI in patients presenting 12-24 hours after symptom onset, especially with evidence of ongoing ischemia 1, 3
• Performing routine PCI of totally occluded arteries beyond 24 hours in stable patients without evidence of ischemia, which provides no clinical benefit 1