Acute Myocardial Infarction (AMI) and its ECG Diagnosis

Introduction

Acute Myocardial Infarction (AMI), commonly known as a heart attack, occurs when there is a sudden blockage of blood flow to the heart muscle. This blockage is usually due to a blood clot forming within a coronary artery that is already narrowed by atherosclerosis.

The timely diagnosis of AMI is critical, and one of the most important tools used for this is the Electrocardiogram (ECG). Let's discuss how ECG changes help in diagnosing AMI.

Key ECG Features of Acute Myocardial Infarction

ECG changes in AMI depend on the severity and timing of the infarction. The main findings include:

1. ST-Segment Elevation (STEMI)

• Hallmark of acute MI due to total artery occlusion.
• Seen as an elevation of the ST segment in at least two contiguous leads.
• Localizes the infarct to a specific heart region:
  • Anterior MI (leads V1-V4) → Left anterior descending artery occlusion.
  • Inferior MI (leads II, III, aVF) → Right coronary artery occlusion.
  • Lateral MI (leads I, aVL, V5-V6) → Circumflex artery occlusion.

2. ST-Segment Depression and T-wave Inversion (NSTEMI or Ischemia)

• Indicates subendocardial ischemia (partial obstruction of the artery).
• Non-ST Elevation Myocardial Infarction (NSTEMI) is diagnosed if cardiac biomarkers like troponins are elevated in addition to ST depressions/T-wave inversions.

3. Pathologic Q Waves

• Develop hours to days after infarction.
• Sign of previous or evolving MI, indicating irreversible myocardial damage.

4. Hyperacute T-waves

• Early sign of infarction before ST elevation occurs.
• Seen as tall, peaked T-waves in affected leads.

5. Reciprocal Changes

• ST-segment depression in leads opposite to the infarcted area (e.g., inferior ST elevation in II, III, aVF may show reciprocal depression in leads I, aVL).

Importance of Early Diagnosis and Management

• Early recognition of ECG changes is crucial in guiding rapid treatment such as thrombolysis or primary percutaneous coronary intervention (PCI).
• Time is muscle – the earlier the intervention, the better the heart muscle preservation and patient survival.
• Always correlate ECG findings with patient symptoms (chest pain, diaphoresis, dyspnea) and cardiac biomarkers.

Conclusion

Interpreting ECG in acute myocardial infarction requires understanding various patterns of ST-segment changes, T-wave abnormalities, and pathologic Q waves. Quick recognition of these findings enables prompt treatment, improving patient outcomes.

Source recommendations

1. American Heart Association (AHA) Guidelines for the Management of ST-Elevation Myocardial Infarction

1. https://professional.heart.org/en/science-news/2021-acc-aha-scai-guideline-for-coronary-artery-revascularization
2. https://www.ahajournals.org/doi/10.1161/cir.0b013e3182742cf6
3. https://pubmed.ncbi.nlm.nih.gov/23256914/
4. https://www.ahajournals.org/doi/10.1161/01.cir.0000134791.68010.fa
5. https://pubmed.ncbi.nlm.nih.gov/23247304/

2. European Society of Cardiology (ESC) Guidelines for Acute Coronary Syndromes

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-Coronary-Syndromes-ACS-Guidelines
2. https://academic.oup.com/eurheartj/article/44/38/3720/7243210
3. https://pubmed.ncbi.nlm.nih.gov/37622654/
4. https://academic.oup.com/eurheartj/article/42/14/1289/5898842
5. https://pubmed.ncbi.nlm.nih.gov/32860058/