What are the ECG (electrocardiogram) findings in a septal myocardial infarction?

ECG Findings in Septal Myocardial Infarction

The classic ECG finding in septal myocardial infarction is the presence of Q waves in leads V1-V3, though recent evidence suggests this pattern more accurately represents anteroapical rather than isolated septal involvement.

Key ECG Findings in Septal MI

• Q waves or QS complexes in leads V1-V3 are the traditional electrocardiographic definition of septal myocardial infarction 1, 2
• These Q waves typically measure ≥0.03 seconds in duration and ≥0.1 mV in depth in at least two contiguous leads 1, 3
• ST-segment elevation may be present in the same leads (V1-V3) during the acute phase 3
• T-wave inversion may follow in these leads as the infarction evolves 3

Anatomical Considerations

• Despite the traditional ECG terminology, studies show that the pattern described as "septal MI" actually represents anteroapical infarction rather than isolated septal involvement 2, 4
• Research indicates that in patients with Q waves in leads V1-V3/V4:
  • The apex is always affected and is usually the most severely damaged region 2
  • The septum is often affected but typically less severely than the apex 2
  • The culprit lesion is most commonly in the mid-segment of the left anterior descending artery (LAD), often after the first septal branch 2

Diagnostic Challenges

• The term "anteroseptal MI" may be a misnomer, as echocardiographic and angiographic findings suggest these patients have predominantly apical infarctions 2, 4
• A more accurate term might be "anteroapical MI" for the ECG pattern showing Q waves in V1-V3/V4 2, 4
• The American Heart Association and American College of Cardiology still use the traditional terminology in their guidelines, though they acknowledge the limitations 1

Clinical Implications

• The presence of Q waves in V1-V3 indicates myocardial necrosis that has already occurred 1
• During acute presentation, ST-segment elevation in these leads would indicate ongoing ischemia requiring urgent reperfusion therapy 1, 3
• The extent of ST-segment elevation correlates with the amount of myocardium at risk and prognosis 3
• More profound ST-segment shift involving multiple leads/territories is associated with a greater degree of myocardial ischemia and worse outcomes 1

Additional Considerations

• Serial ECGs are essential as MI findings evolve over time 3
• Comparison with previous ECGs, when available, is crucial for accurate interpretation 1
• The ECG by itself is often insufficient to diagnose acute myocardial ischemia or infarction and should be combined with clinical presentation and cardiac biomarkers 1, 3
• In patients with bundle branch blocks, particularly LBBB, the diagnosis of septal MI becomes more challenging and may require additional diagnostic methods 1, 3

Pitfalls in Interpretation

• A QS complex in lead V1 can be normal and should not be automatically interpreted as evidence of septal infarction 1
• Small, non-pathological septal Q waves (≤0.03 sec and ≤25% of R-wave amplitude) may be present in leads I, aVL, aVF, and V4-V6 1
• Other conditions that may mimic septal infarction on ECG include pre-excitation, cardiomyopathies, cardiac amyloidosis, and myocarditis 1
• The absence of Q waves does not rule out a septal infarction, especially in the acute phase 3

Understanding these ECG patterns is essential for accurate diagnosis and appropriate management of patients with suspected septal myocardial infarction, though clinicians should be aware that the traditional terminology may not perfectly align with the actual anatomical involvement.