Which electrocardiogram (ECG) leads show ST elevation in a septal infarction?

ST Elevation in Septal Infarction: ECG Lead Patterns

In septal infarction, ST elevation is typically seen in leads V1-V4, with V1 showing elevation when the proximal left anterior descending coronary artery is occluded above the first septal branch. 1

Anatomical Correlation of Septal Infarction

Septal infarction occurs due to occlusion of the left anterior descending (LAD) coronary artery, which supplies the interventricular septum. The specific ECG findings depend on the location of the occlusion within the LAD:

Proximal LAD Occlusion (Above First Septal Branch)

• ST elevation in leads V1-V4
• ST elevation in leads I and aVL
• Often ST elevation in aVR
• Reciprocal ST depression in leads II, III, aVF, and sometimes V5 1

Mid-LAD Occlusion (Between First Septal and First Diagonal)

• No ST elevation in lead V1 (basal septum spared)
• ST elevation in aVL
• ST depression in lead III 1

Distal LAD Occlusion (Below First Septal and First Diagonal)

• No ST elevation in V1, aVR, or aVL
• No ST depression in leads II, III, or aVF
• ST elevation more prominent in V3-V6 and less prominent in V2 1

Diagnostic Criteria for ST Elevation

The American College of Cardiology and American Heart Association recommend the following thresholds for ST elevation:

• V1-V3: ≥1 mm (0.1 mV)
• V2-V3: ≥2 mm (0.2 mV) in men, ≥1.5 mm (0.15 mV) in women 2

Clinical Pearls and Pitfalls

Important Considerations:

1. Pseudo-septal infarction: Be aware that cranially misplaced precordial leads V1 and V2 can falsely suggest septal infarction. Check P wave morphology in lead V2 to help identify this technical error. 3

2. Anteroapical vs. Anteroseptal: Recent research using cardiac MRI suggests that what has traditionally been called "anteroseptal" infarction (with ST elevation in V1-V4) actually represents predominantly apical territory involvement rather than basal anteroseptal involvement. 4

3. Right Ventricular Infarction: Isolated ST elevation in leads V1 and V2 can sometimes represent right ventricular infarction due to occlusion of the right ventricular marginal branch of the right coronary artery, rather than septal infarction. 5

4. Distinguishing Acute MI from LV Aneurysm: When differentiating acute septal infarction from left ventricular aneurysm, examine the T-wave to QRS amplitude ratio. If any lead from V1-V4 has a T-wave amplitude to QRS amplitude ratio ≥0.36, acute MI is more likely. 6

Summary of ECG Leads Showing ST Elevation in Septal Infarction

• Primary leads: V1-V4 (with V1 elevation specifically indicating proximal LAD occlusion involving the basal septum)
• Additional leads with proximal LAD occlusion: I, aVL, sometimes aVR
• Reciprocal changes: ST depression in II, III, aVF (with proximal occlusion)

Remember that the pattern of ST elevation helps localize the site of occlusion within the LAD, which has important implications for prognosis and management.