Which change in QRS complex indicates left axis deviation (LAD)?

Which change in QRS complex indicates left axis deviation (LAD)?

• A. Positive in lead AVF and negative in lead I
• B. Positive in lead I and negative in lead AVF
• C. Negative in both leads
• D. Positive in both leads

Answer: (B)

The correct answer indicates that left axis deviation (LAD) corresponds to a positive QRS complex in lead I and a negative QRS complex in lead AVF. In this context, lead I is oriented to detect electrical activity that moves laterally (from right to left), while lead AVF assesses activity directed towards the feet.

When the QRS complex is positive in lead I, this suggests that the heart's electrical activity is primarily moving towards the left side of the body. Conversely, a negative QRS complex in lead AVF indicates that there is little to no electrical activity directed downwards, suggesting a shift in the electrical vector that’s more oriented upwards and towards the left. Together, these patterns are characteristic of left axis deviation.

This knowledge is crucial in interpreting EKGs, as it helps in identifying potential underlying cardiac conditions. Understanding the relationship between the QRS complex in these leads and the axis of the heart is fundamental in the analysis of cardiac function.