If the QRS is positive in lead I and negative in lead AVF, what condition does this indicate?

If the QRS is positive in lead I and negative in lead AVF, what condition does this indicate?

• A. Normal axis
• B. Left axis deviation (LAD)
• C. Right axis deviation (RAD)
• D. Incomplete right bundle branch block

Answer: (B)

When the QRS complex is positive in lead I and negative in lead aVF, this indicates left axis deviation (LAD).

In a normal heart, the electrical activity generally moves down and to the left, which is represented by a positive QRS in both lead I and lead aVF. When a QRS is positive in lead I, it suggests that the electrical activity is directed towards the left side of the heart. Conversely, a negative QRS in lead aVF indicates that the electrical activity is directed upward, away from the inferior portion of the heart. This upward direction combined with the leftward direction signifies that the overall axis of depolarization is deviated towards the left, which is characteristic of LAD.

LAD can be associated with conditions such as hypertension, left ventricular hypertrophy, or a previous antero-septal myocardial infarction. Understanding the axis orientation is crucial for identifying underlying cardiac conditions, and in this case, the combination of the QRS findings directly points to left axis deviation.