What EKG finding is indicative of a left anterior fascicular block?

A left anterior fascicular block is characterized by a specific pattern in the electrical conduction system of the heart. The most distinctive EKG finding associated with this condition is left axis deviation. This occurs due to the impairment of electrical impulses through the anterior fascicle of the left bundle branch, causing the overall depolarization vector to shift to the left.

In a normal EKG, the axis of the heart's electrical activity generally falls between -30° and +90°. However, when there is a left anterior fascicular block, the axis is typically shifted to the left beyond -30°, resulting in a left axis deviation. The absence of a right bundle branch block further supports this finding, making it a clear indicator of the fascicular block.

The other choices do not relate to the characteristic findings of a left anterior fascicular block. For instance, right axis deviation indicates a different type of conduction issue and is not consistent with a left anterior fascicular block, while a prolonged QT interval and ST segment elevation relate more to repolarization abnormalities and potential ischemia, rather than to fascicular block patterns.