American Board of Internal Medicine (ABIM) Certification Practice Exam

Right axis deviation and incomplete right bundle branch block may indicate which condition?

1. Atrial septal defect

2. Mitral valve stenosis

3. Aortic stenosis

4. Heart failure

The correct answer is: Atrial septal defect

Right axis deviation and incomplete right bundle branch block are findings on an electrocardiogram (ECG) that can be associated with various cardiac conditions, particularly those that affect the right side of the heart. Atrial septal defect (ASD) is a congenital heart defect that results in a shunt between the left and right atria. This condition leads to increased blood flow to the right atrium and right ventricle, causing volume overload. Over time, this can lead to structural and electrical changes in the right heart, which may manifest as right axis deviation and incomplete right bundle branch block on the ECG. The mechanism here involves the right heart's response to chronic volume overload. The right ventricle may become hypertrophied as it faces an increased workload due to the extra blood from the left atrium. This hypertrophy, along with the altered conduction pathways due to the structural changes, results in the specific ECG findings noted. Other options, while they may cause various symptoms and changes in the heart, do not typically lead to the same electrical alterations seen in ASD. For example, mitral valve stenosis primarily affects the left heart and may lead to right heart changes, but the specific combination of right axis deviation and incomplete right