An electrocardiogram (ECG) in a patient with a systolic ejection murmur that shows an incomplete bundle branch block in the precordial lead is most consistent with:

Many patients with secundum ASDs have an incomplete bundle branch block on their ECG. This is in contradistinction to patients with ostium primum defects, who often have a left axis detion. Although the ECG is not pathognomonic of the defect, the findings are sometimes helpful along with other clinical and diagnostic information toward elucidating the nature of the defect.