[Superior axial deviation in the young adult. An electro-vectorcardiographic study]

We analyzed the VCGs of 100 young subjects without apparent cardiac disease showing an ECG superior Axis Deviation, i.e. AQRS greater than - 30 degrees, and a rS aspect in V1. Our findings demonstrated that, in these subjects, the superior axis deviation is due to a distal right bundle branch block with posterior displacement of the terminal forces in 78% of the cases. The other cases being left anterior hemiblocks, either isolated (12%) or associated with a block of the anterior subdivision of the right bundle branch (10%). The differential diagnosis, easy on VCG, is sometimes very difficult on ECG. The most reliable ECG criteria to discriminate this kind of right bundle branch block from left anterior hemiblock are: intrinsic deflection in a VL-V6 greater than or equal to 0.015" (sensitivity 100%; specificity 57%), RV6/Ra VL ratio greater than 1 (sensibility 100%; specificity 50%) and the presence of a notched R wave in L2, L3 and a VF (sensitivity 90%; specificity 100%).