A new electrocardiographic concept: V1-V2-V3 are not only horizontal, but also frontal plane leads

According to conventional teaching, the limb leads in the electrocardiogram (ECG) represent the frontal plane electrical vectors of the heart, whereas the chest leads signify the horizontal plane. The anterior chest leads V1-V2-V3, however, also have strong frontal plane representation which can result in morphological similarities in these leads to the augmented unipolar leads of the Einthoven triangle. This review highlights the significance of recognizing V1-V2-V3 as not only horizontal, but also as frontal plane leads. Appreciation of this phenomenon helps elucidate a colorful variety of clinically important but seemingly bizarre ECG manifestations that could not be explained otherwise.