Manifest orientation: the theoretical link between the anatomy of the heart and the clinical electrocardiogram

Einthoven related the apparent direction of the heart's electrical activity to the potential differences manifest in the limb leads and the axes of their orientation. From this beginning the linked concepts of heart vector and lead vector, equivalent dipole and lead field, complex heart source and complex volume conductor have continued the electrocardiographer's search for deeper insight into cardiac function from examination of the surface expression. However, this conceptual evolution has been uneven and has littered practical interpretation with diagnostic criteria that depend on assumptions of uneven validity. The good news is that some of the criteria are surprisingly helpful and that the shattering and reassembling of the conceptual framework relating the heart to the electrocardiogram may facilitate the construction of a more comprehensive and effective diagnostic approach.