A method and apparatus for processing electrocardiographic signals of a patient. The apparatus comprises ten or fewer electrodes connected to a patient at least one of the standard twelve lead ECG electrode positions. The apparatus further comprises a plurality of ECG interpretation algorithms, each of the algorithms specifically tailored for analyzing a twelve lead ECG comprising both measured and derived ECG leads. The method of the present invention comprises determining whether an ECG lead is measured or derived and selecting an ECG interpretation algorithm based upon this determination.