Electrocardiogram filter

The invention presents techniques for identifying signals detected by electrodes on the body of a patient as part of a reading of the patient's electrocardiogram. A signal processor digitally filters the signal from the body, resulting in an electrocardiogram signal and a signal that identifies the presence and timing of signals from a pacemaker in the body. Other signals, such as a signal that reflects the quality of the electrical connection of the electrode to the body, may also be obtained by digital filtering.