Cardiac field effects on the EEG.

The electrical field of the heart propagates throughout the entire body and causes changes in the surface potentials on the scalp that are superimposed on brain electric signals. When heart cycle-related EEG averaging is performed, e.g. in order to measure heart cycle-related brain potentials, the effects of the cardiac electrical field result in a high-amplitude artifact in the surface potentials. The topographic and temporal distributions of the cardiac field artifact were measured in 9 normal subjects. In addition, the effects of head-turning on the field were investigated. The electrocardiac artifact is most prominent during the QRS complex and during the T wave of the heart cycle. In both cases it is distinctly asymmetrical in relation to the hemispheres. A comparison of the scalp potentials and a computed vector ECG showed the 3-dimensional nature of the artifact. Non-computational strategies for the handling of the ECG artifact are discussed. A proper separation of the effects of the cardiac electrical field from heart cycle-related brain potentials is a prerequisite for the study of heart cycle-coordinated brain potentials.