Geometrical factors affecting the interindividual variability of the ECG and the VCG

Various measures for quantifying the interindividual variability of the electrocardiogram and the vectorcardiogram in healthy subjects are presented. An analysis of factors that may cause this variability is performed, in particular of the geometrical factors of body size, heart size, heart position, and orientation. The results indicate that the variations in the magnitude of the electrocardiogram as observed through leads placed on the anterior thorax are dominated by the solid angle at which the outline of ventricular mass is seen from points on the thorax. Heart size and body size as such play only a secondary role. The limited spatial sampling of the anterior thorax directly overlaying the heart causes the mean values of all measures of amplitudes in women to be lower than in men. The vectorcardiogram magnitude was found to be much less dependent on overall geometry and heart position, and, hence, also to be less dependent on gender.