High gain, high frequency atrial vectorcardiograms in normal subjects and in patients with atrial enlargement

Atrial forces in three planes of the timed vectorcardiogram were analyzed for magnitude and direction in 100 normal subjects and 304 patients with proved heart disease. In the horizontal plane, a value of the initial half of the P loop or right atrial component of 0.06 mv. anteriorly for an adult (or 0.08 mv. for a child) included all normal subjects for two standard deviations. Values in excess of these figures —that is, anterior displacement of 0.07 mv. (0.09 mv. for a child) or greater—were consistent with right atrial enlargement. In the horizontal plane, a left atrial vector of 0.045 mv. or less included 96 per cent of the normal subjects, both children and adults; hence, posterior displacement of more than 0.05 mv. of the late portion of the P loop was evidence of left atrial enlargement. A leftward displacement of this component of 0.10 mv. or more in adults (0.14 mv. in children) also exceeded normal limits and was taken as evidence of left atrial enlargement. The timed vectorcardiogram employing the criteria presented was over three times as sensitive in detecting atrial abnormality in the abnormal subjects as the electrocardiogram employing conventional criteria. Better visualization of P wave activity in the conventional electrocardiogram was afforded by increasing the gain 5 to 10 times the normal level. Because right and left atrial enlargement is an important factor in the diagnosis of congenital and acquired heart disease, a more graphic representation of these electrical forces is of great practical value.