Variability of precordial electrode placement during routine electrocardiography

Placement of precordial electrodes by 30 experienced technicians during routine electrocardiography was compared with anatomically ascertained sites marked by ink visible only under ultraviolet ''black light'' in three men and five women. The distance and direction from each marked site to the center of the applied electrode was measured to allow calculation of both the linear magnitude of difference (derived from the square root of the sum of the squares of rise and run) and also the direction of difference (in quadrants) between the anatomically established location and the electrode al each precordial site. The average difference from the applied electrodes to the corresponding marked sites was 1.14 inches, ranging from a mean of 1.31 inches at lead V-1 to 0.98 inches at lead V-4. Overall, 64% of precordial electrodes were placed within a radius of 1.25 inch, ranging from 56% for lead V-6 to 74% for lead V-4 and 27% of precordial electrodes were placed within a radius of 0.625 inch. There was superior quadrant displacement of more than 0.625 inch in more than 50% of routine applications of leads V-1 and V-2, indicating that these electrodes are commonly placed both high and wide of their anatomically defined precordial sites. Similarly, there was an inferior and leftward displacement of more than 0.625 inch in 30-50% leads of routine applications of V-4 through V-6, indicating that these lateral precordial electrodes are commonly placed both low and wide of their respective anatomic sites.