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 at 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 V1 to 0.98 inches at lead V4. Overall, 64% of precordial electrodes were placed within a radius of 1.25 inch, ranging from 56% for lead V6 to 74% for lead V4, 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 V1 and V2, indicating that these electrodes are commonly placed both high and wide of their anatomically defined precordial sites. Similarly, there was an inferior and left-ward displacement of more than 0.625 inch in 30-50% leads of routine applications of V4 through V6, indicating that these lateral precordial electrodes are commonly placed both low and wide of their respective anatomic sites.