Effects of limb electrode placement on the 12- and 16-lead electrocardiogram

The effects of three common limb electrode placement configurations on ECG signal morphology were examined, including the standard electrode placement of the electrodes on the extremities, the Mason-Likar placement, and the Lund placement. A non-traditional asymmetric configuration of placing the LA electrode on the upper arm with the RA electrode on the torso (below the clavicle) was also investigated. A series of 16-lead ECGs were acquired from 150 subjects representing a broad range of diseases. Effects of the limb electrode placement on axis measurements, QRS amplitudes, ST levels, and infarctions were studied. On average, the P, QRS, and T axes all exhibited rightward shifts as the electrodes were moved away from the extremities, but more generally, the axis became more vertical, with the largest shifts occurring when the standard ECG axis measurement was close to 0 degrees and tending to exhibit leftward shifts for ECGs with a standard axis measurement between 0 and -90 degrees. Voltage changes were consistent with axis shifts in the frontal plane (decreased lateral and increased inferior lead voltages), with the largest mean change a reduction in R wave amplitude of lead I going from the standard to the Mason-Likar configuration. In the precordial leads, Q and/or S magnitudes decreased in right-sided leads (V4r, V1, V2, V3) and R magnitudes increased in lateral leads (V3-V9) as the arm electrodes moved toward the trunk, suggesting a posterior shift in the mean QRS axis. ST deviations in the lateral and posterior precordial leads tended to be mimicked in lead III when the electrodes were moved from the extremities to the torso. Over half (13 of 25) of the ECGs exhibiting criteria for inferior infarct in the standard configuration had that criteria erased when the electrodes were moved to the Mason-Likar positions. The largest single effect on the ECG resulted from moving the LA electrode from the shoulder to the clavicle. The asymmetric configuration with the RA electrode on the torso and the LA electrode on the upper arm may offer some compromise between noise and faithfulness to the standard configuration in noisy environments such as exercise testing or monitoring.