A standardized procedure for locating and documenting ECG chest electrode positions: consideration of the effect of breast tissue on ECG amplitudes in women.

Continuing uncertainty exists about standardized procedures for the placement of electrocardiographic (ECG) chest electrodes, technical variability being the largest error source for short-term variations in amplitudes and waveforms of the chest lead ECGs. To avoid presumed attenuation of ECG amplitudes by abundant breast tissue, anterolateral chest electrodes in women are often placed under the breasts and too low. There is also considerable uncertainty about locating the midclavicular line and the V4 electrode, particularly in obese persons and in women. We examined the effect of breast tissue protuberance on ECG amplitudes using ECG and anthropometric data on 6,814 women included in the Atherosclerosis Research in Communities Study (ARIC). The R wave amplitudes in anterolateral chest leads and the Sokolow-Lyon voltage decreased (P < .001 for all), and RaVL and the Cornell voltage increased significantly with increasing breast protuberance (P < .001 for all). However, these effects were small (15 microV or less for each 1-cm increment in breast protuberance), and R2 values were less than .01, indicating that breast protuberance alone explained less than 1% of ECG amplitude variations. When chest size and breast protuberance estimates were entered simultaneously into a multivariate regression model, chest size appeared to dominate, and model R2 values increased for positive associations with RaVL (R2 = .12) and the Cornell voltage (R2 = .04). Combined model R2 values remained < or =.01 for all other ECG amplitudes. A detailed step-by-step standardized electrode placement procedure was formulated. Because of the difficulties encountered in locating the left midclavicular line by visual inspection, we introduced well-defined procedures for identification and documentation of lateral chest electrode placement locations as a quality control method for clinical trials. Population data from the Third National Health and Nutrition Survey on the distributions by sex and race of chest electrode V4 and V6 locations and anthropometric data on chest size and shape are presented in order to facilitate evaluation of the comparability of electrode placement procedures in various studies and for quality control in clinical trials. It is concluded that standardized procedures to document chest electrode placement locations are feasible. Breast tissue appears to have a practically negligible effect on ECG amplitudes, and in women, the placement of chest electrodes on the breast rather than under the breast is recommended in order to facilitate the precision of electrode placement at the correct horizontal level and at the correct lateral positions.