Is accurate recording of the ECG surface Laplacian feasible?

Experimental and model studies mere performed to measure the electrocardiog raphic surface Laplacian using a rectangular finite difference approximatio n. The experimental approach used ten normal subjects with two sites on the torso. Electrode spacing was 2 cm. The surface Laplacian is theoretically independent of rotation of the electrode array. The data showed considerabl e variation with rotation. Model studies employed a realistic U-dipole sour ce. A spherical volume conductor showed invariance with rotation, as antici pated theoretically, A realistic torso, however, showed variation with rota tion, although not as severe as that measured. A separate experimental stud y considered the signal-to-noise ratio (SNR) for the surface Laplacian, The average SNR was 3.3 and 2.5 at the two sites. These results raise serious questions about the practical ability to measure the surface Laplacian on t he torso.