Differences in QRS axis measurements, classification of inferior myocardial infarction, and noise tolerance for 12-lead electrocardiograms acquired from monitoring electrode positions compared to standard locations.

We tested whether the "Lund" (LU) electrode-placement system compared to the Mason-Likar (M-L) electrode-placement system would produce waveforms more similar to those of standard electrocardiograms (ECGs) with regard to the QRS axis in the frontal plane and QRS changes of inferior myocardial infarction (MI). We also tested whether LU was more noise immune than standard, and whether the noise immunities of the LU and M-L systems were comparable. Four 12-lead ECGs were recorded in 80 patients-2 standard ECGs, 1 LU ECG, and 1 M-L ECG. Further, 6 ECGs were recorded for 11 patients and 9 healthy volunteers-2 standard, 2 LU, and 2 M-L ECGs-while the subjects performed limb movements. Three electrocardiographic readers made blinded assessments of noise levels. QRS scores in patients with inferior MI differed significantly between standard and M-L ECGs but not between standard and LU ECGs. Few of those without QRS changes of MI received QRS scores, but not more often on LU ECGs than on standard ECGs, and never on M-L ECGs. QRS axis differences were small between standard and LU ECGs, but large between standard and M-L ECGs. The LU system was significantly more noise immune than the standard, whereas the difference in noise immunity between the M-L and LU systems was not significant. In conclusion, the results indicate that LU might constitute a uniform convention for "diagnostic" ECGs and for monitoring electrocardiographic applications.