Effects of digital resolution on characterisation of cardiac late potentials

The effects of amplitude resolution in the signal-averaged ECG are studied in relation to the analysis of cardiac late potentials. The statistical properties of ECG signals from 22 patients after myocardial infarction were investigated in terms of amplitude distribution and noise level for the material. It was found that unbiased averaging could be achieved using a resolution greater than 10 microV. The noise levels of the bandpass-filtered individual X, Y and Z leads (range of 1-10 microV) and the vector magnitude were also investigated. Marked intra-lead differences in noise level were found, indicating that analysis based on individual leads is preferable. The effects of quantisation noise on the vector magnitude were negligible for amplitude resolutions below 5 microV. However, the additional noise contribution at 5 microV could be compensated by a moderate increase in acquisition time. The sensitivity to noise was considered when determining the endpoint of the filtered QRS complex using the vector magnitude.