Adaptive sampling of intracellular and extracellular cardiac potentials with the fan method

Uniform sampling rates of 5000 samples s−1 and 15000 samples s−1 or more are required to accurately represent intracellular and extracellular cardiac electrograms. These high rates are necessary because of short intervals where rapid deflections occur; thus uniform sampling results in far too many samples from slow phases when voltages change little between consecutive samples. Adaptive sampling with the fan algorithm selects samples with an irregular temporal spacing that specifies each waveform with the minimum number of samples required for a given maximum error or tolerance ε. This paper describes the performance of the fan as a function of tolerance on cardiac action potentials and electrograms simulated with the Beeler-Reuter model or measured directly from the heart, including examples showing signal quality, average sampling rate and intervals between samples. With low tolerances of ɛα = 100 μV (intracellular) or ɛα = 25 μV (extracellular), the average fan sampling rates were about 8000 samples s−1 for measured waveforms, and about 200 samples s−1 for simulated ones. With higher tolerances of ɛβ = 1 mV (intracellular) or ɛβ = 60 μV (extracellular) average fan sampling rates near 200 samples s−1 were found in all cases. The results suggest that good quality measurements of action potentials and electrograms can be obtained with remarkably low average sampling rates.