Time-varying filtering for removal of baseline wander in exercise ECGs

Time-varying filtering techniques were applied to the problem of baseline correction by letting the cut-off frequency of a linear filter be controlled by the low-frequency properties of the electrocardiogram signal. The time-varying filter was implemented as a bank of linear lowpass filters, in which each filter has a slightly differing cut-off frequency. All filters have a linear phase response. Sampling rate decimation and interpolation were used for efficient implementation of the filter. The performance of the technique was studied on ECG signals with different types of simulated baseline wander. The results are compared to the performance of linear, time-invariant filtering and to that of cubic spline interpolation. The results show that a substantial improvement in performance can be achieved when using time-varying filtering, especially at low heart rates or during episodes with excessive baseline wander