A filter to suppress ECG baseline wander and preserve ST-segment accuracy in a real-time environment

Accurate monitoring of the ST-segment displacements in real-time environments can be distorted by the nonlinear phase response of a baseline filter such as the single-pole, high-pass (0.5 Hz) filter that is standard in the industry today. The authors have previously constructed a four-pole null phase (1.0 Hz) filter that is nearly ideal in suppressing baseline wander while preserving ST-segment accuracy; however, this foreward/backward filter requires capture of a large ECG segment before filtering, thereby producing a delay that is unacceptable in a real-time environment. As a practical compromise, a two-pole, phase-compensated (1.0 Hz) filter was constructed while introducing a small time delay (160 ms). It performs much better than the "standard filter" and almost as well as the "ideal" filter in several tests, namely (1) suppression of baseline wander in a series of ECGs, (2) suppression of artificial baseline, (3) response to a triangular impulse wave (American Heart Association test), and (4) J-point displacement in several ECGs.