Beat-to-beat detection of His-Purkinje system signals using adaptive filters

Noninvasive techniques to record the activation wave from the His-Purkinje system have so far depended largely on signal averaging. Although this approach produces representative signals, any beat-to-beat variations are removed by the averaging process. These beat-to-beat variations are important in the diagnosis of many heart abnormalities, particularly arrhythmias. The paper describes an experimental system which can detect His-Purkinje system electrograms at the body surface while preserving beat-to-beat variations. The system uses a number of different techniques, but an important feature is the use of an adaptive filter to reduce additive noise. The experimental system is not real-time, as the adaptive filtering is performed offine using software, but a real-time hardware implementation is quite feasible. The system's ability to detect beat-to-beat variations has produced a number of interesting results, which are discussed. These include a cyclic variation in a normal subject, believed to be due to the modulating effects of breathing, and signals from a patient suffering from second degree A-V block.