His bundle electrocardiography: A 'push-button' apparatus for noninvasive recording

The His-Purkinje system is a specialized conduction system that participates in the control of cardiac contraction. Electrical signals from this system are not obtained by conventional ECG recording.In accordance with volume conductor theory, the potential generated by the His bundle should be recorded by surface electrodes. However, these potentials are too small to be discernible in the presence of background noise. A simple solution is to use signal averaging as a method for improving the signal to noise ratio. The leading edge of the QRS complex can be used to trigger the signal averager circuit to sum, in a time-locked relationship, a series of ECG signals. However, His bundle activity occurs in real time before the QRS complex. To overcome this problem, some investigators have employed elaborate hardware to average the ECG signals in delayed or reversed time. These methods cannot be used in the usual medical setting as they involve costly equipment, such as digital computers and FM data recorders, elaborate programming, and highly trained operators. In this report, the authors describe a simple technique for processing the conventional ECG signal to increase its signal-to-noise ratio, and particularly to discern H waves produced by the His bundle.