Detection and continuous monitoring of intracardiac low-level potentials from the surface of the Langendorff-perfused heart.

By appropriate placement of two electrodes on the epicardiac surface of Langendorff-perfused hearts, His-bundle and preatrial signals can be recorded by the surface electrogram (S-ECG). These signals are difficult to detect because of their low amplitude of a few microvolts. To improve the monitoring of these low-level potentials we studied the His-bundle spike as detected by intracardiac electrodes and by epicardial records (S-ECG) and compared these signals in the time and frequency domain. The frequency spectra of these cardiograms were used to develop appropriate filters and high-gain amplifiers for a continuous monitoring of the His-bundle signal from the epicardiac surface. By means of such a monitoring system, high-frequency components of preatrial activities could be resolved also. The time coincidence of these spikes to the simultaneously recorded intraatrial electrogram from electrodes positioned near the sinus node and near the His-bundle is demonstrated. Hence, the early atrial signals likely yield information about sinoatrial conduction. Application examples of monitoring His-bundle signals and preatrial signals in a beat-to-beat manner are described also for various conduction blocks or arrhythmias. With this monitor the evaluation of characteristic parameters of the conduction system of the heart like HV-, AH- and A'H-time, and likely, SACT can easily be performed for every heartbeat on a digital oscilloscope with low resolution or a two-channel chart recorder. Small and intact hearts can be used with this system to detect intracardiac low-level potentials during the heart beat.