[The possibility of the detection of His bundle potentials using thoracic surface electrodes (author's transl)]

Under certain conditions, it is possible to record His bundle potentials from thoracic surface electrodes. These potentials, which are extremely weak on the chest wall, must be extracted from the "background noise" using an averaging method. The required signal being situated before the R wave, and at a constant distance from the latter, the potentials collected from the thoracic electrodes are amplified, numerised and despatched to a memory which retains only the values preceeding the R wave and produces a summation of successive cycles, causing them to coincide using a synchronisation signal. This is achieved with the aid of a correlator. Amongst 66 patients studied, a signal which most likely corresponded to His bundle activity was obtained in 1/3 of cases. Correlation obtained in 7 cases by the use of invasive techniques indicated that the principal source of error was the "after potential" of the P wave when the PR interval is short. This was seen in one case, correlation in the other 6 being good. The method will require further work before being available for clinical use, where its primary indication would seem to be the study of long PR intervals.