An approach to direct detection of sinus nodal activity in man

We are reporting a series of 13 out of a total of 16 patients in whom sinus nodal activity was recorded with the use of intra-atrial electrodes, during diagnostic His-bundle electrocardiography investigations. The protocol consisted of the simultaneous monitoring of the following intra-atrial points: high right atrium, low lateral right atrium, left atrium and the His-bundle electrogram (HBE), which accompanied the detecting sonde placed as a loop in the superior vena cava, with the electrodes facing the sinus nodal area. This permitted an adequate assessment of the sequence of the depolarizing activity. All patients showed sinus nodal potentials preceding the initiation of the P-wave in the surface-EKG or the atrial potential in the high right atrial lead, respectively, in the range of 60 to 270 msec depending upon the functional status of the sinus node in each patient. Such waves were clearly separated from the initiation of the atrial potential by an isoelectric line and showed functional traits compatible with the S-A nodal functions, as many authors have previously reported in experimental animal models. The text contains a review of the relevant literature and discussion upon the diagnostic significance of this method in the assessment of sinus nodal disease.