Methods for recording electrograms of the sinoatrial node during cardiac surgery in man

Recent reports have shown that it is possible to record extracellular electrograms from the rabbit and dog sinoatrial (SA) node. We applied similar techniques to record SA nodal activity in 23 patients who underwent cardiac surgery for various forms of heart disease. Both a bipolar technique, using pairs of electrodes at various interelectrode distances, and a unipolar technique, using an exploring and an indifferent electrode, were used. To record SA nodal electrograms, polarity was reversed from the conventional electrocardiographic recording; high amplification (100 microV/cm) and low-pass filters (0.15-20 Hz) were used. SA nodal electrograms were recorded from eight of 12 patients using the bipolar method and from nine of 11 patients using the unipolar method. There were no significant differences in the success rate or quality of the recording between the two methods. However, the unipolar method allowed a more accurate localization of the SA node. Human SA nodal electrograms resembled those of the dog and rabbit and showed two distinct slopes: a diastolic slope and an upstroke slope preceding the P wave of the ECG, SA conduction times were 32.4 +/- 2.8 msec (mean +/- SEM) at sinus (PP) cycle lengths of 587.6 +/- 35.6 msec for the bipolar method, and 38.2 +/- 3.2 msec at sinus (PP) cycle lengths of 712.2 +/- 50.7 msec for the unipolar method. These methods for recording of extracellular SA nodal electrograms in man may prove useful in 1) localization of the SA node during open heart surgery and 2) assessment of SA nodal function in health and disease.