Comparison of indirect and direct sinuatrial conduction time by synchronous sinus node electrogram.

In order to determine whether or not the estimated indirect sinuatrial conduction time represented the real sinuatrial conduction time, we recorded the synchronous sinus node electrogram, on which direct sinuatrial conduction time could be measured during constant atrial pacing, in 21 cases with normal sinus node function. The results show first that the difference between direct and indirect sinuatrial conduction time is statistically significant (P less than 0.05); the correlation of the two is poor (r = 0.29). Second, the direct sinuatrial conduction time after constant atrial pacing is significantly longer than that before constant atrial pacing, which means constant atrial pacing has resulted in obvious depression of conduction through the sinus node. Our conclusion is that estimated indirect sinuatrial conduction time does not represent real sinuatrial conduction time. The calculation formula using constant atrial pacing has been based on a major unproven assumption.