Measurement of the sinoatrial conduction time using direct recording of sinus node electrogram. Preliminary study in...

Sinus node electrogram is characterized by a smooth, low-frequency upstroke slope beginning before P wave and followed by a rapid deflection that results from initial atrial activity. Sinoatrial conduction time (SACT) can be measured directly (SACTD) from the sinus node electrogram as the interval from the onset of the upstroke slope to the onset of atrial activation. In our laboratory the values found in 20 patients with normal sinus node function ranged between 50 and 130 msec (mean 86.5 +/- 21.3). We compared SACTDs with those obtained by three indirect methods using the atrial premature stimulation technique (Strauss method) or the asynchronous pacing (Narula/Raviele method). In this part of the study were included 15 patients presenting A3A4 = A1A1 (i.e. without a depression of the sinus node) in the zone of reset and A2A3 greater than A1A1 (i.e. positive SACTs) when Narula/Raviele method was employed. No correlation was observed between directly measured and indirectly estimated SACTs. On this last point opposite conclusions have been drawn by the few papers published until now. The discrepancy may be explained by the different incidence on the study populations a) of the various factors determining the return cycle length b) of the measurement errors in SACTD.