Different determination of sinoatrial conduction time (SACT) in man

Using intracardiac recordings of electrical activity and programmed electrical right atrial stimulation of the human heart, the sinoatrial conduction time (SACT) in the method of Strauss et al. 1973 (SACTc) was calculated in 80 patients with and without disturbances of rhythm and compared to the modified measurement of the SACT in the method reported by Narula et al. in 1978 (SACTN). The number of continuously stimuli varied from 4, 8 and 16 stimuli with a frequency of 10% just above the averaged spontaneous frequency. The best correlation was found between the SACTc and the SACTN16 (r = 0.74; p less than 0.001) with a regression line of: SACTN16 = 1.04 SACTc + 28.6. Under these conditions, as opposed to SACTN4 or SACTN8, the most favourable reproducibility and relative coefficient of variation (rVk) could be observed: SACTN16: rVk = 9.5%; r = 0.91; SACTN8: rVK = 12.3%; r = 0.89; SACTN4: rvK = 24.3%; r = 0.53. Higher individual values for SACTN16 were found by continuous atrial stimulation as compared to other methods of determination indicating mainly a higher depression of sinus node automaticity due to overdrive suppression. Under parasympathicolysis (1 mg atropine) the lowest values of SACT were found for SACTN4 (45.9 +/- 20.7 ms) coming closest the "true" SACT, since these conditions neither an increase of the refractory period nor an overdrive suppression exert an influence.