[Does the sinoatrial node conduction time depend on heart rate?]

The informations about the dependence of sinoatrial conduction time (SACT) on heart rate (HR) are unequivocal. The aim of the study was to establish if such a dependence really exists. The study group comprised 24 patients (9 women and 15 men) aged 42-71 years, mean 55.8. All the patients presented atrial premature contractions of various etiology. No agents affecting heart electrophysiology were administered until the study was completed. In every patient SACT was estimated by means of the Strauss formula from the 24-hr ecg and from transoesophageal single impulse stimulation. SACT obtained from 24-hr ecg was 156.2 +/- 33.1 ms; whereas the one respectively, calculated from the transoesophageal stimulation was 119.0 +/- 21.0 ms. Despite a significant difference between the results (p less than 0.001), the SACT values obtained with both methods correlated well with each other (r = 0.712; p less than 0.01). The dependence of SACT on basic heart cycle length was observed in 9 pts during 24-h ecg (37.5%). Among these pts SACT was shortened with higher and lengthened with lower HR. In the remaining 15 pts this dependence didn't occur, neither it occurred in any patients examined with the single impulse stimulation. The results suggest that the dependence of SACT on HR is not a constant phenomenon and that it occurs only in a part of the examined population.