Atrial and ventricular refractoriness in paced patients - Circadian variation and its relationship to autonomic nervous system activity

Aims To examine whether atrial and ventricular effective refractory periods exhibit circadian variation and whether the latter is correlated with fluc tuations in autonomic nervous system tone. Methods and Results We studied 24 patients aged 67(.)1 +/- 9(.)6 years. 11 of whom were paced for complete heart block and 13 for sick sinus syndrome. Atrial and ventricular effective refractory periods were measured bihourly over a 24-h period, using the pacemaker programming capabilities. at basic cycle lengths or 600 ms and 500 ms. During the same time period we evaluat ed autonomic nervous system activity in patients paced for complete heart b lock, expressed by spectral power indexes in low frequency and high frequen cy areas of heart rate variability. Atrial and ventricular effective refrac tory periods showed significant circadian variation at both basic cycle len gths, with the highest values occurring between 22:00 and 06:00. At times, the atrial and ventricular effective refractory periods of the patients wit h sick sinus syndrome differed significantly from those with complete heart block. Furthermore, atrial and ventricular effective refractory periods in patients with complete heart block exhibited a strong negative correlation with the low frequency/high frequency ratio. Conclusion Our data show that atrial and ventricular effective refractory p eriods in DDD paced patients exhibit significant circadian variation that i s strongly correlated with variations in autonomic nervous system activity in patients with complete heart block. (C) 2001 The European Society of Car diology.