Atrial and ventricular refractoriness in paced patients; circadian variation and its relationship to autonomic...

To examine whether atrial and ventricular effective refractory periods exhibit circadian variation and whether the latter is correlated with fluctuations in autonomic nervous system tone.

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 of 600 ms and 500 ms. During the same time period we evaluated autonomic nervous system activity in patients paced for complete heart block, expressed by spectral power indexes in low frequency and high frequency areas of heart rate variability. Atrial and ventricular effective refractory periods showed significant circadian variation at both basic cycle lengths, with the highest values occurring between 22:00 and 06:00. At times, the atrial and ventricular effective refractory periods of the patients with 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.

Our data show that atrial and ventricular effective refractory periods in DDD paced patients exhibit significant circadian variation that is strongly correlated with variations in autonomic nervous system activity in patients with complete heart block.