We have previously shown that in healthy young men autonomic control of the sinoatrial (SA) and AV node may be independent during sleep. It is conceivable, that this independence is lost in patients with high sympathetic activity. This would be in analogy to exercise in normal subjects, where an increase in sinus rate is associated with a shortening of the PR interval. 2. The aim of this study was to investigate whether this independence of SA and AV nodal autonomic modulation is maintained in patients with congestive heart failure. 3. For analysis of heart rate variability (HRV) the ECG was online digitized from 10 pm to 6 am in six patients with congestive heart failure (EF < 40%). The onset of P-waves and QRS-complexes was recognized by a computer algorithm with an accuracy of +/-1 ms. Power spectra of PR intervals and PP intervals were calculated for consecutive 256 second segments. The power in the high frequency component. (HF, 0.15 - 0.4 Hz) of PP intervals was used as an index of vagal drive to the SA node. The vagal input to the AV node was determined by the spectral power of the corresponding PR intervals. 4. All patients showed the typical spectral peak in the HF band, both in PP and PR. The power spectral density of HF varied over time with different patterns for PP and PR. The ratio of the HF power derived from PP and PR was calculated for each segment. This ratio was not constant, but showed a distinct time course. 5. Congestive heart failure did not abolish the independence of vagal modulation of SA and AV node, as assessed by the HF power derived from PP and PR intervals. Thus, the difference in vagal traffic to the SA and AV node was maintained even in the setting of high background sympathetic activity. Further investigation is needed to analyze potential factors responsible for this difference in patterns and the clinical relevance of this finding.
