Nighttime Differential Autonomic Modulation of Sinus and Idioventricular Automaticity and of Atrioventricular Nodal Conduction

Abstract

Background:Potential differential effects of the autonomous nervous system on sinus node and protected idioventricular automaticity and on atrioventricular nodal conduction have not been assessed in the same patients. Methods:The sinus cycle lengths, parasystolic cycle lengths, uncorrected QT intervals, and PR intervals were measured in control epochs and epochs of transient spontaneous maximal nighttime heart rate accelerations occurring between 1 and 4 AM. Noncontiguous epochs were selected to avoid potential accommodation‐like, or memory effects that could occur at the moments of abrupt acceleration or decelerations of sinus rate. Results: The longest sinus cycle lengths coincided with the longest parasystolic cycle lengths and uncorrected QT intervals, whereas the shortest sinus cycle lengths coexisted with the shortest parasystolic cycle lengths and the shortest QT intervals. In contrast, the PR intervals did not show a uniform behavior during the episodes of transient heart rate accelerations since they could increase, decrease, or remain the same. Conclusion: The different behavior of cycle lengths and PR intervals during nighttime heart rate increases, suggests that the autonomic modulation of the sinus node, idioventricular focus, and the AV node can be independent from each other. A.N.E. 1999;4(4):385–390