The part of AV-node variability in total heart rate variability evaluated by fixed rate atrial pacing

In thirteen patients with coronary artery bypass graft surgery, heart rate variability (HRV) was investigated shortly after arrival in an intensive care unit. Recordings were made under 3 different conditions: sinus rhythm (SR), and fixed rate atrial pacing with increases in heart rate of 25% (p1) and 50% (p2). When using a fixed rate atrial pacemaker there was still a determinable HRV discernible from noise. HRV decreased in both pacing conditions inversely to heart rate (p<0.05). Parasympathetic influence increased from SR to p1 (p<0.005) with no more increase to p2. The extent of the reduction of variability was comparable to the variability after cardiac transplantation. Local circuits, mechanical effects and the influence of the autonomic nervous system on the atrioventricular conduction may explain these findings.<>