Ganglionic mechanisms contribute to diminished vagal control in heart failure

Background-Previous work has shown that spontaneous and stimulated vagal activity is diminished in heart failure (HF) despite upregulation of functional postsynaptic cholinergic mechanisms, We therefore examined function of the postganglionic neuron in the paced canine model of HF as a possible site for diminished control. Methods and Results-We measured sinus cycle length changes in response to electrical stimulation of preganglionic and postganglionic parasympathetic neurons innervating the sinoatrial node in control and HF dogs (both, n=8), Cervical vagus stimulation (preganglionic) demonstrated attenuated responses in the HF group at all levels of stimulation (P<0.05). Stimulation of the right atrial fat pad, containing both postganglionic nerves and terminals of preganglionic neurons, showed no such difference between control and HF (200+/-25 versus 192+/-18 ms). To ensure that preganglionic input and different levels of baseline sympathetic activity did not contribute to the group difference, similar stimulations were done in the presence of ganglionic and beta-adrenergic blockade, Under these conditions, postganglionic stimulation showed smaller changes in sinus cycle length, but the HF group response remained significantly higher than in controls (76+/-10 versus 20+/-2 ms; P<0.01), indicating that the difference was independent of preganglionic input and sympathetic activity. Conclusions-A component of attenuated parasympathetic control in HF is located within the peripheral efferent limb. This defect is located within the parasympathetic ganglion. Future work should be focused on determining mechanisms of attenuated ganglionic transmission so that means targeted at restoring vagal activity can be developed.