Abstract 15586: Optimum Heart Rate Response to Autonomic Regulation Therapy is Frequency Dependent
Background: Cervical vagus nerve stimulation (VNS) elicits beneficial central and peripheral cardiovascular effects; such responses being sub-served by activation of ascending afferent and descending efferent projections. However, optimal VNS parameters required to elicit beneficial neuronal stabilizing effects on regional cardiac function have not been determined.
Methods: Normal canines (n=4) were implanted with VNS devices on the right cervical vagus nerve and programed to deliver chronic, intermittent stimulation (14 s ON, 66 s OFF). Holter monitors recorded ECG continuously for 24 hours during various combinations of stimulation frequency (5, 10, and 20 Hz) and pulse widths (250 and 500 μs). VNS amplitude (mA) was programmed to the cardiac response threshold (a 10% acute decrease in heart rate during VNS); it averaged 1.75 mAmp.
Results: Chronic right-sided VNS elicited a modest reduction in heart rate and an increase in heart rate variability at 5 and 10 Hz, but not 20 Hz. The magnitude of the cardiac response was dependent on the stimulation amplitude, frequency, and pulse width. With a 1.75 mAmp stimulation amplitude, the maximum cardiac response occurred at a stimulation frequency of 10 Hz (p<0.025), with a larger effect at pulse duration of 500 μs compared to 250 μs (p<0.025). 20 Hz VNS reverted the evoked heart rate response to levels equivalent to baseline.
Conclusion: Chronic autonomic regulation therapy at the cardiac response threshold elicits changes in mean heart rate and heart rate variability (24 hour epoch) that are dependent on pulse duration and frequency. The cardiac stabilizing effects of lower frequency stimulation are mitigated at higher VNS frequencies, likely reflective of progressive engagement within multiple levels of the cardiac neuraxis with increasing stimulus density. Lower level VNS engenders effective cardiac control with minimal adverse effects.
- © 2013 by American Heart Association, Inc.