Electrical Interaction between Implantable Vagus Nerve Stimulation Device and Implantable Cardiac Rhythm Management Device

Background: Autonomic regulation therapy via vagus nerve stimulation (VNS) was recently approved as a therapy for chronic heart failure, and will likely be utilized in patients who are also indicated for cardiac rhythm management device implantation. This study is designed to assess the degree to which VNS is likely to cause interference in the cardiac sensing of an implantable cardiac rhythm management device. Methods: A VNS stimulation lead and a cardiac sensing lead were placed in a simulated biological medium. A nonconductive carrier frame was used to position the leads at a precise electrode spacing. Stimulation was delivered through the VNS Therapy lead at a maximum output current and a variety of combinations of stimulation frequencies from 5-30 Hz and stimulation pulse widths from 130-1000 mu s. The electrode spacing began at 0 cm and was increased in 1 cm increments until the measured signal dropped below the cardiac rhythm management device noise floor for sensing. The test was conducted with both bipolar and unipolar sensing. Results: In the bipolar sensing configuration, the maximum sensed signal amplitude was 687 mu V at an electrode separation of 0 cm, signal frequency of 30 Hz, pulse width of 1000 mu s, and output current of 3.5 mA. In the unipolar sensing configuration, the maximum amplitude was 406 mu V. In both configurations, the measured signal with maximum stimulation intensity decreased significantly with electrode separation, and dropped below the noise floor at an electrode spacing of 3.0 cm. The sensed signal amplitude was further attenuated at lower stimulation amplitudes and pulse widths. Conclusion: Even at maximum neural stimulation intensity of 3.5 mA, at an electrode separation of at least 3.0 cm, neural stimulation did not result in a detectable level of interference with either bipolar or unipolar sensing. Because this separation is significantly smaller than the minimum electrode separation of 15 cm in clinical practice, VNS Therapy is not expected to interfere with the function of implantable cardiac devices.