Single vs. dual mode stimulation in spinal cord stimulation - what is the difference?

Objectives. Stimulation with dual percutaneous leads is often used in SCS. Either a single generator gives pulses to both leads simultaneously (single mode), or two generators give pulses to each lead alternately (dual mode) [1]. The aim was to compare theoretically the performance of these stimulation modes in terms of their ability to recruit the dorsal columns (DCs) and to evoke paresthesias. Methods. Computer simulations [2] of dual and single mode SCS with two leads having a 8 mm center-to-center contact spacing were performed. The leads were in parallel at distances of 1, 2, 3, and 4 mm (edge-to-edge) and symmetrical to the spinal cord midline. Stimulation with aligned guarded cathode (+ - +) combinations on both leads was simulated. The DC area recruited at discomfort threshold (DT, [3]) and its distribution among the left and right DC was calculated [4]. Results. As the distance between the leads was increased the recruited area declines from 2 to 0.9 mm2 in dual mode and from 3.65 to 2.8 mm2 in single mode. In single mode equal portions of both DCs are simultaneously recruited. In dual mode DC fibers are recruited mainly on the side corresponding to the active lead and changes to the opposite side as the stimulation switches to the other lead. Conclusions. Assuming that DC recruitment is linearly related to paresthesia coverage, modeling predicts that the overall paresthesia coverage in dual mode is less than in single mode. This effect is due to a lack of superposition of the electrical fields induced by the two leads, because pulses are applied alternately to each lead. In single mode, recruitment of the median DCs is improved, most likely resulting in a more intense paresthesia sensation in lumbosacral dermatomes. When in dual mode stimulation there is some overlap of the DC areas recruited with each lead separately, the double pulse rate in the area of overlap is likely to result in a more intense paresthesia sensation in the corresponding dermatomes. References 1. Devulder J, De Laat M and Rolly G. Dual channel electrostimulation in pain. Acta neurol. belg. 1998;98:195-198. 2. Holsheimer J. Computer modelling of spinal cord stimulation and its contribution to therapeutic efficacy (Review). Spinal Cord 1998;36:531-540. 3. He J, Barolat G, Ketcik B. Stimulation usage range for chronic pain management. Analgesia 1995;1:75-80. 4. Manola L, Holsheimer J, and Veltink PH. Technical performance of percutaneous leads for spinal cord stimulation: a modeling study. Neuromodulation 2005;8:88-99.