Clarifying the Scientific Knowledge Pertaining to Burst Waveforms in Spinal Cord Stimulation

To the Editor: Drs. Dirk De Ridder and Sven Vanneste submitted a public commentary on our journal article “Conventional-SCS vs. BurstSCS and the Behavioral Effect on Mechanical Hypersensitivity in a Rat Model of Chronic Neuropathic Pain: Effect of Amplitude” (1). Here, we respond to their commentary. In the interest of full transparency, we note that Dr. De Ridder has filed patents related to burst stimulation, which are apparently now controlled by Abbott (2). The motivation of our original publication was to provide insights on the dosing effects of sub-perception burst and perception tonic stimulation. These stimulation waveforms have many parameters that can be explored and optimized, one such parameter being amplitude. Our research found that while both waveforms are equally effective, their optimal effects are achieved at different amplitude settings. A systematic set of research studies such as the one we presented (1) is a rigorous approach to advance the field. Therefore, it is important to note that public commentaries are not peer reviewed and thus may contain scientifically inaccurate statements as is the case here. One example is the apparent misinterpretation in the commentary from Drs. De Ridder and Vanneste that an excitatory postsynaptic potential (EPSP) is a “super action potential” in the Sherman reference they cited. The term “super action potential” does not appear in the Sherman article or other peer reviewed literature. In reality, an EPSP is a subthreshold response of a neuron that by itself may not generate an action potential. Drs. De Ridder and Vanneste criticized our study in part based on the different shape of the burst waveform we used (active charge recovery or “active recharge”) compared to the burst waveform developed by Dr. De Ridder (a particular version of passive charge recovery or “passive recharge”). However, whether active charge recovery and passive charge recovery burst spinal cord stimulation (SCS) act via different mechanisms remains an open question to be answered by future research, but the evidence to date indicates that both can alleviate pain. Preclinical studies using active charge recovery burst SCS (1) and passive charge recovery burst SCS (3) have shown that both are as effective as tonic SCS in reducing mechanical hypersensitivity. In addition to the fact that no single burst waveform has been shown to be superior, burst SCS has not been shown to be clinically superior to tonic SCS. While the SUNBURST randomized controlled trial (RCT) showed that burst was statistically superior to tonic, the difference in overall pain was only 0.51 0.40 on a 10 cm visual analog scale (reported as a difference of 5.1 on a 100 mm scale) (4), which is unlikely to be clinically significant (5). In fact, the results indicate that both tonic and burst SCS achieve similar clinical outcomes, which is consistent with the preclinical findings mentioned previously (1,3). Furthermore, burst parameters have not yet been optimized because the parameter space has not been fully explored. The effects of active versus passive charge recovery have not been characterized. Beyond charge recovery, many other parameters can be varied: intraburst frequency, interburst frequency, number of pulses, pulse width, shape, and so forth. With respect to the particular passive charge recovery burst waveform utilized in the SUNBURST RCT, the ProclaimTM Implantable Pulse Generator Clinician’s Manual states that “burst programming parameters for pulse width and frequency were selected from feasibility studies and did not allow subject-specific customization except for amplitude adjustment. Future studies that optimize burst programming may show additional reduction in paresthesia. ” To conclude this discussion, we concur that future research will likely help optimize burst programming as well as elucidate how the physiological changes produced by different burst paradigms are reflected in preclinical behavior and in the clinic.