I'm a neurosurgeon from Portland, Oregon, and I'm going to talk about waveforms. So before I start, the concept of waveforms in spinal cord stimulation or neuromodulation is very similar to the concept of dosing of pharmaceutical drugs. So you don't administer medications in a single-dose, single format for all patients. Waveforms for neuromodulation is similar to that. For the very long time, we've been administering neuromodulation in a single-dose, in a single format, and only in the last maybe five years, we started to realize that there is this field of electroceutical, very similar to pharmaceutical. What I'm going to just talk about is the very primitive principles of this, and I will introduce you to the available different waveforms in the four most widely spread used commercial brands. So these are my disclosures. Some of them are actually relevant to this. You know pain is a big problem, about $100 billion a year of lost productivity. It's many, many Americans. It's the most common presenting symptoms for many, many primary care physicians. When we treat pain, we just have an ablation concept or a neuromodulation concept. Spinal cord stimulation is a testable, adjustable, reversible, and a neuromodulatory therapy, and each one of those actually warrants its own lecture. There are very few therapies that are testable. We don't actually, when we do spine surgery, when we do any treatment for pain or microvascular decompression, we don't have a way to test whether the therapy will be effective. It's also not adjustable. This is something that you can tune up. You can increase, decrease. You can adjust the therapy, and you could stop it or remove it if you want to, and it changed the entire nervous system. It's not a temporary ablation. It changed the network, and it's the most common form of neuromodulation. There's about 10 spinal cord stimulators placed for every other therapy of neuromodulation, including VNS and DBS combined. So spinal cord stimulation is a market of its own. So this is the evolution of the therapy. This is started in 1976, Malshek and Wall, the gay theory, and a few weeks or maybe a few months afterwards, Shealy implanted a spinal cord stimulator. He put it intradural. This is the very first stimulator that was implanted intradural, and the patient dies like three days later or a few days later. This was a cancer pain, but nevertheless, this was the onset of therapy. And then percutaneous electrodes were invented later, and then self-powered battery, and then programmable quad electrodes, primary cell battery, and then rechargeable. So this was the history, and from 2004, the field was kind of stagnant. There's nothing happening. We have learned that the distribution of electrical field in the spinal cord depends on the proximity of the dorsal column, the CSF space, and the type of electrodes. And we knew where to map, you know, where in the spinal cord we could induce paresthesia that will lead to pain relief. So unlike the conventional dermatomal distribution in which if you want to target L5, you have to go to the nerve roof of L5, to target this in the spinal cord, you have to be much, much higher up. You have to be in the lower thoracic spine. And then the first prospective multicenter trial was in 1996 by my senior mentor. So all the way up to 2015, there was no way form of frequency manipulation. All spinal cord stimulation was administered through what's called a tonic stimulation. It's a regular stimulation like this, beep, beep, beep, with only ability to change the amplitude and maybe the pulse frequency. Spinal cord was the only target. You could not target nerve roots. You could not target other parts. They were not MRI compatible. Once you get a spinal cord stimulator, you can't get an MRI, and there was no wireless connection to the system. You had to actually make physical proximity contact. You had to bring the stimulator in proximity to the battery, to program it to the battery to be able to connect to it. And this is because we have relied heavily on the concept that paresthesia is so crucial to achieving pain relief. But the problem with getting paresthesia is there's numerous, numerous problems. Number one, obtaining paresthesia in the back is not easy, as well as obtaining paresthesia lower down in the foot. So the extreme averages of where you try to stimulate the upper back and the lower feet is areas that it's hard to capture stimulation. There's change in the amount of paresthesia with positioning. So patients, when they extend or flex, if you have a percutaneous electrode or you have a parallel electrode, there's change in paresthesia. And some patients would not tolerate paresthesia, especially patients with complex regional pain syndrome. So patients with allodynia or hypoalgesia, you turn on the paresthesia and they would not tolerate this. And additionally, there's patients that have a very narrow therapeutic window. So therapeutic window means the range between the onset of benefit to the onset of complication. Some patients have a very wide therapeutic window in which you could turn on the stimulation at one volt and you get paresthesia and you perceive benefit, and then they don't perceive complications such as untoward stimulation, such as contractions or feeling excessive pain until maybe eight volts. But some patients, they have a very small therapeutic window. In other words, you turn on the stimulation and immediately the field side effects. For these reasons, paresthesias were helpful for the most part, but for a subset of patients, paresthesia worked against you. So this is the conventional tonic. Most spinal cord stimulation, we used to use frequency in the range between 30 and 60. We used about 40. And then the pulse width was about 200 microseconds. But everybody got this. When you change, you change it by maybe 10 hertz up, 10 hertz down, but you don't change that much. Until this is the first thing that came out. This is what's called HF10, which is very high frequency stimulation. High frequency that's 10 kilohertz, 10,000 kilohertz stimulation. It's not a physiologically guided stimulation. In other words, there is no cell in the body or there's no network in the body that oscillates at that frequency. The fastest cell in the body is about 300 hertz, and that's because the action potential duration is about three milliseconds. So you can't really, you can't do faster than 300 or 350. So nevertheless, this frequency achieved pain relief and did not lead to any paresthesia. There's also something else about frequency, which is the waveform characteristic. You look at the second one from the left. This is called charge balanced waveform, in which the positive amplitude is very similar to the negative amplitude. And generally speaking, we want to use charge balanced waveform, because charge balancing is not neurotoxic. If you accumulate therapy only in one direction, that can lead to neural ablation. So the kilohertz frequency was introduced by a company called Nevro, and there's multiple studies that show that this is very effective, and it's very effective in treating back pain as well as low back pain. The amplitude is one to five milliamps, and the frequency is 10 kilohertz, and the pulse width is about 24 to 30 microseconds. This specific paradigm by the company is heavily guided by the manufacturer. As a physician, you have little control in how much you change. You can maybe change the amplitude, but you can't change more than that. You cannot turn that into a lower frequency. And the placement is recommended to be around T9, 10 disk space. So in these cases, trial is only for therapeutic efficacy, is not to find the sweet spot on the spinal cord. When we do a spinal cord stimulation trial, we want to answer two questions. Is there a sweet spot that we need to target? And number two, is this effective or not? For high frequency stimulation, the purpose of trial is only to determine whether it's going to be effective, because you have to put it in the same spot everywhere. And there is some data from other manufacturers that actually procedure mapping is not that important. You can just go for an atomic placement. This is the first study that was published in 2015, and there's a follow-up study published in Neurosurgery for a 24-month follow-up that shows that high frequency stimulation is superior to conventional spinal cord stimulation. It's effective in back pain, as well as leg pain. And that's the long term. The second different type of waveform manipulation is what's called burst stimulation. And that's a little bit different than, we're not looking at how fast we're running the stimulation. We're looking at how regular we're running the stimulation. Burst stimulation is a regular stimulation that has a pattern. In physiological systems, there's actually only three ways to deliver waveform pattern. Either deliver them in a tonic, meaning regular stimulation, beep, beep, beep, very similar to the heart rate, or you can deliver random, or you could deliver a burst. And a burst stimulation, meaning there's an accumulation of activity followed by a little pause, followed by an accumulation activity. There is actually a definition of a burst, and that's the inter-spike interval follows what's called Poisson distribution and histogram. I'm not going to need to go into the basic science of this, but burst stimulation is the way most physiological systems connect, because it turns out that our brain learns from altering signals. So tonic firing, meaning regular firing, doesn't provide a lot of information, but change in the pattern of stimulation provides a lot of information. So this is the thalamic firing in the bottom, that's the burst stimulation compared to tonic, and that's what inspired Dr. Dirk De Ritter, who patented this form of stimulation. He patented this particular form, I'm going to talk a little bit about this. This particular form is called burst DR, which is 500 hertz cycled 40 times. These are five spikes, each one of them is one millisecond with one millisecond inter-spike interval. It is not charge balanced. This is a non-recharge balanced, but the recharge balancing occurs after the five spikes. So because there are five spikes, each one of them is one millisecond with one millisecond inter-spike interval, the duration of those five spikes total is 10 milliseconds. There's a 15 millisecond interim between the next burst, which makes the duty cycle 25 milliseconds, and that's why it's 40 hertz, so it's 40 times because of this. This particular form is called burst DR, not that there's any other burst, you could cycle 30 over 600, you could cycle, you could have any combination. This particular form is what was studied the most and was found to be most effective. I think Dr. Dritter, when he did this, he tried 1,000 hertz, he tries 1,500, he found that this is the most energy efficient and also it's the most effective. What's also very important about this particular form of stimulation compared to many other forms of stimulation, most changes in waveforms are towards the direction of more energy. I'm going to give more frequency, I'm going to give more density. This is kind of the opposite, this is actually lower energy. You are giving a duty cycle of 40 percent, so it's only 10 seconds out of 25 milliseconds, and also this is further cycled, so when we turn that on, it's not on all the time, it's cycled. So this is a low energy stimulation, which has an implication of what kind of battery to choose. You don't need to have a rechargeable battery, which we know also it has an impact on the compliance of charging, which has an impact on how long the therapy would last. Why do we think BIRST works? Because it impacts more than one system. There's a lateral and medial pain pathway, the affective component as well as the sensory component, so the BIRST stimulation impacts both. This is what's shown by quantitative EEG in the original BIRST trial, and this is also shown by subsequent analysis of what's called the SunBIRST trial, which is the pivotal trial by the FDA to approve this. Again, BIRST stimulation works better than spinal cord stimulation for back pain as well as leg pain, and this is the results of the SunBIRST trial that shows that it's not just non-inferior, it's actually superior to conventional spinal cord stimulation. Is this the only thing we could do? Can we just do very high frequency and all the only BIRST? No, we can do other things. You could do multiple technical forms, so you could cycle. If people here who do anything other than spinal cord stimulation, you know that vagus nerve stimulation, for example, is cycled. It's cycled 30 seconds every five minutes, so it's not on all the time, so you could cycle stimulation. You could increase the frequency. It doesn't have to be 10 kilohertz, but it can be 1,000, it can be 500. Actually the threshold for loss of paresthesia is around 800 hertz, so anything above that, you don't have paresthesia. And this is the paradigm by a third company. This is by Medtronic. This is called High Density, paper by the suite right here. And then the idea here, again, back to the physics principle, we look at what's called area under the curve. If the area under the curve is large, that means you're delivering a lot of charge. So wide pulse widths and high frequency, meaning you're delivering a lot of energy. When you deliver a lot of energy, such as high frequency, 10 kilohertz, or high density, the battery cannot sustain that for years. You have to use a rechargeable system. The implication of using high energy, that you can't use a single cell battery. There's what's called Evolve Workflow. It's also effective, and I've used it, and it's very similar to high frequency stimulation and burst stimulation. And then the last thing, this is by Boston Scientific, in which they have a battery that can combine all these. So you don't have to choose. If you want to do tonic, choose the one on the top. If you want to do burst, choose the one in the middle. If you want to do high frequency or high density, choose the one on the bottom, and you could cycle through this. I personally don't use this. I use one form of therapy because I think the brain, if you use all those, then you burn all your bridges. I would like to use one therapy, and if it fails, I go to the next one, and I go to the next one. So if I introduce all three at the same time, I wonder if this just burns. I don't have any salvage plan if I do this. But that's just my personal opinion. There's no studies that was shown to this. Nevertheless, their Lumina study shows that this is more effective than conventional spinal cord stimulation. So there is evidence to back all these different waveform manipulations. So the four ones are high frequency, 10 kilohertz, burst stimulation, evolve, or high density, or the Lumina, which is a combined therapy. What do we learn from all this? One size doesn't fit all. When you decide to administer therapy to the patient, you need to know the advantages of each manufacturer. You need to know which system is MRI compatible and which system is MRI compatible for which part of the spine. Like, for example, Abbott, they produce the burst stimulation, and the battery can do burst as well as tonic, but at the same time, it's only MRI compatible from T7 to T12. It's not MRI compatible from the cervical spine. While the Medtronic system, for example, is MRI compatible in the cervical spine as well as Boston. Now, so every company has a leg up and a leg down. You need to know what you're trying to use, what you're trying to achieve here. How old is the patient? What's the lifelong need for getting an MRI? And whether the patients have CRPS, do you need prosthesia or not? Does this patient prefer prosthesia? So I actually put all these in my paradigm for choosing the therapy. We need to discuss all brands. The battery choice is important, the lead type is important, and the stem choice is important as well as MRI compatibility. I talked about the difference of cell therapy. There's many, many, many leads you can choose, but most of us who do this usually have one go-to lead. So my go-to lead for Abbott is the Penta, is the 5x4. My go-to lead for Medtronic is 565. One of them is, and leads are designed with the company's concept therapy. If you look at the right-hand side on the top, this is called the 565. This is the Medtronic. It has a tapering end and it's a little curved, so it actually fits very well on the spinal cord. The concept behind the lead that it covers two vertebral segments. So it's forgiving in terms of which level you want to approach. On the other hand, Abbott, which is the bottom on the right side, these are wider. They have more versatility on the width. Medtronic have more versatility on the height, while Abbott have more versatility on the width. And this is how you're thinking about your targeting. People who use Abbott think that back pain fibers are more lateral on the spinal cord and to get back pain fibers you need to be lateral. People who use Medtronic think it's important to be in the sweet spot in the vertebral level. That's why they want to cover more. So your philosophy and care will actually dictate which lead to go to. There's also more choices. We can choose between DRG and spinal cord stem. We can choose between tonic, burst, high HF, and high density. And the MRI compatibility, you actually need to update yourself on which company is MRI compatible for which lead and which battery for which level, because this keeps changing every six months. And then you need to offer patients other options. Sometimes I would send my patients, tell them, you know, go see my spine partner before you come to me. And if you want to do this on the right time, fine. Do this big, big wax spine fusion. But I suspect you're going to be back to me. In conclusion, neurostimulation for chronic pain has undergone a revolution. And can and should be tailored for individual needs. Multiple technologies provide options and challenging our fixed beliefs. This is a good time for neuromodulation because there is more technology coming up. Thank you. Do you have any questions for Dr. Roslin? I would like to say that, you know, if you're just learning how to do this in your practice, there are so many options. I think just sometimes breaking it down into just basic things or, you know, I like to think simply. So for me, sometimes it's just as easy as which reps are going to be there reliably for your patient. What do you have access to? If I have a patient, for example, who is a cancer patient and is going to need a lot of MRIs, well, Medtronic is phenomenal for all types of MRIs. If I have a patient who has really specific limb pain, but also back pain, and I'm thinking maybe they might need DRG in the future, then maybe I'll go with Abbott and then consider having one rep so I can do a spinal cord stim and then maybe do a DRG later on and they have the same company. I mean, there are a lot of different reasons to use all of them. I personally use all of the companies probably equally. I personally think that over time they're all pretty much equal. You know, it just really depends on how you use it. I'm kind of a nerd and I like to really know what the reps are programming my patients with. If something doesn't work, I want to make sure I know which disc space they're using, try a different area or a different level, or are they using paresthesia-free, are they using paresthesias? It's just important to know the nuances, but you don't have to get overwhelmed by it, just, you know, as long as you're kind of familiar with the different types, then I think it's easier to choose what you want in which scenario. Did you have a question? So at this point, we have a lab session. We don't have cadavers this year, so this will be fun. Some of these are different simulation options.

neurosurgeon

waveforms

spinal cord stimulation

personalized dosing

evolution

chronic pain