Innovations related to electrodes and pacemakers (IPG)
The most important factor in the success of brain pacemaker treatment is the precise placement of the electrodes in the target nucleus in the brain, usually an area responsible for motor function in the subthalamic nucleus (STN- SUBTHALAMIC NUCLEUS).
Ideally, the electric field created around the implanted electrode affects only the structures involved in Parkinson's disease and the slowness, stiffness, tremors and more can be improved without side effects. However, near the motor part of the STN nucleus there are other areas that affect other important brain functions, so if the electrodes are not placed in the center of the motor area of the STN, the electrical pacing may cause, among other things, unwanted side effects such as difficulty speaking or changes in mood due to the effect of the electric field on adjacent areas outside the target area.
Therefore, before performing the surgery, special imaging tests are performed using a high-resolution MRI in order to identify the target nuclei deep in the brain and to plan the route of inserting the electrode in the surgery. In addition, in order to verify the position of the electrodes in real time, recordings of the neural activity from deep within the brain are made during the surgery using fine electrodes (micro-electrodes) which are able to record the activity of individual neurons. These recordings help identify brain activity characteristic of the STN nucleus in Parkinson's disease.
When the electrode is optimally placed in the brain, we can more easily control the parkinsonian symptoms of stiffness, slowness, tremors, etc. and theoretically without side effects.
After the operation, the patient comes to a neurologist specializing in movement disorders and DBS pacing in order to program the pacemaker so that the electric field includes as much as possible the target area involved in the disturbing symptoms and includes as few areas whose pacing can cause side effects. The range between the intensity at which a good effect on the symptoms is achieved and the intensity of stimulation at which side effects appear is called the "therapeutic window" (a sort of window of opportunity for treatment).
In recent years, there has been significant technological progress in the field of DBS and, among other things, technologies have been developed that allow us to increase the therapeutic window, meaning that they allow us to more easily pace the desired tissue and achieve good control of the parkinsonian symptoms, while reducing the side effects.
I will now mention 2 main technologies that arrived in Israel.
- Directional Leads
- Sensing technology/ open circuit. Sensing
1. Multidirectional electrodes: The classic electrodes used for pacing in Parkinson's contain 4 identical ring-shaped contacts (360 degrees) that are placed one above the other at regular intervals. Of these, one or two contacts are activated that are located inside the target site. When the contacts are activated, the electric current spreads spherically (spherically) in all directions (Figure 1). In this situation, if the electrode is deviated by a millimeter or two from the center of the target, the tissue that will be affected by the electric current may also include nearby areas whose stimulation can cause side effects.
The multi-directional electrodes are built so that their two middle contacts are divided into 3 sub-contacts (drawing 2) so that each of them can be controlled and activated separately. In this way, the generated electric field can be shaped which now does not have to be a symmetrical sphere but can deviate in a certain direction (Figure 3). The rationing using the multi-directional electrodes is called in English STEERING from the word steering wheel, the electric field can be rotated like a steering wheel in a car which allows me to turn in different directions (Figure 2).
In fact, in early studies that tested the effect of activating a spherical field (3 contacts that create 360 degrees) compared to the activation of a directional field by using only one or two contacts out of those three at the same height, they found that activating an electric field by one or two contacts (less than 360 degrees) ), found that the activation of an electric field allowed rationing for better efficiency and that it involved fewer side effects. That is, a larger therapeutic window was obtained by using a directional rationing technique.
2. Sensing technology/open loop:
As mentioned at the beginning, in order to verify the placement of electrodes during the surgery, 2 dimensions are taken into account. Anatomical dimension - by using advanced imaging before and after surgery and a physiological/functional dimension - registration and identification of brain cell activity with certain characteristics of Parkinson's disease in the target area where the electrodes are desired to be implanted. In Parkinson's patients, the brain activity in the STN nucleus is characterized by pathological activity in the frequency of "beta waves" (20-30 Hz) and when it is detected during surgery, we know that the electrode is located in the target area.
Until recently, it was not possible to continue to record the brain activity in the paced area after the implantation of the permanent electrodes.
In recent years, researchers have developed technology that makes it possible to continue to record brain activity also from the permanent electrodes implanted in the brain and connected to the DBS pacemaker. One of the challenges was to overcome background noise and still receive signals in real time and during patient activity.
In the last year the aforementioned technology was approved for clinical use and today we have electrodes that are connected to a pacemaker and are able to record for certain periods of time the activity of the beta waves that express the "parkinsonian" activity in the brain. The goal is that by using recordings of the brain's activity in real time, we will be able to find out which of the 4 The contacts at the end of the electrode are optimally placed within the target nucleus. In addition, we can test the effect of the pacing on the "parkinsonian" pathological activity in the brain and adjust the pacing so as to change it back to a physiological (normal) configuration. Until today, these decisions were made by clinical examination of The patient and evaluation of the degree of stiffness, slowness and tremor. Information obtained from the brain itself can help and direct us better and faster to the preferred pacing parameters, a process that can take several months.
It should be noted that at this stage the technology is still new, there are still many unsolved therapeutic questions and there are no regular therapeutic algorithms for clinical use and for making decisions derived from the information received.
The vision is that in the future the pacemaker itself will be able to process the input from the implanted electrodes and adjust the pacing in real time to the patient's needs in an optimal way, while combining the two technologies- sensing and directionality.
