Implantable Seizure Advisory System Has Strong Early Results



In six patients with epilepsy who used an implantable seizure prediction system for at least four months, no seizures occurred during the system’s low advisories and most seizures occurred during its high advisories.

BALTIMORE—Preliminary results indicate that an ambulatory, intracranial EEG may be able to alert patients with epilepsy to periods of safety from and high likelihood of seizures, researchers reported at the 65th Annual Meeting of the American Epilepsy Society. In six patients who used the system for four months, most seizures occurred when the system signaled a high likelihood of seizures and no seizures occurred when it signaled a low likelihood of seizures, said Mark Cook, MD, Chair of Medicine at St. Vincent’s Hospital in Melbourne.

“This is a great advance, because it lets us see something that we’ve never been able to see before—when a seizure will happen,” he said. “This potentially is an opportunity for patients to make themselves safe or possibly even take an acute-acting medication.”
Mitigating Uncertainty

The Seizure Advisory System (SAS) is being developed by the NeuroVista Corporation (Seattle). The system uses continuous EEG monitoring and patient-specific algorithms to inform patients of whether there is a high, moderate, or low probability of an impending seizure. Its most important purpose is to improve the quality of life for patients with epilepsy, Dr. Cook said.

“The uncertainty of when seizures occur is actually the most disabling part of seizures for most people,” he said. “So to have this sort of warning and be able to structure your day-to-day activities around the possibility of seizures would mean a lot to people who want to control their lives.”
The SAS consists of three components: electrodes that are implanted between the patient’s skull and brain, a device that is implanted under the skin of the patient’s chest, and an external device that the patient can hold in his or her hand. The electrodes record the brain’s electrical activity continuously and transmit these data to the chest device, to which they are linked via wire, and the chest device relays data wirelessly to the external device.

Following implantation, each SAS is tailored to the individual patient during a data-collection phase before providing advisories to that patient during an activation phase. During the data-collection phase, the NeuroVista Corporation uploads EEG data from the chest device and, through a machine-learning process, uses these data to program the device with patient-specific algorithms for predicting seizures. During the activation phase, the chest device uses the algorithm to estimate the probability of a seizure and transmits its estimate to the external device. The external device then uses a series of lights—blue for “low advisory,” white for “moderate advisory,” and red for “high advisory”—to advise the patient of seizure likelihood.

Promising Results
In their feasibility study, Dr. Cook and colleagues are evaluating the SAS’s advisory performance, clinical effectiveness, and safety in a cohort of 15 subjects who were implanted with the system at three hospitals in Australia. All subjects were adults who had disabling partial and/or secondarily generalized partial seizures and had failed treatment with at least two anti-epileptic drugs. The subjects had their SAS activated only if, during the system’s data-collection phase, it was deemed capable of demonstrating P values of .05 or less for both high and low advisories and a sensitivity of at least 65% for high advisories.

To date, 11 subjects have completed the data-collection phase, 10 have entered the activation phase, and six have been in the activation phase for at least four months. At four months, none of the six subjects had experienced any seizures during low advisories, and most seizures had occurred during high advisories. The sensitivity of the latter advisories was greater than 65% in two patients—reaching 86% in one and 100% in the other—and it ranged from 56% to 63% in the remaining patients. The system provided high advisories with sufficient notice for patients to prepare for impending seizures. The system’s safety profile was consistent with that of strip electrodes and subclavicular implants, as reported in previous studies.

Future Directions
The researchers are continuing to study the system’s clinical utility in the 15-patient cohort. As only preliminary data have been collected, the NeuroVista Corporation has no plans at present to pursue regulatory approvals.

Although the corporation does not currently intend the SAS to detect seizures for acute therapeutic purposes, this could be a future application of the system, according to Dr. Cook. “We have patients in the trial who are taking their medications acutely when they have a state change on their device, and we’re examining whether that brings about useful change in their seizure frequency,” he said.

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