Implantable Device that Blocks Brain Signals Shows Promise in Obesity

Pauline Anderson

July 09, 2008

July 9, 2008 — A pacemakerlike device that uses high-frequency electrical currents to block brain signals to the stomach and pancreas through the vagus nerves helps patients lose excess weight, without the aid of dietary or other lifestyle interventions and with no significant adverse effects on heart rate or blood pressure, according to results of a new open-label study.

Patients who had the device implanted for 6 months lost an average of almost 15% of their excess body weight, while about one-quarter lost about 25%. Three patients lost more than 30% of their excess weight.

The new therapy, called intra-abdominal vagal blocking (VBLOC), has several advantages over existing weight-loss strategies, said Michael Camilleri, MD, professor of medicine and physiology at the Mayo Clinic in Rochester, Minnesota, and co–lead author of the study. "First, it's minimally invasive and in fact can be done entirely with the laparoscope or keyhole surgery; second, it doesn't produce any change to the anatomy or the routing of the food through the upper digestive organs; and third, it is completely reversible."

The study, which appears in the June issue of Surgery, is the first of its kind in humans.

 

International Sites

The 31 patients in the study were from centers in Mexico, Australia, and Norway. They were aged 25 to 60 years and had a mean body-mass index (BMI) of 41.2 (range, 38 – 48). None had achieved satisfactory or sustained weight loss with diet, behavioral interventions, or pharmacotherapy.

 

No US center took part in the study. This was to avoid any possible conflict of interest, since the Mayo Clinic was involved in the "conceptualization" of the device, said Dr. Camilleri, who helped design the study. "We also wanted to be available for any tweaking of the protocol," he said.

For the open-label study, doctors surgically implanted lead wires into the abdomen of each patient, attached electrodes to both vagus trunks, and suspended the neuroregulator in a layer of fat in the anterior abdominal wall. The device was then programmed to be on for 5 minutes and off 5 minutes for 12 consecutive hours (it was turned off at night).

Scrambling Messages

The device works much like a pacemaker, which sends electrical signals to the heart to ensure optimal rhythms. "The principle here is quite similar," said Dr. Camilleri. "In some respects, it's like sending a scrambling message into the vagus nerves to stop them from doing what they would normally do after we eat."

Blocking the vagus nerve achieves 3 major goals, Dr. Camilleri explained to Medscape Neurology & Neurosurgery. "The first is to stop the contractions of the stomach and therefore prevent the efficient and rapid breakdown of food; second, by blocking those contractions, we also slow down the emptying of food from the stomach, and third, we block the production of enzymes that are necessary to digest the food."

Researchers followed the subjects weekly for 4 weeks, every 2 weeks until 12 weeks, and then monthly, assessing body weight; physical parameters, including electrocardiograms (ECG); and adverse events.

They calculated the percentage of excess weight loss (EWL) by dividing weight loss by excess body weight and multiplying by 100.

Mean excess weight loss at 4 and 12 weeks and at 6 months was 7.5%, 11.6%, and 14.2%, respectively (all P < .001). Some 25% of patients lost more than 25% at 6 months, with the maximum being 36.8%.

This kind of weight loss is about what is expected following a lap-band procedure but not quite in the higher range of weight loss typical after a gastric-bypass procedure, said Dr. Camilleri.

Variable Response

 

These results are nonetheless very good, especially considering that the study did notinclude behavioral modification, dietary advice, or drug therapy, said Dr. Camilleri. "We haven't maximized the potential for this treatment yet."

The device might work even better using a different — perhaps more efficient — algorithm to send electrical signals, said Dr. Camilleri. "For example, what if instead of having the device on for 5 minutes and off for 5 minutes, we had it on for 10 minutes and off 5 minutes?"

But the device did not work as well for all patients, perhaps due to the variable positioning of the device. As some people lost weight, the contacts for the batteries suspended in their abdominal fat became less secure, ultimately affecting the quality of the electrical signals. This glitch has since been corrected, said Dr. Camilleri.

There were 2 subgroups to the study. In 1, 10 patients from the center in Australia filled out diet records at various stages. That investigation found that calorie intake decreased by more than 30% at 4 and 12 weeks and at 6 months (P < .01). Patients also reported reduced hunger and earlier satiation at mealtime.

"Chew-and-Spit" Test

In the other subgroup, 24 patients participated in a "chew-and-spit" test, in which investigators measured blood levels of the hormone pancreatic polypeptide (PP) after patients chewed food but did not swallow it. "People who had good vagal blockade had about twice as much weight loss as people who didn't have as good vagal blockade," suggesting that it was the vagal blockade that was influencing the weight loss, said Dr. Camilleri.

There were 3 adverse events requiring a brief hospitalization, but none were related to the device. There was only a slight drop in blood pressure, and no clinically significant changes in ECG findings — only a small decrease in heart rate.

 

Patients in the study will continue to use the device until they reach their weight-loss goal. Since it is made of materials that have been used for at least 30 years in pacing wires and batteries, the safety of the device is not in question, said Dr. Camilleri. "There is no significant risk associated with these foreign objects in the body."

Another much larger trial of the device is getting under way. In that study, all patients will have the device implanted but will be randomized to either have it switched on or off. That study will look at a number of outcomes, 1 of which is weight loss at 5 years, said Dr. Camilleri. However, he added, since medical devices in the United States are regulated somewhat differently from pharmaceuticals, it's conceivable that the collected data from that study will be reviewed well before that time.

The study was supported by grants from EnteroMedics, developer of the VBLOC therapy. Dr. Camilleri reports receiving consulting fees as part of a business alliance between the Mayo Clinic and EnteroMedics.

 

Surgery 2008;143:723-731. Abstract

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