An experimental pacemaker-like device that delivers jolts of electricity to the neck arteries reduced blood pressure in people for whom drugs did not work, although not as much as its developers had hoped.

Results from a 265-patient study showed the Rheos device was able to help those with severe hypertension - defined as systolic blood pressure greater than 160, reduce it to at least 140 and maintain the lower blood pressure at one year.

The device was implanted in all participants of the study. The research team compared one group in which it was activated with another group of patients in whom it was turned off.

The study, funded by CVRx, showed that 54 percent of those whose devices were turned on achieved the target systolic blood pressure rate after 6 months of treatment compared with 46 percent of the group whose devices were not activated.

The difference was not as great as hoped, but 88 percent of patients sustained lower blood pressure readings at one year, meeting one goal of the trial, said Dr John Bisognano, a cardiologist at the University of Rochester Medical Center and a consultant for Rheos manufacturer CVRx, who presented the study results at the American College of Cardiology scientific meeting.

"The system is safe and its effect is as good as two or three drugs for people who are already taking 5 or 6 drugs and still can't control their hypertension. It's a good additional option for these patients," Bisognano said, noting there are some 125 drugs on the market to treat the condition.

"The drugs available now are good for most people with hypertension, but people with resistant sky-high blood pressure need more. They're in desperate need of additional treatments," he said.

The device is implanted below the collarbone through a small incision and leads are implanted on either side of the neck, requiring two more small incisions. The system works by delivering 4 to 6 volts of electricity, mimicking a spike in blood pressure that activates a natural process called carotid baroreflex that sends blood pressure lower.

There were no unexpected side effects, Bisognano said.

He noted there was a surprisingly large placebo effect and said more studies are needed.

There are other device-based treatments for drug-resistant hypertension that are being investigated. One such technology uses radiofrequency to destroy nerves leading to the kidney.

It works by silencing nerves leading into and out of the kidney which play a central role in the sympathetic nervous system, the body's "fight or flight" response that can increase heart rate and blood pressure.

Hypertension affects an estimated 73 million people in the United States alone and about a quarter of that population cannot control the condition with drugs. High blood pressure raises the risk of developing heart disease, kidney disease, stroke, and hardening of the arteries.