November 18, 2010
Radio Waves Lower Blood Pressure: Study
A quick blast of radio waves to the nerves of the kidneys can help control high blood pressure in patients who do not respond to conventional treatment, researchers reported on Wednesday.
The device works by selectively severing nerves leading to the kidney that play a key role in regulating blood pressure. In the study, the radio waves effectively lowered the top blood pressure reading by an average of 32 points after just six months, versus no change in those who took the best available medications.
Normal blood pressure is 120 over 80 or lower, while a top reading of more than 140 is considered high blood pressure, which means the blood is exerting excessive force against the vessel walls.
The condition, which affects some 75 million Americans, is the leading risk factor for premature death. However, just two-thirds of those people are treated, and only half of those treated are actually able to get their blood pressure under control.
The device under study, made by Mountain View, Calif.-based Ardian Inc., works by disrupting nerves leading into and out of the kidney. These nerves play a vital role in the body's "fight or flight" response, or sympathetic nervous system, which can raise blood pressure and heart rate.
"There are a lot of questions, but it is very exciting," said Dr. Suzanne Oparil of the University of Alabama at Birmingham in an interview with Reuters.
Although procedures that surgically silence these nerves had been shown decades ago to lower blood pressure, they were discarded with the arrival of drugs that target the renin-angiotensin system, which controls blood pressure and fluid retention.
"Those drugs are good but not perfect," said Dr. Murray Esler of the Baker IDI Heart and Diabetes Institute in Melbourne, Australia.
"We can see that because of their failure in the patients on this trial. They are all on drugs of this type," said Dr. Murray.
The treatment uses a catheter that is inserted through a puncture in the groin area. The tiny tube is then woven through blood vessels into the artery leading to the kidney. Once the device is set in place, it applies short bursts of low-power radiofrequency waves that destroy the nerves lining the vessel. The device continually rotates to ensure no area receives too much energy.
In the study, roughly half of the 106 patients were randomly selected to have the procedure in addition to their medications, while the other half took only medication.
"They were sick hypertensives on an average of five medications in both groups," said Esler.
After six months, blood pressure among those who received the treatment fell by 32 points on the systolic and 12 points on the diastolic reading, moving some patients into the near-normal range. There was no change seen among those in the control group.
"It was a big effect," Esler said.
"The main pressure in the group after denervation was 145, and in 39 percent of them, it was 140 systolic."
"It's a much bigger effect than you would anticipate in a drug trial, particularly in these people, who are resistant to drugs anyway," Esler said.
The device seems to be very safe, Esler added.
"The side effects of the trial were almost zero."
Nevertheless, it is not a cure, he said.
"Most of this group are still on medications. They are not cured. If you tried this out on milder hypertensives, maybe you could cure it. That is a dream, but we are thinking about it."
The treatment is already approved for use in Europe, and Ardian CEO Andrew Cleeland said the firm is in discussions with the U.S. Food and Drug Administration to establish a late-stage U.S. trial that could begin next year.
The procedure costs roughly 10,000 euros, or about $13,500, Cleeland said.
The findings were presented at a meeting of the American Heart Association in Chicago, and were described in The Lancet medical journal. A summary can be viewed here.
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