Zapping Kidney Nerves Lowers Drug-Resistant High Blood Pressure
A minimally invasive non-drug treatment that delivers radio waves via a catheter probe to “zap” and thereby deactivate nerves in the kidney arteries, appears substantially to reduce blood pressure in patients whose hypertension does not respond adequately to medication.
These were the findings of a clinical trial presented at the American Heart Association’s Scientific Sessions 2010 in Chicago on Wednesday. A paper on it was also published online in The Lancet on the same day.
The name of the trial is Symplicity HTN-2: International, Multicenter, Prospective, Randomized, Controlled Trial of Endovascular Selective Renal Sympathetic Denervation for the Treatment of Hypertension and the principal investigator is Dr. Murray Esler, associate director of the Baker IDI Heart and Diabetes Institute in Melbourne, Australia.
Up to one in five patients receiving treatment for high blood pressure remain at risk of heart attack, stroke and other hypertension-related problems, because even if they take several drugs, their blood pressure is not lowered enough.
In this late breaking trial, Esler and colleagues found that silencing the nerves near the kidneys significantly reduced blood pressure in patients whose blood pressure was still too high, despite taking an average of five medications to control hypertension.
The trial is the first human randomized controlled trial of a minimally invasive procedure called renal denervation or RDN, used for therapeutic reasons.
In RDN, doctors insert a catheter-based probe into an artery in the groin, and then guide it up into the renal artery where it emits a short burst of high frequency radio waves with enough energy to deaden small nerves that run along the lining of the renal arteries and are linked to high blood pressure.
In the Symplicity HTN-2 trial, Esler and colleagues randomly assigned 106 patients to receive either RDN plus medication (52 patients) or just medication (54 patients).
The average age of the participants was 58 years, 35 per cent were female and 97 per cent were Caucasian.
Blood pressure measurement comprises two numbers, for example 140/90 mm Hg (“mm Hg” stands for millimeters of mercury). The first and higher number represents systolic pressure, which is the pressure against the artery wall when the heart beats, and the second and lower number is the pressure between beats, the diastolic pressure.
At the start of the trial the patients in both groups had nearly the same levels of average blood pressure: 178/98 mm Hg for the treatment group versus 178/97 mm Hg for the controls.
Six months after treatment, the systolic blood pressure (the higher reading) of the group that had the catheter procedure fell by an average of 33.4 mm Hg and their diastolic pressure (the lower reading) dropped by an average of 12.5 mm Hg.
In contrast, the average systolic blood pressure of the controls rose slightly (0.9 mmHg) and their average diastolic pressure fell slightly (0.3 mm Hg).
At the time the news was released to the press, Esler said they had complete data on 48 of the RDN patients, and that of these, 93.8 per cent had experienced a systolic blood pressure reduction of at least 5 mm Hg and 87.5 per cent had seen a drop of at least 10 mm Hg in this same measure.
Also, about 39 per cent of the treatment group, compared to only 6 per cent of the controls, experienced a drop in blood pressure to below 140/90 mm Hg, the threshold that is normally used as a target in hypertension treatment, which is higher than the 120/80 mm Hg considered ideal for adults.
It is very unusual for people with severely drug resistant high blood pressure to reach the target with drugs alone, said Esler.
He also told the press that:
“In a small minority of patients in the study, some high blood pressure medication could be stopped or reduced”.
“The procedure safely and successfully silences the nerves for six months, and perhaps permanently,” added Esler.
He said the procedure provided a revolutionary non-drug treatment for patients whose high blood pressure is not responding adequately to “multiple antihypertensive drugs”.
Although nearly all the participants were Caucasian, Esler said he expected the findings would have been no different for an ethnically diverse group.
He and his colleagues found no serious device or procedure-related side effects, and there were no cardiovascular or kidney-related complications.
Ardian Inc. of Mountain View, California, who make the Symplicity Catheter System used in the RDN procedure, funded the study, and Esler also declared receiving consultancy funding from the company.
The British Heart Foundation (BHF) said in a statement that they hoped the study could lead to new treatments to reduce illnesses and deaths linked to high blood pressure.
Dr. Jeremy Pearson, a professor and associate medical director of the BHF said:
“This trial opens up a potentially exciting new avenue for the treatment of patients with high blood pressure who do not respond well to current medicines.”
“Further studies are needed to see if this invasive procedure will be acceptable to patients and produce long-lasting effects that are safe and reduce future cardiovascular events,” he added.
Dr. Suzanne Oparil, director of the Vascular Biology and Hypertension Program at the University of Alabama at Birmingham in the US, told Cardiology Today that:
“This is an extremely important study with a number of great strengths and the potential for really revolutionizing the way we deal with treatment-resistant hypertension.”