Renal denervation is an experimental procedure that is being studied to treat resistant hypertension in people whose have been unable to control their high blood pressure with medication.
For Dina*, high blood pressure (hypertension) was a fact of life: her mother, her grandparents, and her great-grandparents all suffered from the condition.
I’ve been on medication for it for years,” she says, but her pressure would still soar, topping 215/100 on many days. “That kind of blood pressure makes you feel like not doing anything,” she says—and the same could be said of the side effects from the many medications she was taking to try to control her hypertension.
About a fifth of us are living with hypertension. Even though it often has no noticeable symptoms, for every five to 10 points of elevated pressure you have, you are at a two- to fourfold increased risk of death from stroke, heart failure, heart disease, or other heart-related condition. Though there is an abundance of treatment options, from lifestyle changes to medications, some people—about 10 percent of people who have hypertension—cannot get relief from the condition no matter what they do. People like Dina, whose blood pressure remains elevated despite being on three or more medications, are considered to have what’s known as resistant hypertension.
Many people who have resistant hypertension become frustrated, even resigning themselves to their condition, but Dina wasn’t willing to settle for that. “I felt like I was going to die, the way I was,” Dina says, “so I took a chance on getting help for myself.” Through Duke’s resistant hypertension clinic, Dina became one of the first patients in an ongoing study of a new way to treat blood pressure at its source—which may not be where you think it is.
Hypertension Starts in the Kidneys
Since so many of the complications of hypertension are heart- or brain-related, many of us don’t think about a key player in the body’s blood pressure regulation system: the kidneys. The kidneys are in constant communication with the central nervous system, and they can release hormones that affect the body’s blood pressure. “One way you can think of hypertension,” says Duke cardiologist Manesh Patel, MD, “is as a disconnect between the kidneys and the brain about what each thinks the body’s blood pressure should be.” In people who have hypertension, the nerves that connect the kidneys to the sympathetic nervous system—the part of the nervous system that controls your “fight or flight” response—are hyperactive, and they prompt the kidneys to release hormones that elevate blood pressure. “That’s how most current drugs work—by trying to block the action of those hormones,” Dr. Patel says.
In people who have resistant hypertension, an experimental procedure called renal denervation may be able to achieve what medications cannot, by mechanically interrupting these hyperactive nervous signals. “The idea comes from an observation made back in the 1930s,” Dr. Patel says. “There were cases where surgeons found that blood pressure dropped significantly after they disconnected the renal [the kidneys’] sympathetic nervous system.”
In today’s take on that procedure, a catheter is fed into the artery leading to the kidney, and an experimental device applies microwave energy to disrupt the nerves between the kidney and the rest of the sympathetic nervous system. Multiple treatments are performed in each kidney artery to disrupt the hyperactive nerves, and then the device is removed.
Duke began studying the device in 2012. The first studies done in Australia and Europe showed promising results. Patel says participants saw their blood pressure drop between 25 and 30 points in the six months after the procedure, and so far they have maintained that reduction in pressure. The first U.S. trial, however, failed to show significant reductions in blood pressure. Trials continue to refine the procedure. And, because Duke is part of the first U.S. study that will help the FDA decide whether to approve the technique for use in this country, people with resistant hypertension continue to be treated with renal denervation at Duke as part of those ongoing studies.
Treating resistant hypertension
Patel emphasizes that, although this new experimental procedure has potential, there is a lot that the team (led by Laura Svetky, MD, and Dr. Patel) does to treat resistant hypertension before a patient is considered for the new trial. “Managing complex blood pressure is difficult for both the patient and the physician,” he says, “so before we even consider a patient for an experimental trial, we use a careful, stepwise approach to examine all the possible factors that contribute to the condition.”
First the team looks for any underlying causes, he says. Things like sleep apnea, kidney disease, or problems with the adrenal glands can all contribute to hypertension, and successful treatment of such disorders can improve blood pressure.
If underlying diseases aren’t a factor, then the team assesses the patient’s medication history and tries to determine the best possible combination of medications for that person. “We aim to start patients on a diuretic, followed by other types of medications,” Patel says. But he explains that it can be difficult for patients to comply with certain drug regimens. “Many of our patients have often tried many drugs in many combinations,” he says. “If a regimen doesn’t work, most of the time it’s due to side effects that are intolerable; but sometimes the regimen itself is so complex that it’s easy to make mistakes about what pill should be taken when.”
Patel says that Duke’s resistant hypertension clinic has helped many people reduce their blood pressure and that this experimental trial is a particularly exciting part of their approach for people who would otherwise be at a dead end. “When a patient has been on multiple medications, and the medications have failed to work, previously there weren’t a lot of other options,” he says. “This technique has the potential to lower a patient’s lifetime blood pressure.” Adds Dina: “It’s really helped me. I want other people to know that it’s there to help them, too. I want to say to them, go for it. Be encouraged.”
*Last name omitted for privacy.
Hypertension and Resistant Hypertension: What’s the Difference?
You are diagnosed with high blood pressure (hypertension) when you have consistent blood pressure readings of 140/90 or greater. doctors know that sometimes a person’s blood pressure goes up just by being in the doctor’s office (called the “white coat effect”), so they’ll often do multiple readings to confirm a diagnosis of high blood pressure.
You could have resistant hypertension if you have a blood pressure of 160/90 or higher and are on at least three medications, including a diuretic.