November 20, 2012 - By Jessica Shugart
Researchers at the Stanford University School of Medicine are seeking participants for a clinical trial testing the effectiveness of a minimally invasive procedure designed to help patients with high blood pressure that’s resistant to treatment.
Treatment-resistant hypertension, defined as blood pressure that remains high even in patients taking three or more medications, is a serious health threat to an estimated 6 million Americans and 100 million people worldwide. Unchecked high blood pressure is associated with increased risk for heart attack and stroke, as well as kidney disease and heart disease. It is estimated that 28 percent of patients treated for hypertension are resistant to medication. For these people, few other options exist.
The device being used in the clinical trial — called the Symplicity catheter system — works by dampening signals from nerves near the kidney, which are known to regulate blood pressure.
The Symplicity system, manufactured by the medical-device company Medtronic, was approved for use in Europe and Australia in 2010 based on the positive results of smaller trials. While four other renal denervation devices have received approval in Europe, currently none are approved in the United States, and the Symplicity system is the furthest along in clinical development. The U.S. trial will test the effectiveness of the procedure in American patients, with the goal of gaining FDA approval. Of the 530 patients enrolled in the multicenter trial throughout the country, 50 participants will be treated at Stanford.
“This procedure offers hope for those folks who’ve been unable to get their blood pressure under control with medications alone,” said David P. Lee, MD, associate professor of cardiovascular medicine and lead investigator for Stanford’s portion of the trial.
Medtronic is funding the clinical trial, and will cover the costs of the procedures and all clinic visits.
The procedure — called renal denervation — de-activates a portion of the nerves in the renal artery that are involved in the regulation of blood pressure. First, a catheter is inserted into the femoral artery (in the groin), and threaded up into the renal artery next to the kidney. Low-power radio frequency energy is then delivered through the catheter, resulting in the selective takedown of some of the nerves in the area. The whole procedure takes less than an hour, and patients go home the following day.
Although it may seem odd that renal nerves control blood pressure, researchers have been aware of the connection for some time. “There’s a complex interplay between the brain and the kidney that regulates blood pressure,” said Lee. “In people who have difficulty with high blood pressure, that axis between the organs is disturbed.”
In the past, renal denervation was accomplished through surgery by directly cutting the renal nerves. In addition to the drawbacks of invasive surgery, the main issue with the nerve-slicing procedure was that it worked too well — patients went from having high blood pressure to having dangerously low blood pressure.
The Symplicity device works by inactivating only some of the renal artery nerves rather than wiping out all of them. “We’re basically turning down the volume of the nerves. Instead of going to zero and muting them like the surgeons were doing, we’re turning it down to the middle,” said Lee.
The hope is that this measured reduction in renal nerve signaling will lead to healthy blood pressure in patients who have exhausted all other options.
Those who are interested in enrolling in the clinical trial must be 18-80 years old and have high blood pressure that has not responded to medication. Two-thirds of the participants will be randomized into the treatment group, and the remaining third into a control group. The treatment group will receive the renal denervation procedure, while the control group will go through a similar procedure without receiving the actual denervation. After six months of monitoring, patients will be told whether they were in the treatment or control group, and patients in the control group will be given the opportunity to undergo the renal denervation procedure at that time.
Jessica Shugart is a science-writing intern for the medical school's Office of Communication & Public Affairs.
Stanford Medicine integrates research, medical education and health care at its three institutions - Stanford School of Medicine, Stanford Health Care, and Stanford Children's Health. For more information, please visit the Office of Communications website at http://mednews.stanford.edu.