Most people who are being treated for hypertension or high blood pressure can recite a list of recommendations and treatments: watch your diet, get more exercise, manage your stress, take medication. Despite their best efforts, however, research suggests that 28 percent of people who are being treated for high blood pressure are considered resistant to treatment. As a result, they have three times the risk of cardiovascular problems such as stroke, heart attack, and heart failure as people whose treatment is successful.
Blood pressure is the force of blood against the walls of the arteries. It is measured as two numbers: the systolic pressure exerted as your heart beats over the diastolic pressure between beats. Normal blood pressure is less than 120 mmHg (millimeters of mercury) systolic and less than 80 mmHg diastolic. Treatment-resistant hypertension is defined as blood pressure that remains greater than 140/90 mmHg in spite of treatment with three or more anti-hypertensive medications. Nearly 6 million Americans fall into this category.
Now, several medical centers across the United States are enrolling patients to participate in a clinical trial of a procedure that controls high blood pressure by regulating the activity of nerves lining the walls of the arteries leading to the kidneys. These nerves are part of the sympathetic nervous system, which helps the body control blood pressure by narrowing blood vessels or directing the heart to pump harder. In people with hypertension, the renal nerves are hyperactive. This leads to increased blood pressure and contributes to heart, kidney and blood vessel damage.
The Symplicity HTN-3 study is a clinical trial of the investigational Symplicity® Renal Denervation System™ for treatment-resistant hypertension. Renal denervation is a minimally invasive, catheter-based procedure that regulates nerve activity. The Symplicity Renal Denervation System consists of a flexible catheter and proprietary generator. While the patient is conscious but sedated, the Symplicity catheter is introduced through a separate catheter placed through the skin into the femoral artery in the upper thigh, and is then threaded up into the renal artery leading to each kidney. It is connected to the Symplicity generator, which produces controlled, low-power radio-frequency (RF) energy.
Once in place within the renal artery, the tip of the Symplicity catheter is placed against the arterial wall in several places where it uses controlled, low-power pulses of RF energy to interrupt the signals from the renal nerves. The treatment does not involve a permanent implant, and it is not known whether the changes to the nerves are permanent. Researchers believe the treatment may reduce the amount of medication patients require, but will not replace the drugs altogether.
The Symplicity HTN-3 study is a randomized controlled trial designed to evaluate the safety and effectiveness of renal denervation with the investigational Symplicity system in patients with treatment-resistant hypertension and systolic blood pressure higher than 160 mmHg. The study will enroll approximately 530 treatment-resistant hypertension patients across several U.S. medical centers, including Scripps Clinic. Researchers will study whether renal denervation, along with ongoing treatment with anti-hypertensive medications, has the potential to help patients with treatment-resistant hypertension achieve their target blood pressure levels.
Patients enrolled in the clinical trial will be randomly assigned to a group, with two out of three assigned to a treatment group that receives the investigational procedure. One out of three will be assigned to the control group that does not receive renal denervation. All patients will continue to take their blood pressure medications throughout the study. The study will measure changes in blood pressure over six months as well as any significant side effects or complications. If they choose, control group participants may receive the renal denervation treatment six months after the study has ended.
Renal denervation has been used since 2007 to treat more than 2,000 patients worldwide, and the treatment has been available in Europe and Australia since 2010. It is not approved by the U.S. Food and Drug Administration (FDA).