Published in UAB Insight, Summer 2008
Early Results of Implantable System Are Promising
Resistant hypertension affects up to 30% of the 72 million Americans with high blood pressure. Compared with people with adequately controlled blood pressure, individuals with resistant hypertension are at higher risk for stroke, myocardial infarction, congestive heart failure, and renal failure. Management of these patients, who often have multiple comorbid conditions, is challenging.
A new implantable device that mimics function of the body's baroreceptors may prove an effective option for improved blood pressure control in some individuals with drug-refractory hypertension, says UAB vascular surgeon Marc A. Passman, MD, principal investigator for the UAB site of a pivotal trial of the CVRx Rheos Baroreflex Hypertension Therapy System (CVRx Inc, Minneapolis, Minnesota).
A pulse generator placed under the collarbone connects to two thin lead wires implanted in the left and right carotid arteries. The system electrically activates the carotid baroreflex, sending neural signals indicating an excessive rise in blood pressure to the central nervous system (CNS). The CNS sends neural signals to counteract this perceived rise through several mechanisms, including dilating blood vessels, reducing heart rate, and promoting fluid excretion by the kidneys.
Results of European and US feasibility trials are promising, according to abstracts presented at a March 2007 American College of Cardiology meeting. After 6 months of treatment, the Rheos system reduced systolic blood pressure (SBP) by an average of 22 mm Hg (166 vs 187) and diastolic blood pressure by an average of 16 mm Hg (96 vs 112). Patients, all of whom had stage 2 hypertension despite taking ≥3 medications, have maintained reductions for more than a year. The devices have been well-tolerated with no unexpected serious adverse events.
The pivotal trial will enroll more than 300 patients at 50 US centers. Passman has now implanted the first baroreflex device in Alabama. "Our first patient was a relatively young individual who has a long history of labile blood pressure despite taking five medications," he says. "Her initial reduction in blood pressure was impressive and her lability has diminished."
Candidates for the randomized trial are those with SBP ≥160 mm Hg despite treatment with ≥3 antihypertensives, including a diuretic. Surgeons implant the device in all participants. All patients have their device turned off for the first month and then are randomized to device "on" or "off" for 6 months. After 6 months, all patients receive active therapy.
"Medications and lifestyle modifications control blood pressure in most people," Passman says, "but a select group does not respond well to drugs. If this system proves safe and effective, it will be an important option for those patients."
"Resistant hypertension is a common clinical problem that, unfortunately, we can anticipate becoming even more common as the population ages. Effective treatment strategies are definitely needed," says David A. Calhoun, MD, study coinvestigator and medical director of UAB's Vascular Biology and Hypertension Program. "Novel treatment approaches such as the Rheos system offer a potentially enhanced benefit for patients with this difficult problem. Preliminary results for the device are encouraging and warrant larger testing, as is being done by UAB and other centers."
FOR MORE INFORMATION:
Dr. Marc Passman
Dr. David Calhoun
1.800.UAB.MIST
mist@uabmc.edu