NATIONAL HARBOR, MD. – Of characteristics that might predict which patients with resistant hypertension will respond to carotid body ablation, the relative activity of the carotid body organ itself might be critical for moving this technology forward, an investigator on a first-in-man study suggests.
The study, first presented in 2018 at the European Society of Cardiology congress, showed carotid body ablation resulted in significant but modest reductions in blood pressure in patients with resistant hypertension.
Ted Bosworth/MDedge News
Dr. Felix Mahmoud
For many reasons, the carotid body is an attractive target for sustained or indefinite control of resistant hypertension, but median systolic blood pressure reductions following ultrasound ablation were highly variable in the first-in-man study, according to Felix Mahfoud, MD, of Saarland University Hospital in Homburg, Germany, a coinvestigator on the study who discussed the findings at CRT 2020 sponsored by MedStar Heart & Vascular Institute.
Of several strategies being pursued to separate those most likely to gain a major benefit, simply measuring carotid body activity is now emerging as particularly promising.
“Patients with a high degree of carotid body activity had a significantly larger fall in blood pressure versus all other methods of grouping patients,” Dr. Mahfoud reported.
The carotid body is a “grain-size” organ of about 2 mm in size that sits on the carotid bifurcation. It communicates directly with the brain to alter sympathetic activity in response to changing levels of such physiologic variable as oxygen, carbon dioxide, and pH, according to Dr. Mahfoud.
In a 2016 proof-of-principle study conducted in resistant hypertension patients, surgical resection of the carotid body was associated with a median 18–mm Hg reduction in systolic blood pressure (SBP) on 24-hour ambulatory monitoring that was sustained through 24 months (Narkiewicz K et al. JACC Basic Transl Sci. 2016;29:313-24).
Subsequently, ultrasound ablation of the carotid body was by way of a transcatheter approach. Dr. Mahfoud’s unpublished first-in-man study, conducted in 2018 enrolled 38 patients with resistant hypertension. The median reductions from baseline of 7-8 mm Hg at 1, 3, and 6 months were significant (P less than .01), but the benefit was disappointingly modest.
However, the variability was large. Some patients achieved SBP reductions of up to 20 mm Hg at 6 months, prompting additional analyses to understand if the best responders could be identified. When compared to the mean reduction of 7 mm Hg at 6 months, this represented a 13–mm Hg additional reduction. There are now several potential approaches being considered.
In addition to carotid body activity, which is readily measured and has substantial potential to serve as a routine selection criterion, isolated systolic hypertension (ISH) was also found to be a discriminator for response. For those with ISH, which Dr. Mahfoud noted is also characterized as “stiff arteries,” SBP reductions at 6 months were negligible, but in those without ISH, the median reduction from baseline was 11 mm Hg.
Further investigations are now planned to evaluate potential predictors of response, according to Dr. Mahfoud. He believes carotid body ablation might have advantages over alternatives, including other experimental therapies, in at least some patients.
To deliver ultrasound ablation in the first-in-man study, a propriety catheter (Cibiem transvenous system) was advanced through the jugular vein guided with intravascular ultrasound. When the carotid body was reached, two to three ultrasound ablations of 8-12 seconds each were applied. The procedure time was 20-30 minutes.
Initially, an arterial approach to the carotid body was used. However, after a transient ischemic attack early in the series, the approach was switched to the jugular vein. There have been no serious subsequent procedural-related complications since.
Although the median SBP reductions were modest, they were not insignificant in a population selected for severe resistant hypertension. The median SBP at entry was 180 mm Hg in patients taking a median of 4.5 antihypertensive drugs, according to Dr. Mahfoud.
In other words, this approach still retains promise for selected patients if larger studies demonstrate that response can be predicted, and the data continue to support tolerability.
A venous approach to the carotid body with intravascular ultrasound guidance and therapeutic ultrasound appears “to offer a safe and effective treatment option in resistant hypertension,” according to Dr. Mahfoud. “A companion diagnostic test is being developed to determine whether patients are likely to respond to this therapy.”
Dr. Mahfoud reports financial relationships with Medtronic, St. Jude, and ReCor.
This article was updated to clarify the study details and correct misspellings of the presenter's name.
SOURCE: CRT 2020.