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Medtronic, others push forward with HTN renal artery denervation

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Years away from clinical use

We need to see randomized trials. This technology looks encouraging, but there’s nothing definitive yet in terms of direct applicability. The initial proof of concept study suggested it does lower blood pressure – but not by a lot. I think it’s a long way from common clinical use, but it’s reasonable to keep looking at it.

Dr. William Cushman is professor of medicine and physiology at the University of Tennessee Health Science Center, Memphis

Dr. William Cushman

Dr. William Cushman, a professor of medicine and physiology at the University of Tennessee Health Science Center, Memphis, made these comments in an interview. He was an author on the Eighth Joint National Committee hypertension guideline and was not involved in the Medtronic study.



– Hypertensive patients averaged about a 10-mm Hg drop in 24-hour ambulatory systolic blood pressure and about a 12-mm Hg drop in office systolic blood pressure, 2 years after treatment with Medtronic’s new Symplicity Spyral renal artery denervation catheter, according to a review of the company’s renal artery denervation registry.

No major safety issues were reported, but there was no reduction from baseline in the number of antihypertensive drugs that patients were prescribed, which averaged more than four.

Dr. Michael Weber is a Medtronic investigator and a professor of medicine at State University of New York, in Brooklyn,

Dr. Michael Weber

The registry includes 2,237 patients treated with the company’s original denervation device – the Symplicity Flex catheter – and followed for up to 3 years, as well as 278 treated with the Symplicity Spyral and followed for up to 2 years. Europeans make up the bulk of the registry, since the devices are not approved in the United States.

The company withdrew the Flex catheter from development after a large, randomized U.S. trial found no benefit over a sham procedure for resistant hypertension (N Engl J Med. 2014 Apr 10;370[15]:1393-401). “In the future, everything will be built around the Spyral catheter,” said Michael Weber, MD, a Medtronic investigator and a professor of medicine at State University of New York, Brooklyn. He presented the registry findings at the joint scientific sessions of AHA Council on Hypertension, AHA Council on Kidney in Cardiovascular Disease, and American Society of Hypertension.

The Spyral, he said, has two key advantages over the Flex. The Flex had just a single electrode, so operators had to rotate the tip into four quadrants to fully denervate renal arteries, “a tricky business at the best of times and very often not successfully achieved.” Inadequate ablation might have contributed to the trial failure, Dr. Weber said.

The Spyral catheter, on the other hand, has four electrodes placed radially around a spiral catheter, so all four quadrants can be ablated at once, without undue gymnastics. The Spyral can also enter the smaller branches of the main renal arteries, which might allow for more complete denervation, he said.

“We all anticipate better results with the Spyral, but let’s be cautious. We need more data and obviously data from controlled clinical trials. There’s a lot to be learned yet about this whole procedure,” Dr. Weber said.

Medtronic is planning a large trial of its new device following the recent publication of a successful proof-of-concept study that pitted the Spyral in 38 hypertensives against a sham procedure in 42. The Spyral group had a 5 mm Hg greater reduction in systolic ambulatory blood pressure at 3 months, among other findings. To avoid confounding, investigators took patients off their blood pressure medications during the study (Lancet. 2017 Aug 25. pii: S0140-6736(17)32281-X. doi: 10.1016/S0140-6736[17]32281-X).

Other companies are pushing forward with renal artery denervation, as well; Boston Scientific has its own four-quadrant ablation catheter – Vessix – in the pipeline.

In Medtronic’s denervation registry, office systolic blood pressure reductions were a bit larger at 2 years for the older Flex catheter than with the newer Spyral, 15.7 versus 12.0 mm Hg from a baseline of about 170 mm Hg in both groups. Spyral had a slight edge on 24-hour ambulatory systolic blood pressure at 2 years, with an average reduction of 10.4 versus 8.7 mm Hg from a mean baseline of about 155 mm Hg.

For both devices, “when you look at results patient-by-patient, they are dramatically all over the place, including a significant number of patients whose pressures actually increase. I have to assume that it’s patients” who stop taking their medications after the procedure. On the flip side, “I suspect some of our terrific results are because people finally get a touch of religion after the intervention and start taking their drugs for the first time,” Dr. Weber said.

So far, only a handful of Spyral patients have had ablations in renal artery branches. “It seems to have some benefit as judged by office pressure, but the numbers are small, so it’s premature to draw any conclusions,” he said.

Registry patients were in their early 60s, on average, at baseline, and there were more men than women. As with Spyral, Flex patients had no decrease in hypertension prescriptions over time and averaged more than four. “We have not seen many miracle cures in the sense of patients suddenly requiring no drugs at all,” Dr. Weber said.

The procedure seems safe, according to the registry. “There’s nothing to suggest the use of these catheters in the renal arteries causes any sort of acute or later-appearing major renal artery compromise.” With the Flex, less than 1% of patients required renal artery reintervention, which was possibly related to ablation trauma stenosis, “but it’s something to keep on our list of things to look for,” Dr. Weber said.

When asked if the registry fully captures adverse events, Dr. Weber said that “I suspect once [Spyral] goes to market, assuming it does go to market, there will be far more rigorous reporting requirements.”

He reported receiving travel funding, as well as consulting and lecture fees, from Medtronic and Boston Scientific, among other companies.

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