WASHINGTON – Nothing doctors prescribed controlled Michael Garrity’s dangerously high blood pressure — until they zapped away some nerves on his kidneys.

If that sounds weird, well, kidneys help regulate blood pressure in part through signals from certain nerves. The new treatment disrupts overactive renal nerves.

“My blood pressure would spike and I’d run out of breath and feel tired, and that doesn’t happen anymore,” said Garrity, 62, of Needham, Massachusetts. He still takes medicine but at lower doses, his blood pressure normal for the first time in years. “I’m thrilled.”

About half of U.S. adults have high blood pressure, a major risk for heart attacks, strokes, kidney failure, even dementia. Many people don’t even realize they have hypertension until it’s done serious damage.

“Know your blood pressure, know the numbers,” stressed Dr. Randy Zusman of Massachusetts General Hospital, who specializes in the hardest-to-treat cases and advises people who think they’re fine to at least get a yearly check.

And only a fraction of patients have their hypertension well-controlled, meaning there’s a need for novel strategies. The Food and Drug Administration approved that “renal denervation” option about a year ago, based on studies showing a modest benefit in patients whose blood pressure remains high despite multiple medicines.

Now, after the American Heart Association recently deemed it promising, some hospitals including Mass General Brigham are cautiously offering it as they work out who are good candidates — and whether their insurance will cover a minimally invasive procedure costing thousands of dollars.

What is high blood pressure?

Two numbers describe blood pressure. The top, “systolic” pressure, is the force blood puts on the walls of arteries as its pumped out of the heart. The bottom “diastolic” number measures that same pressure but between heartbeats.

Normal is less than 120 over 80. Blood pressure naturally fluctuates throughout the day, higher when you’re physically active or stressed. But when it stays high — consistently 130 over 80 or higher, according to the most recent guidelines — it stiffens arteries and makes the heart work harder.

How to measure blood pressure

It doesn’t take a doctor’s visit. Pharmacies and sometimes even libraries offer screening, and people can use at-home monitors.

To avoid falsely high readings, the American Medical Association has tips: Sit quietly with feet on the floor, legs not crossed. Place the cuff on a bare arm, not over clothing. Don’t dangle the arm — rest it on a table.

Drugs aren’t the only way to treat high blood pressure

Lifestyle changes are the first step, especially for otherwise healthy people. Guidelines urge losing weight, exercise, eating more fruits and vegetables, limiting salt and alcohol, and taking steps to handle stress.

Medicine is a must once hypertension reaches 140 over 90. The average patient requires two or three drugs, sometimes more, along with healthier living, Zusman said.

But the hypertension Garrity has struggled with since his late 20s is treatment-resistant. Despite taking four to six drugs plus a strict diet and exercise, his blood pressure regularly reached 150 over 100 or worse.

What is renal denervation?

Doctors thread a small catheter, or tube, through blood vessels to reach the kidneys, and then beam in ultrasound or radiofrequency energy. Those pulses pass through the renal arteries to selectively target surrounding nerves, said Dr. Joseph Garasic, a Mass General interventional cardiologist who performed Garrity’s procedure. It takes about an hour.

Although already used in other countries, a key U.S. trial of renal denervation failed about a decade ago, prompting changes before researchers tried again. In November 2023, the FDA approved two catheter systems, from Recor Medical and Medtronic.

It’s not a cure – and some patients get no benefit. But Garasic said multiple studies show on average an 8 to 10-point drop in blood pressure, a modest but important improvement. Some like Garrity see a bigger drop, enough to gradually scale back medications.

The FDA deemed the procedure safe for carefully chosen patients — it wasn’t tested in those with kidney disease or narrowed arteries, for example. And studies have lasted only a few years, not long enough to tell if the nerves might eventually regenerate.

Guidance from the American Heart Association urges would-be patients and experienced doctors to have “thoughtful and informed discussions” to decide who’s a good candidate.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.