Marie Johnson

Marie Johnson’s electronic stethoscope captured evidence of the arterial blockages that took her husband’s life at 43. The CADence device she patented got approval from the U.S. FDA to bring to market. (Russell Barnes/MPR News file photo)

NORTHFIELD — A Northfield, Minnesota, firm is developing technology that might have kept the founder from becoming a young widow.

In 2002, Marie Johnson was working on her doctorate in biomedical engineering at the University of Minnesota. With funding from 3M, she was attempting to develop a computerized stethoscope that would automatically interpret readings for physicians.

Johnson used her 43-year-old husband as a test subject. He had borderline high cholesterol but no signs of heart disease. He swam three times week and had passed a treadmill stress test.

“Nine months later he had a heart attack,” she said. “A complete surprise.”

Johnson suspected her electronic stethoscope had captured evidence of the arterial blockages that killed her husband.

“I remember the night I found the signature, the frequency signature associated with coronary disease,” she said. “And I heard a voice that said, ‘There it is.’”

Johnson said the frequency signature linked to heart disease is caused by turbulence in the artery, as the blood flows around obstructions. The flow through a healthy blood vessel has little to no turbulence.

Years after she identified the acoustic signature, Johnson formed a company, Aum Cardiovascular, to develop a product, helped by a $250,000 federal grant. She’s since persuaded private investors to put $10 million into her company.

The result is a device that looks like a wireless computer mouse. It’s already been approved for sale and use in Europe. It’s called CADence and is equipped with high-fidelity sensors that capture detailed acoustic signals when placed on a patient’s chest. Sophisticated software scans the frequency data for signs of blockages that could cause a heart attack.

“So, if you have chest pain and multiple risk factors, this test is for you,” Johnson said.

She’s heard that only one new device in 10 gets to market. But she’s convinced she’s got a winner.

“To be honest, I think it’s a no-brainer. If you take a look at what’s existing and compare it to what we’ve got, it’s really straightforward in terms of its success,” Johnson said.

Tests with CADence will cost a few hundred dollars and take about 20 minutes to produce readings and assess a patient’s condition.

That’s generally much cheaper and less involved than current diagnostic technology. Clinical trials of the device involving about 1,000 patients are underway in hopes of showing it’s at least as good as a complicated stress test often used now.

The clinical trials, paperwork and other demands of getting a new medical device approved are long, expensive and maddeningly complicated. But consultant David Furr said the FDA’s process is fundamentally aimed at two concerns.

“Safety and effectiveness — It’s not going to hurt somebody, and that it does what it is intended to do and gives the outcomes it’s intended to give. For this type of device the real proof is going to be in the clinic outcomes and clinical study,” Furr said.

Morningstar analyst Debbie Wang said Aum Cardiovascular’s clinical trials will go a long way toward deciding the market and commercial viability of the product. They could also help determine whether a big industry player is likely to buy Johnson’s company to take ownership of its innovations.

“Many, many med tech companies get taken out in the developmental stage, especially if there’s real potential behind that technology,” Wang said.

Aum’s electronic stethoscope has attracted some impressive talent to the company, including Medtronic’s former chief regulatory officer, Dr. Susan Alpert.

But for Marie Johnson, this is a personal quest. After her husband died, she took the autopsy report to the cardiologist who was her faculty adviser. He said the findings indicated her husband died from a blockage in what’s grimly known as the widow-maker artery.

“I asked him, ‘If you had known it was there, could you have done anything to fix it?’” she recalled. “And he said, ‘Yes.’”

Results of the clinical trials are expected early next year. The FDA may decide whether to approve CADence for sale in the United States by 2017.

Minnesota Public Radio News can be heard in Owatonna on 103.9 FM or online at

Jeffrey Jackson is the managing editor of the Owatonna People's Press. He can be reached at 507-444-2371 or via email at

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