A California supercomputer is advising heart specialists in Minneapolis on when they should — and more importantly when they shouldn’t — thread instruments inside patients’ blood vessels to examine blockages.

The so-called HeartFlow system uses images from a patient’s CT scan and analyzes them against volumes of data on the human vascular system and the science of fluid dynamics. As a result, it can diagnose patients’ needs — and help doctors avert heart attacks and stroke — without the costly and invasive procedure of inserting a catheter.

“It should decrease the number of people who end up in the cath lab who don’t have lesions that matter,” said Dr. John Lesser, who directs cardiovascular imaging at Allina Health’s Minneapolis Heart Institute.

Allina is the first in Minnesota to use HeartFlow — and currently bears the cost of the analysis for patients because cardiologists there believe it will prove its worth in a field prone to excessive testing and procedures.

CT or X-ray images of a patient’s heart and blood vessels, also called coronary angiograms, detect the locations and shapes of blockages and plaque formations inside blood vessels. But they don’t distinguish those that need fixing from those that can be left alone or treated with medications — unless doctors also thread catheters inside patients to see if the blockages are cutting off blood flow.

Trouble is, catheterization is expensive and carries at least slight risk of strokes and other complications. And it’s often unnecessary when blood flow turns out to be adequate.

“Sometimes, a blocked artery causes symptoms when we do not believe it will,” Lesser said. “More often, a blocked artery looks like a problem but does not cause symptoms.”

A 2014 review of coronary angiograms in New York, for example, found one-third were clearly needed, and one-fourth were inappropriate.

HeartFlow’s computer analysis provides estimates of blood flow in clogged arteries that rival test results from catheterization. The system received approval from the U.S. Food and Drug Administration last year following clinical trials — including one released last August that showed a 61 percent reduction in invasive coronary tests, with no change in complications or treatments.

One of Lesser’s first HeartFlow patients was 77-year-old Colleen Loye of Isanti, who suffered heart attacks in 2004 and 2013 and recently noticed her breathing was labored.

A CT scan showed plaque formations clogging up some of her blood vessels. But after the results were fed through HeartFlow’s supercomputer in California, they showed that her blood flow was above the threshold that is problematic.

Ruling out cardiac changes as a cause of her breathing problems allowed Loye’s doctors to focus on her lung condition — which stemmed from a lifetime of smoking and a long career replacing the upholstery of vintage cars.

“Back in those years, they didn’t have the safety standards they do today,” said Loye. “There was a lot of chemical paint, chemical glue — and the smoking of course didn’t help either. I wasn’t smart enough to quit. My husband quit at age 50 cold turkey.”

Without HeartFlow, Lesser said, Loye would have needed a catheterization procedure to rule out cardiac problems.

Wasteful procedures?

Excessive invasive testing has led to another problem: Once they are already noodling inside a patient’s blood vessels, some doctors are more inclined to proceed with placing stents or making other repairs. And while stents are lifesaving when they prop open blockages that are squeezing off blood flow, the mesh devices can cause scarring and new blockages.

Estimating that 9 percent to 20 percent of all stent placements are unnecessary, doctors in Wisconsin and Florida last year started testing a SMARTcare guidance system to help colleagues make decisions and reduce inappropriate stent usage.

Avoiding cardiac cath procedures also can save money, Lesser said. The invasive procedure costs $5,000, whereas a CT scan costs only about $700 and computer analysis of the results costs another $1,500 or so. Whether HeartFlow saves money for the health care system long-term depends on how often it’s used, and whether doctors use it in place of invasive tests and not just in addition to them.

Loye said she appreciated the less invasive approach. She wasn’t conscious during her first catheterization to treat a heart attack, but she remembers the discomfort of the second one.

“If a person can avoid an invasive test like that,” she said, “to me, it’s a better way to have it done.”