Diagnostics & Imaging Week

By using a new method of measuring blood flow to the heart, cardiologists may be able to refine the coronary stenting procedure in a way that would lead to fewer artery-opening stents being used – and ultimately better patient outcomes and reduced hospital costs.

This is the take-home message from a study published in the Jan. 15 issue of New England Journal of Medicine that evaluated the benefits of a new diagnostic tool to measure blood flow and determine whether stenting was the best option.

"Not only were the outcomes better, the cost was less," said William Fearon, MD, co-principal investigator of the multi-center international study called FAME (Fractional flow reserve vs. Angiography in Multivessel Evaluation) and assistant professor of cardiovascular medicine at the Stanford University School of Medicine (Stanford, California). "Now there's scientific support for cardiologists to apply this new technique."

Fearon told Diagnostics & Imaging Week that more and more patients are presenting with multiple narrowings in their coronary arteries and that it is not always clear which arteries are contributing to the problem. He also said that coronary angiograms are not always definitive and can actually be misleading. Thus, the study suggests that doctors should go one step beyond the traditional method of relying solely on the angiogram to determine which arteries should be stented for patients with multivessel coronary artery disease.

By using a method called fractional flow reserve (FFR), which involves inserting a coronary pressure guidewire into the artery, doctors can measure whether blood flow is actually reduced to a dangerous level beyond any apparent narrowing. In some cases, medication may be a better option to stenting, the study suggests.

The study started enrolling patients in January 2006 and included about 1,000 patients. Half the patients were assigned to the traditional method of determining which arteries should be stented (angiogram and other clinical data).

The other half were randomized to having an angiogram and the additional FFR measurement using a pressure sensor mounted on a guidewire, PressureWire Certus, developed by Radi Medical Systems (Uppsala, Sweden), which was acquired in December by St. Jude Medical (St. Paul, Minnesota). Radi funded the FAME study.

With an angiogram, a catheter is used to inject dye into the arteries, then X-rays are taken which doctors examine looking for narrowed arteries. Any arteries that look significantly narrowed are then propped open with a stent. To measure blood flow beyond the areas in the arteries that appear narrowed, the pressure wire was threaded through the same catheter used for the angiogram.

"The pressure wire is a thin wire with a sensor near the tip that can measure the pressure of blood flow," Fearon said. "If the narrowing is truly significant it will cause a drop in blood pressure beyond the narrowing. If the pressure was 80% or less than the pressure in front of the narrowing (an FFR value of .80 or less), a stent was implanted."

Researchers found that patients who received the additional blood flow test received one-third fewer stents than the group examined only with an angiogram. The angiogram-only patients received 2.7 stents on average. The FFR patients received only 1.9 stents on average.

After one year, follow-up statistics showed that within the traditional group, 18.4% of the patients had died, suffered a heart attack or needed a bypass surgery or repeat stent procedure, compared with 13.2% among those who received the additional pressure wire test.

St. Jude noted that in the study, the risk of a patient dying or having a heart attack was reduced by about 35% when FFR measurement was performed (11.1% for the angiography-guided group compared to 7.3% for the FFR-guided group).

Nico Pijls, MD, PhD, professor of cardiology at Catharina Hospital (Eindhoven, the Netherlands), was the other co-principal investigator. Fumiaki Ikeno, MD, a research fellow at Stanford, is a co-author of this study.

"Treatment decisions today should not be just about which stent you pick, they should be about where you put a stent," Pijls said. "We know that stenting ischemia-producing stenoses improves symptoms and outcomes, and that stenting non-ischemic stenoses has no benefit compared to medical treatment only. FFR is a simple measurement that can be performed quickly in the cath lab and makes it possible to treat culprit lesions only, while avoiding time, damage, and expense from placing stents which do not benefit the patient."

Anders Qvarnström, formerly COO of Radi, now part of the St. Jude Medical Cardiovascular Division, told D&IW that the wire used in the FAME study is the company's seventh generation of a product, counting the early optical wires Radi developed.

"It is very easy to set up as the study proves, the wire handles more or less like a standard guidewire," Qvarnström said.

Patients included in the study either suffered from chest pains or were recovering from mild heart attacks. All patients had multiple coronary arteries with narrowings.

"We weren't really trying to say that stenting is bad or that there is too much stenting going on," Fearon said. "We were trying to show that there is a way of refining the procedure."

He told D&IW that he believes this study will have an immediate impact on how cardiologists determine which arteries should be stented in patients with multiple narrowing arteries.

Fearon said the FFR procedure did not require any extra procedural time and resulted in decreased medical costs. "Each stent on average costs roughly $2,000," he said. "The pressure wire test runs an additional $700."

St. Jude noted that the average procedural costs were $5,332 for the FFR-guided group compared to $6,007 for the angiography-guided group. It took an average of 71 minutes to complete PCI in the FFR-guided group compared to 70 minutes in the angiography-guided group.

"The take-home message is that the wire is able to give you more information about whether a coronary narrowing is truly causing abnormal blood flow to the heart," Fearon said. "Some narrowings that might look bad would respond just as well to medication, while others that appear innocent may benefit from stenting. By measuring FFR, one is better able to make this distinction and improve the patient's outcome, while also saving healthcare dollars."

The FAME study included about 1,000 patients in the U.S. and Europe. Twenty hospitals participated in the study, six from the U.S. including 115 patients from Stanford University Medical Center and the Veterans Affairs Palo Alto Health Care System.

St. Jude said the study is the first large-scale, randomized, prospective, multi-center clinical trial that compares stenting guided by FFR to stenting guided by angiography alone in patients with two or more diseased coronary arteries. The goal of the FAME study is to explore whether routine use of FFR can guide physicians to place stents optimally when assessing patients with multivessel disease, the company said.

PressureWire Certus has regulatory approval in Europe and Japan as well as FDA clearance.