However, when such treatment is deferred because of a borderline FFR result, patients are far more likely to eventually need a coronary procedure than if the FFR result is clearly normal, according to a study presented today at the SCAI 2013 Scientific Sessions.
“We found that patients with borderline lesions are at higher risk for revascularization,” said Jayendrakumar Patel, M.D., an internal medicine resident at Washington University in St. Louis. “This may represent a group that needs closer follow-up, more intense medical management and healthy lifestyle changes.”
FFR is performed during coronary angiography, but the two tests provide different information. Angiography shows the location and degree of blockage in the coronary arteries. FFR assesses functional impact—that is, whether a particular blockage is responsible for depriving the heart muscle of oxygen-rich blood, a condition known as ischemia. FFR is particularly important in clarifying the functional impact of lesions that are intermediate in severity.
“Fractional flow reserve has truly changed the way we approach and treat coronary artery disease in the catheterization laboratory,” said Jeremiah P. Depta, M.D., a cardiology fellow atWashingtonUniversity. “A single patient can have multiple blockages and, importantly, not all blockages seen on angiography interfere with flow and cause symptoms. Ideally, we would fix only those blockages that definitely contribute to symptoms.”
To assess FFR, an interventional cardiologist threads a small wire with a pressure sensor into a coronary artery, carefully guiding it past the obstruction. Then a medication (usually adenosine) is injected, causing the arteries to open as wide as possible. The arterial pressure in front of the blockage is then compared to the pressure just beyond the blockage. The ratio of these two pressures is used to calculate the FFR. Readings of less than 0.75 identify blockages that are likely to be causing ischemic symptoms, while an FFR reading of more than 0.80 is 90 percent accurate for excluding such blockages. Values in between 0.75 and 0.80 fall into a “gray zone,” but often prompt interventional cardiologists to go ahead with stenting or refer the patient for bypass surgery.
For the study, researchers reviewed the medical records of 720 patients with 881 intermediate-severity coronary blockages. Treatment of the blockages was deferred in all cases because of an FFR test result of 0.75 or greater. Patients were divided into three groups. Group 1 comprised 61 patients with “gray zone” FFR values of 0.75 to 0.80. Group 2 consisted of 254 patients with “borderline normal” FFR values (0.81 to 0.85), and Group 3 consisted of 405 patients with clearly normal FFR values (above 0.85).
During a follow-up that averaged 4.5 years, 18 percent of blockages eventually required treatment with stenting or bypass surgery to restore blood flow to the heart and relieve symptoms. No significant difference in the chances of delayed treatment was observed between Groups 1 and 2. When Group 2 patients with borderline FFR values were compared with Group 3 patients with normal FFR values, researchers found a 72 percent increase in the chances of deferred intervention (p = 0.001).
“This is truly an exciting aspect of our study,” said Dr. Patel. “Not all deferred lesions are created equal. Borderline lesions that are close to the FFR cut-off may have a higher risk for cardiac events, including a higher rate of revascularization.”
Ongoing research will likely offer additional insight, Dr. Depta said. “It would be premature to conclude that the FFR cut-off needs to be revised or that a borderline lesion needs stenting or bypass surgery,” he said. “Our study is a first step. We are currently investigating other patient and lesion characteristics that may alter the risk for revascularization and adverse events after treatment is deferred on the basis of FFR.”
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