FLOWER-MI: FFR-Guided Complete Revascularization Shows No Advantage in STEMI

Ted Bosworth

May 16, 2021

For patients with ST-elevated myocardial infarction (STEMI) undergoing complete revascularization, percutaneous coronary interventions (PCI) guided by fractional flow reserve (FFR) relative to angiography-guided PCI do not result in significantly lower risk of death or events, according to data from the randomized FLOWER-MI trial.

Rather, the events at 1 year were numerically lower among those randomized to the angiography-guided approach, according to the principal investigator of the trial, Etienne Puymirat, MD, PhD.

Prior studies showing an advantage for FFR-guided PCI in patients with coronary syndromes provided the hypothesis that FFR-guided PCI would also be superior for guiding PCI in STEMI patients. In the multicenter FAME trial, for example, FFR-guided PCI for patients with multivessel disease was associated with fewer stent placements (P < .001) and a nearly 30% lower rate of events at 1 year (P = .02).

While the advantage of complete revascularization, meaning PCI treatment of nonculprit as well as culprit lesions, has already been shown to be a better strategy than treatment of culprit lesions alone, FLOWER-MI is the first large study to compare FFR to angiography for guiding this approach to STEMI patients with multivessel disease, said Dr. Puymirat of Hôpital Européen George Pompidou, Paris, at the annual scientific sessions of the American College of Cardiology.

In this trial, involving multiple centers in France, STEMI patients were eligible for randomization if they had successful PCI of a culprit lesion and 50% or greater stenosis in at least one additional nonculprit lesion. The complete revascularization, whether patients were randomized to PCI guided by angiography or FFR, was performed during the index hospital admission. Patient management and follow-up was otherwise the same.

After a small number of exclusions, the intention-to-treat populations were 577 patients in the angiography-guided group and 586 in the FFR-guided group. The characteristics of the groups were well matched with an average age of about 62 years and similar rates of risk factors, such as hypertension and diabetes.

Angiography Guidance Just as Good

The primary outcome was a composite of all-cause mortality, nonfatal MI, and unplanned revascularization. By hazard ratio, the risk of having one of these events within 1 year of PCI was numerically greater, at 32 in the FFR-guided group and 24 in the angiography-guided group, but the difference was not statistically significant (1.32; P = .31).

However, the total rate of events was low (5.5% vs. 4.2% for the angiography-guided and FFR-guided groups, respectively) and the confidence intervals were wide (95% CI, 0.78-2.23). This was also true of the components of the primary outcome.

No signal for a difference between strategies could be derived from these components, which included a higher rate of MI in the FFR-guided group (3.1% vs. 1.7%) but a lower rate of death (1.5% vs. 1.7%).

Unplanned hospitalizations leading to revascularization rates were also low (1.9% and 2.6% for angiography-guided and FFR-guided PCI, respectively), although it was reported that the rate of revascularization for nonculprit lesions was about twice as high in the FFR group (53.3% vs. 27.3%).

At 1 year, there were also low rates and no significant differences in a list of secondary outcomes that included hospitalization for recurrent ischemia or heart failure, stent thrombosis, and revascularization. As within the primary composite outcome, no pattern could be seen in the secondary events, some of which were numerically more common in the FFR-guided group and some numerically lower.

In a cost-efficacy analysis, the median per-patient cost of the FFR-guided strategy was about 500 Euros ($607) greater (8,832 vs. 8,322; P < .01), leading Dr. Puymirat to conclude that “the use of FFR for nonculprit lesions appears to be less effective but more expensive,” at least by costs derived in France.

Lack of Statistical Power Limits Interpretation

The conclusion of FLOWER-MI is that FFR-guided PCI in complete revascularization of nonculprit lesions in STEMI patients is not superior to an angiography-guided approach, but Dr. Puymirat cautioned that the low number of events precludes a definitive message.

William Fearon, MD, professor of cardiovascular medicine at Stanford (Calif.) University Medical Center, agreed. Based on his calculations, the trial was substantially underpowered. Evaluating the details of treatment in the FFR group, Dr. Fearon pointed out that a nonculprit lesion with a FFR of 0.80 or less was identified in about 55% of patients. Ultimately, 66% in the FFR group received PCI, eliminating the key distinction between strategies for the majority of patients enrolled.

“Only about one-third of the FFR-guided patients, or about 200 patients, did not receive nonculprit PCI, and therefore only in this small group could we expect a difference in outcomes from the angio-guided group,” Dr. Fearon said.

In response, Dr. Puymirat acknowledged that the rate of events for this trial, which was designed in 2015, were lower than expected. In recalculating the power needed based on the rate of events observed in FLOWER-MI, he estimated that about 8,000 patients would have been needed to show a meaningful difference in these PCI strategies.

Dr. Puymirat reports financial relationships with more than a dozen pharmaceutical companies, including Abbott, which provided some of the funding for this trial. Dr. Fearon reports financial relationships with Abbott, CathWorks, HeartFlow, and Medtronic.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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