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.
Fewer stents were placed in the FFR-guided than angiography-guided group (1.01 vs. 1.5), but Dr. Fearon suggested that it would be very difficult to show a difference in risk of events in a study of this size when event rates at 1 year reached only about 5%.
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.