FFR guided revascularization no better than angiographic guidance in STEMI patients, FLOWER MI study

Recent trials like COMPLETE have shown that complete revascularisation should be the norm in acute STEMI setting unless complicated by hemodynamic instability. However, whether complete revascularization should be guided by fractional flow reserve (FFR) or angiography-alone unclear. Puymirat et al in the results of FLOWER-MI study published this week in NEJM have shown that an FFR-guided strategy did not have a significant benefit over an angiography-guided strategy with respect to the risk of death, myocardial infarction, or urgent revascularization at 1 year.

In patients with chronic coronary syndrome or acute coronary syndrome without ST-segment elevation, the use of fractional flow reserve (FFR) measurement during percutaneous coronary intervention (PCI) to assess the functional severity of coronary lesions results in a lower risk of major cardiovascular events than myocardial revascularization guided by angiography.

But it is unclear whether an FFR-guided approach results in better clinical outcomes than an angiography-guided approach for complete revascularization in patients with STEMI and multivessel disease.

To find answers to this question, FLOWER MI investigators conducted a multicenter trial, and randomly assigned patients with STEMI and MVD who had undergone successful PCI of the infarct-related artery to receive complete revascularization guided by either FFR or angiography.

The primary outcome was a composite of death from any cause, nonfatal myocardial infarction, or unplanned hospitalization leading to urgent revascularization at 1 year.

Researchers found that an FFR-guided strategy for complete revascularization was not superior to an angiography-guided strategy for reducing the risk of the composite primary outcome (death from any cause, nonfatal myocardial infarction, or unplanned hospitalization leading to urgent revascularization at 1 year). The individual components of the primary outcome, as well as all other clinical outcomes, did not differ significantly between the two groups.

During follow-up, a primary outcome event occurred in 32 of 586 patients (5.5%) in the FFR-guided group and in 24 of 577 patients (4.2%) in the angiography-guided group (hazard ratio, 1.32; 95% confidence interval, 0.78 to 2.23; P=0.31). Death occurred in 9 patients (1.5%) in the FFR-guided group and in 10 (1.7%) in the angiography-guided group; nonfatal myocardial infarction in 18 (3.1%) and 10 (1.7%), respectively; and unplanned hospitalization leading to urgent revascularization in 15 (2.6%) and 11 (1.9%), respectively.

In the Fractional Flow Reserve versus Angiography for Multivessel Evaluation (FAME) trial, routine measurement of FFR during PCI in patients with stable multivessel disease resulted in a lower incidence of major adverse events than angiography-guided PCI at 1 year.

The discrepancy of results such previous studies supporting the use of FFR may be due to the fact that performing FFR measurement at the time of index PCI of the infarct-related artery may be unrealistic under routine clinical conditions. As a result, more than 95% angioplasties of non-infarct related arteries were performed as a staged procedure (done within 5 days). The mean time delay between the interventions was 2.6±1.4 days in the FFR-guided group and 2.7±3.3 days in the angiography-guided group. Staged procedures expose the patient to a second procedure with its associated risks and this could have led to increased event rates.

The performance of FFR during the initial procedure, which would result in fewer additional procedures, could save exposure to radiation and contrast materials. However, prolonging the index procedure could lead to a higher risk during a period of acute vulnerability (active prothrombotic state, acute inflammation, and risks of hemodynamic instability and arrhythmia) than repeating the procedure 48 hours later when the patient's condition is more stable. Also, assessment of nonculprit lesions may be uncertain during the acute event, when vasospasm may lead to an overestimate of stenosis severity.

Summarizing the  results, FLOWER MI study showed that in patients with STEMI undergoing complete revascularization, an FFR-guided strategy did not have a significant benefit over an angiography-guided strategy with respect to the risk of death, myocardial infarction, or urgent revascularization at 1 year.

"However, given the wide confidence intervals for the estimate of effect, the findings do not allow for a conclusive interpretation", noted the authors in conclusion.

Source: NEJM: May 16, 2021DOI: 10.1056/NEJMoa2104650