By Jeffrey Zimmet, MD, PhD
SOURCE: Depta JP, et al. Risk model for estimating the 1-year risk of deferred lesion intervention following deferred revascularization after fractional flow reserve assessment. Eur Heart J 2014 Oct 21. pii: ehu412. [Epub ahead of print].
Fractional flow reserve (FFR) is an invasive technique for determination of the physiologic significance of an intermediate coronary lesion. Multiple studies have demonstrated the ability of FFR to guide revascularization decisions. For the most part, a negative FFR predicts the ability to safely defer interventional treatment of an intermediate lesion, with a relatively low risk of downstream events. The commonly used cutoff values of 0.75 and 0.80, although derived rather inelegantly thorough comparisons with non-invasive stress testing, have been validated empirically and overall performed well in clinical studies. However, not all lesions assessed as "negative" by FFR will remain quiescent. Among lesions for which intervention was deferred based on FFR, rates of future revascularization have ranged from 2.5-11% in the first year. The determinants of such delayed lesion intervention (DLI) have not been described previously.
Depta and colleagues from the Washington University School of Medicine retrospectively analyzed 720 patients with 881 intermediate-severity coronary stenoses who had a percutaneous coronary intervention (PCI) deferred based on FFR results performed between 2002 and 2010. Unlike some prior studies, which primarily looked at patients in the stable setting, approximately one-half of the subjects in this study underwent FFR assessment during an acute coronary syndrome (ACS), of which a majority were unstable angina (39%) and a lesser fraction were acute myocardial infarction (MI) (12%). The mean FFR value among deferred lesions was 0.85, and only 7% of deferred lesions had FFR values below the FAME study-inspired cutoff of 0.80.
After the index procedure, 5% of all PCI-deferred lesions underwent subsequent revascularization in the first year, while 18% (n = 155) underwent deferred lesion intervention (DLI) (74% by PCI and 26% via coronary artery bypass grafting) during a mean follow up of 4 years. Of the DLI lesions, 65% were treated in the ACS setting, while the remaining 35% were treated primarily for stable angina. Within the study population, 79 acute MIs occurred during the study period; the culprit lesion was identified as the lesion that had previously been deferred based on the index FFR in 38% of the acute MIs (n = 30).
A prediction model for DLI was developed using stepwise Cox regression. In the final model, multivariable predictors of DLI at 1 year included lower FFR value, younger age, current or former smoking, history of coronary artery disease (CAD) or prior PCI, multi-vessel CAD, and increased serum creatinine. The predicted risk of DLI at 1 year in the cohort varied from 1%-40%. The authors concluded that "Knowledge of a patient's risk for future revascularization of a lesion deferred based on FFR may provide clinicians and patients with useful information when considering potential strategies to prevent later adverse events leading to revascularization."
COMMENTARY
We all like simple tools to aid in clinical decision-making. FFR has grown in use based in large part on a purely binary treatment algorithm: Intervene on lesions with values below a certain cutoff and defer those with values above. This study drives home an important point that although a lesion has been assessed as non-significant by FFR, there is considerable risk that the same lesion may require revascularization at a later point in time. At 1 year in this real-world study, 1 in 20 initially deferred lesions had been revascularized, while at 4 years this approached 1 in 5. Keep in mind that there may very well be a different rate of DLI among patients referred for elective cardiac catheterization vs those presenting with ACS.
Of all the variables that fell out of the prediction model, it is the FFR value itself that is likely the most significant, if not also the most obvious. It should be unsurprising that a lesion for which PCI was deferred based on an FFR value barely above the cutoff, at 0.81 for example, would have a higher risk of requiring future intervention compared with a lesion with a much higher FFR value of 0.95.
Can such a prediction model actually inform medical practice? We all strive to prescribe optimal medical therapy to every patient with confirmed coronary atherosclerosis. The idea that some ill-defined additional preventive measures could be directed specifically toward those higher-risk patients with FFR-deferred lesions is likely not very realistic. Nonetheless, closer follow up, as well as maintaining a high index of suspicion for worsening symptoms or changing clinical conditions in these patients, could ultimately prove to be beneficial.
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