Читать книгу Interventional Cardiology - Группа авторов - Страница 185

A cut‐off FFR value of <0.75 across an epicardial stenosis is accepted to be indicative of myocardial ischemia [1,2]. There is a close correlation between FFR <0.75 and different non‐invasive indices of reversible myocardial ischemia [6,10,11]. Whilst there may be discrepancy with individual functional tests, when multiple tests are performed, agreement is more likely; early work suggests FFR≤0.75 detects 97% of ischemia. Meta‐analytical work suggests the match with non‐invasive testing is typically 70% [10]. The DEFER study demonstrated it was clinically safe to defer revascularization with FFR values over 0.75 [11].

FFR values over 0.80 have over 90% sensitivity of excluding ischemia. The FAME and FAME II studies used a 0.80 threshold, ostensibly to ensure potentially ischemic stenoses were not missed. FAME randomized patients to either FFR‐guided revascularization in multi‐vessel disease or an angiographic approach where all stenoses ≥50% were stented; FFR reduced the number and length of stents placed and reduced the number of lesions considered significant. This lead to an improvement in composite outcomes of death, myocardial infarction, and repeat revascularization. FAME‐II randomized those patients with confirmed FFR≤0.80 to PCI with optimal medical therapy or optimal medical therapy alone. Two‐year follow‐up suggested the composite of death, non‐fatal MI and revascularization was significantly lower with PCI than medical therapy, although the majority of the events were urgent revascularization, and the trial was stopped early which limits its statistical power. Longer‐term follow‐up confirms the advantage noted at two years is sustained over a five year period.

Therefore, it is typical for revascularization to be offered when stenoses have FFR≤0.75, while deferral is more likely when FFR>0.80. For values in the “grey‐zone” (between 0.75–0.80), clinical judgement is required, combining knowledge of the patient’s clinical presentation with other testing. It is common practice to give additional doses of hyperemic agent when values are close to the threshold: higher doses can give confidence that maximal hyperemia has been achieved, but since flow is not being directly measured, caution is required since some changes can result from the hemodynamic disturbance of higher doses.

An area of great potential remains the use of FFR during routine clinical angiography. At present, FFR is used at the time of coronary intervention, either to defer a lesion when others are being treated, or to provide confirmation of ischemia when other tests are not available. Greater utility may be gained by performing three‐vessel physiological assessment at the time of angiography to objectively delineate the clinical significance of any stenoses; this will reduce the number of patients needing to return for further procedures and will offer more definitive diagnoses at the first procedure. The findings of studies suggest there may significant changes in medical decision making with the additional information [42,53].