Читать книгу Interventional Cardiology - Группа авторов - Страница 194

There has been considerable debate over the merits of resting and hyperemic indices. Given the totality of evidence, it is clear that patients managed with either approach have good outcomes with little to discern between the approaches at one year [18,84]. As FFR has been in routine use for longer, many physicians feel a greater degree of comfort in its application, albeit it at greater expense, procedure time and intra‐procedure patient discomfort. Operators should be reassured that outcomes are equivalent and systematic assessment against other ischemic parameters show there is little to discern between the indexes. Where there is doubt, a resting index can always be supplemented by hyperemia using a “Hybrid” approach.

There are physiological reasons that resting indices have a closer relationship with flow‐based parameters [85]. There appears a closer relationship between iFR and CFR – a parameter that integrates the assessment of both an epicardial stenosis and microvascular function (Figure 7.9). Truly ischemic patients are those where there is concordance between pressure gradients and reduction in CFR [85,86]. These patients benefit most from revascularization and have high event rates if deferred. In those in which there is pressure loss (FFR and NHPR), but CFR is preserved, there may be merit in deferring the lesion [86]. This is being assessed prospectively in the DEFINE‐FLOW study. In patients in which iFR is non‐ischemic and FFR is ischemic, CFR is likely to be in the normal range, as measured by flow velocity [85] or PET [87]. In studies following patients who are deferred with this physiological pattern, the event rate is the same as those with entirely negative physiological parameters [88].

Figure 7.9 Examples of cases in which low FFR values are generated by high magnitudes of hyperaemic flow. In both cases, baseline instantaneous wave‐free ratio (iFR), coronary flow velocity reserve (CFVR) and hyperaemic stenosis resistance index (HSR) were normal, indicating a mild, not flow‐limiting stenosis. In (B) a SPECT myocardial perfusion scan also confirms the absence of myocardial ischaemia. In these cases, hyperemic pressure is not reflecting flow and is not representative of ischaemia. Adapted from Petraco et al (2014).

In patients with left main stem stenoses, there is longer‐standing data to support decision making with FFR. Recent studies have shown similar outcomes in those managed by iFR [80]. For both parameters, study design constraints prevent a definitive answer outside a dedicated randomized study.

Resting indices are particularly helpful in serial stenoses; this extends to discerning hemodynamic significance of stenoses separated by diffuse disease. Both approaches permit mapping coronary vessels, but resting indices have less flow interaction meaning post‐PCI results are more predictable.