Coronary angiography is an invasive procedure to detect the severity of CAD. However, the visual evaluation of the diameter of the vessel is not always sufficient. In the last years, stent decision-making uses new functional measurements: the Fractional Flow Reserve (FFR) and the Instantaneous Wave-Free ratio (IFR). The first index is adenosine-dependent with a cut-off of 0.86: coronary stenosis under this level were treated. Conversely, the second one is an adenosine-independent index. A value under 0.9 suggested a flow reduction. Recently, to test the use the two methods an Hybrid IFR/FFR approach was provided.
During angiography, IFR was performed. Coronary stenoses < to 0.86 were treated. In other direction, a value > 0.94 deferred revascularization and, in the range of 0,86-0.94, FFR guided therapy. Using this approach the 60 % of patients were free from intravenous vasodilator infusions that are expensive. So, there was a lowering of healthcare costs and adverse effects, for patients. Import clinical trials provide evidences and the usefulness of this complementary strategy. This caused a relevant improvement both in patient outcomes than in time of revascularization. However, the IFR in clinical routine still requires prospective clinical endpoint trial evaluations.
fractional flow reserve, istantaneous wave-free ratio, hybrid strategy, physiological angiographic assessment
Coronary angiography is an invasive procedure to detect the severity of CAD. However, the visual evaluation of the diameter of the vessel is not always sufficient. The detection of an intermediate stenoses needs a physiological assessment of its severity, especially in patients without a prior stress-imaging, when it is not available or his results are borderlines. In the cath lab, this assessment is done using Fractional Flow reserve: the ratio, at maximum hyperemia, between mean distal coronary pressure and the aortic one. This index is based upon the principle that the maximum functional capacity of a patient is linked to the maximal flow during hyperemia o exercise, when the blood flow and perfusion pressure are proportional (Figure 1).
According to Defer , Fame I  and Advise Ii trials , when coronary physiology is used to perform revascularization, the procedure is safe.
If a FFR ≤ 0.80 revascularization procedure will be recommended to improve :
- angina symptoms, unresponsive to maximal therapy;
- patient's prognosis, in the setting of a left main disease (>50 %);
- a proximal LAD stenosis or a multivessel disease (>50 %) with a left ventricular failure (FE< 40%).
Maximal hyperemia was reached by adenosine administered intravenously.
However, many adverse reactions could occur as bronchoconstriction, significant hypotension, flushing, chest discomfort and, sometimes, arrhythmia: second- or third-degree AV block. So, today during cardiac catheterization a new diagnostic tool was performed: the Instantaneous Wave-Free ratio (IFR). This represents a new adenosine-independent index. The IFR is the diastolic ratio between the distal coronary pressure and the aortic one, in a specific period. So, both flows than pressures are linearly related and a value below 0.9 is suggested of flow restriction (Tables 1 and 2).
The Advise study demonstered as this new index of stenosis severity was comparable to FFR . According the Advise registry, the classification of a population with intermediate stenosis revealed an excellent agreement between the FFR and IFR 's one . Furthermore, in the Clarify study, a futher hyperemia, by the administration of adenosine and the reduction in resistance, did not improve diagnostic categorization. So, iFR is an alternative method to FFR . Recently, to test the use of the two methods an Hybrid IFR/FFR approach was provided . During angiography, IFR was performed. Coronary stenosis with an index of < to 0.86 were treated. In the range of 0,86-0.94, FFR guide therapy. Conversely, a value > 0.94 deferred revascularization. Using this approach the 60 % of patients were free from intravenous vasodilator infusions that were expensive. So, there was a lowering of healthcare costs and of adverse effects, for patients. Import clinical trials as the Advise II  the Resove  and the Sintax II  provide evidences and the usefulness of this complementary strategy.
Today, combining IFR with FFR in a hybrid strategy offer a physiological assessment, ease to use, that enhaces accurance during decision-making. This new approach can predict the signiﬁcance of many intermediate stenoses, especially when non-invasive stress imaging is unavailable or contraindicated.
So, there was a relevant improvement both in patient outcomes than in time of revascularization. About the 60% of patients were free from more expensive intravenous vasodilators with a lowered healthcare costs and adverse effects. However, according to Hale et al. , IFR in clinical routine still requires prospective clinical endpoint trial evaluations.
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