Physiological assessment with fractional flow reserve (FFR) is an established approach for determining the need for intervention in patients with stable coronary artery disease. However, the ability of FFR to accurately assess diffuse or tandem lesions is limited.1 Cardiovascular News explores how pullback assessment with instant wave-free ratio (iFR) Scout (Philips Volcano) software may be able to provide accurate assessment of these lesions.
There is no doubt that physiological assessment with FFR provides advantages over angiographic assessment. The 2009 FAME (FFR vs. angiography for guiding PCI)2 study, for example, found that routine measurement with FFR in patients with multivessel disease undergoing percutaneous coronary intervention (PCI) with a drug-eluting stent was associated with a significant reduction in the study’s composite endpoint of death, non-fatal myocardial infarction, and repeat revascularisation at one year. However, FFR requires the administration of adenosine to achieve stable maximal hyperaemic flow. Intravenous adenosine requires a venous sheath, adds considerable cost in certain markets, and adds time to the procedure. Also, it can cause side-effects. Ciro Indolfi (Division of Cardiology, University Magna Graecia, Catanzaro, Italy) comments that “up to 20% of patients” who receive adenosine “feel uncomfortable due to chest pain, dyspnoea, or flushing”. He adds that the prolonged procedure time with FFR, because of the need for adenosine, may dissuade some operators from using FFR—“especially in patients with multivessel disease.”
“In light of these facts, the development of hyperaemic agent-free indices represents an attempt to further simplify intracoronary pressure-derived measurements with the objective of increasing the adoption of physiological assessment to improve patient management,” Indolfi reports.
One such adenosine-free approach is iFR, which is measured in the wave-free period when resistance is naturally stable (and thus, there is no need for maximal hyperaemia via adenosine infusion). Indolfi says: “From the patient perspective, in my experience, iFR is very well tolerated in terms of the time required for achieving the result and the side-effects associated with the technique.” Also, he comments that he and his colleagues demonstrated, in the FORECAST study,3 that iFR is particularly useful in the evaluation of non-culprit lesions in acute coronary syndrome patients with multivessel disease.
Furthermore, iFR may provide advantages when pullback assessment is required. Farrel Hellig (Cathlab Director, Sunninghill Hospital, Johannesburg, South Africa; Division of Cardiology University of Cape Town, Cape Town, South Africa) explains that typically with FFR or iFR, a “spot” assessment is performed by pushing the pressure wire distally beyond all lesions to determine if the sum of lesions in the vessel is significant: the cut-offs for significance are ≤0.89 with iFR and <80 with FFR. However, he adds that the therapeutic approach is problematic if a vessel contains multiple lesions—for example, those with tandem lesions or those with diffuse disease. Hellig says: “You have to decide whether to treat all of the lesions in the vessel, just some of them, or none of them. You need to know how long the stents should be. Sometimes, if the patient has diffuse disease, you do not know where (according to the angiogram) the main lesion is located in the vessel or if there are any lesions that can be treated because individually they are not significant (despite an overall significant FFR measurement).”
Therefore, in these cases, the operator needs to “pullback” the pressure wire over the vessel to better assess the lesions it contains. The aim with pullback assessment is to identify the lesion that is contributing the most to the ischaemia and then, once that has been identified and treated, to determine which (if any) other lesions in the vessel require treatment. The ultimate goal is, at the end of the procedure, be certain that you have removed all of the significant ischaemia in the vessel.
With iFR pullback (after initial iFR or FFR has indicated that the vessel contains a significant lesion), using the iFR Scout software, the transducer is slowly pulled back across the vessel and the operator, via the iFR monitor, identifies where there is a sudden “step up” in the iFR measurement. They then assess the relative change at each of the points where there has been a step up to determine the lesion that is making the biggest contribution to the overall ischaemia in the vessel. That lesion is then addressed with PCI and afterwards, an iFR measurement is again taken at the distal end of the vessel. If that indicates the vessel no longer contains significant ischaemia, no further treatment is required. However if significant ischaemia is indicated, pullback assessment with iFR Scout is repeated to identify each lesion in turn that is the biggest contributor to the overall ischaemia. This process is continued until all significant lesions in the vessel have been identified and treated.
Nijjer et al1 have demonstrated the value of this approach. In a study of 32 coronary arteries with tandem/diffusely diseased vessels, there was little difference between the predicted iFR measure (prior to the PCI) and the observed iFR (after PCI). They conclude: “iFR measurements during continuous resting pressure pullback provide a physiological map of the entire coronary vessel. Before a PCI, the iFR pullback can predict the haemodynamic consequences of stenting specific stenoses and, thereby, may facilitate the intervention and stenting strategy.”
Hellig notes, in his opinion, that pullback assessment with iFR Scout provides “better discriminatory information” than pullback assessment with FFR “because you have much more discrete steps with iFR, which means it is easier to read the relative contribution of each lesion”. He adds that hyperaemic flow, as used in FFR, “changes a great deal” after PCI. Nijjer et al1 agree that pullback with FFR is problematic, noting: “Removing a stenosis by intervention will increase hyperaemic flow, which alters the significance of secondary lesions. Because the change in flow can be unpredictable for a given stenosis, predicting the haemodynamic impact of removing a stenosis is difficult and not readily practical in the catheter lab.”
By contrast, Hellig states, resting flow “does not change significantly after PCI”—making prediction of iFR measurements after a stent has been placed reliable.1
Therefore, of the available options for pullback assessment, the iFR Scout may provide the most reliable measurements. Hellig believes that the use of pullback with iFR Scout may lead to better patient outcomes because it may enable you to avoid the use of “longer stents and overlapping stents, both of which can lead to worse long-term outcomes.”
Indolfi, whose experience of using pullback assessment with iFR Scout is “positive”, concurs with this view. He uses the software “mainly to select the most significant segment in the setting of diffuse and long lesions to reduce the lengths of stent required to reduce the risk of late and very late stent thrombosis”.
- Nijjer et al. JACC: Cardiovascular Interventions 2014; 7: 1386–96.
- Tonino et al. N Eng J Med 2009; 360: 213–24.
- Indolfi et al. Int J Cardiolol 2015; 178: 46–54.
This article has been sponsored by Philips Volcano. The views expressed are those of the physicians and do not necessarily reflect those of the company or those of Cardiovascular News