Gabor Toth (University Heart Centre Graz, Graz, Austria), Bernard De Bruyne (Cardiovascular Research Center Aalst, OLV Clinic, Aalst, Belgien) and others outline, in the Journal of the American College of Cardiology, steps for standardising how fractional flow reserve (FFR) is performed in clinical practice. In this interview, Toth talks to Cardiovascular News about the need for FFR standardisation.
In what ways could FFR practice differ between laboratories?
In general, no two laboratories have the same habits even for the most basic details such as anticoagulation, angiography or pressure measurements. Therefore, it is not surprising that there are also differences in FFR measurements. However as clinically crucial decisions are often based on these measurements, precision–and thus standardisation—of the process are paramount.
What are the potential consequences of having heterogeneous FFR approaches?
Heterogeneity goes along with variability, and variability is one of the main reasons for imprecision. And the latter generates uncertainty and subjectivity, which is not affordable in clinical decisions.
Your standardisation paper, in the setting of stable coronary disease, states FFR should be used on clinical grounds rather than “strict angiographic criteria”. Please can you expand on what you mean by this?
Currently the 50% diameter stenosis is still considered as the cornerstone of defining “coronary artery disease” and is still used for decision-making (Genders et al, Eur Heart J 2011). However, everyone easily understands that there is a huge variability in the acquisition of angiographic measurements, making it vague if it stands alone—especially, when we realise that the relationship between morphology and physiology is massively elusive. Therefore even though angiography will still remain the roadmap, it should only be used for decision-making about revascularisation when the percent diameter stenosis is in the extremes (<30% and >90%).
What does your paper recommend about the use of FFR in patients with acute coronary syndrome?
There are good data proving that FFR can be reliably used in the setting of acute coronary syndrome in non-culprit stenoses. So far we have no data to support FFR in culprit lesions (Fearon et al. JACC 2016).
What are your paper’s key recommendations about the materials (eg. guidewires) and practicalities use in FFR?
There are no key recommendations about material. All the presently available wires are validated and they have comparable performance. Again with the idea of standardisation and accuracy, we advocate to use always the same wire (from the same vendor) when an operator has built up experience with it. One would only suggest to “try out” another system when the number of measurements is very high.
Finally the goal is not more and not less, but simply to measure, record and store accurately a mean pressure proximal to the lesion and a mean pressure distal to the lesion during maximal hyperaemia. It is not rocket science!
You also advise to “always use the same means of producing hyperaemia”. Why is this?
The very concept of FFR is valid only during maximal macro- and microvascular vasodilation. More intuitively, it sounds logical to “test” a lesion under condition of maximal flow—just like one tests an aortic stenosis with dobutamine, diabetes with a glucose tolerance test, a plane in a wind tunnel, or a student with an exam.
What do you hope are the general take-home messages of the paper?
Simplify, standardise and store!