Dr. Wissem Sdiri
Prof. Antoine Lafont,
Angiographic data are sometimes insufficient to assess the severity of a given coronary stenosis. This is usually the case in intermediate stenosis for which interventional cardiologists have 2 questions : can this lesion induce myocardial ischemia ? and consequently, does it require angioplasty ?
Stress echocardiography and stress perfusion scintigraphy can answer these interrogations with accuracy. However, non invasive tests have 2 limitations : they can be inconclusive and some patients undergo a coronary angiogram before a non invasive evaluation.
Fractional flow reserve (FFR) is an index derived from coronary artery pressure measurements, providing functional data through a simple and safe procedure. It is defined as the ratio between the maximal blood flow to the myocardium in the presence of a stenosis in the supplying artery and the theoretical normal maximal blood flow in the same area in the absence of the stenosis. To induce maximal hyperemia, some drugs are available: Adenosine (intracoronary bolus or intravenous infusion), ATP (intracoronary bolus or intravenous infusion) or Papaverine (intracoronary bolus). Each drug is used with a specific dosage, which is validated in humans to induce maximal hyperemia. In our institution, we use intracoronary bolus’ of Adenosine (40µg in the left coronary artery – 20µg in the right coronary artery). Adenosine induces hyperemia by stimulating specific receptors, mainly A2 arteriolar receptors. Therefore, there is no need to stop medicines such as nitrates, beta-blockers or calcium blockers. Another interesting feature of FFR, is that it is independent of haemodynamic conditions (heart rate, blood pressure, and contractility). In practice, a pressure guide wire is placed distal to the stenosis giving a distal pressure (Pd). Aortic pressure (Pa) is measured as usually through the guiding catheter. FFR is calculated at maximal hyperemia by dividing mean distal pressure by mean aortic pressure.
FFR = Pd /Pa
A cut-off value of 0.75 has been established in correlation with non invasive tests, to distinguish stenoses that can induce ischemia from those that do not. So, FFR is considered as an online scintigraphy, providing accurate data concerning functional severity of intermediate stenosis even in acute coronary syndromes without ST-segment elevation. More recently, some studies suggest that FFR, is feasible in infarct-related coronary arteries providing data regarding both ischemia and viability. Another application for FFR, is the assessment of stent deployment; this interesting field is investigated in the current FROST 4 trial. Unfortunately, FFR is still expensive so its use is limited to only a few centres. In conclusion, FFR is an accurate index for functional evaluation of intermediate stenosis, it can avoid abusive revascularisation, it shortens the length of hospitalisation and renders the interventional cardiologist more autonomous in his decisions.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
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Dr Wissem SDIRI, Dr. Antoine LAFONT Hopital Européen Georges Pompidou Université PARIS V, France
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