FRACTIONAL FLOW RESERVE (FFR)
Fractional Flow Reserve (FFR) is used to determine if a cardiac patient really needs a stent or bypass surgery or can be kept only on medicines avoiding any procedure. This highly scientific and evidence based procedure is beneficial to the patient as FFR technology not only saves lives while avoiding unnecessary surgery but also helps patients to save cost. Fractional flow reserve – guided stent implantation has been established to be economically attractive in cost-effectiveness analysis.
Patients with heart disease have blockages in the blood vessels (arteries) of their heart. When these blockages limit the amount of blood able to flow through the artery, they are “hemodynamically significant” or “serious blocks.” These “serious or tight” blockages often cause frightening symptoms such as chest discomfort or shortness of breath and can cause a heart attack. Blockages in blood vessels are identified during diagnostic Coronary Angiogram which forms the basis of most decisions whether the particular patient needs a stent or bypass or only medicines. This approach is perfectly reasonable when the Angiogram clearly demonstrates either a severely blocked blood vessel or a normal one. However, Angiography has well-known limitations and the significance of lesions of moderate severity is often difficult to determine based on just the Angiogram.
The blockages are often assessed visually and the narrowing is described as 50% or 90% depending on the visual severity of the narrowing. Most of the blocks above 70% are treated by stents or bypass surgery. But very often we come across blockages around 60% or 70% where the decision to treat by surgery or medicine is not clear. This uncertainty may result in inappropriate care with stenting of non-flow limiting lesions (non – serious) or failure to treat significant or serious blocks which can cause a heart attack.
Now with advances and availability of scientific data, Fractional Flow Reserve (FFR) procedure is done to measure how “tight or serious” a blockage is. The FFR is defined as the ratio between distal heart blood vessel pressure and aortic pressure, both measured simultaneously at maximal flow using a tiny coronary pressure guide wire. FFR is determined by a carefully calibrated sensor that measures the blood pressure upstream and downstream (before and after the block) after the administration of medicine like adenosine to induce maximum flow.
Fractional Flow Reserve is physiologically based and describes the ratio of the maximum achievable flow in the presence of a stenosis to the theoretical maximum flow in the same vessel in the absence of a stenosis. It takes into consideration the multiple, complex variables influencing coronary flow including lesion severity, lesion length and collateral flow.
Thus, if the FFR finds the difference between the two measurements is significant, then the blockage is considered to be significant. FFR has been shown to correlate very well with non-invasive stress testing and is considered to be complementary to a conventional Angiogram, particularly when the tightness of a blockage is difficult to establish by Angiography or when patients have not had non-invasive stress testing.