Since the late 1950s, coronary angiography has been regarded as the "golden standard" for the diagnosis of coronary heart disease. Up to now, textbooks still use the diagnostic criterion of epicardial coronary artery stenosis (>50%). However, since the 1990s, the advent of fraction? Owreserve (FFR) has challenged the diagnostic criteria of coronary artery disease based on coronary angiography, especially the previous idea of deciding whether or not to make PCI decisions for patients based on the results of coronary angiography has been questioned. A series of studies have confirmed that FFR can accurately evaluate the relationship between coronary artery disease and myocardial ischemia, and then guide the formulation of reasonable treatment decisions, improve the prognosis of patients, and save medical costs. At present, FFR is defined as the functional evaluation of coronary artery disease to evaluate whether coronary artery disease induces myocardial ischemia or not. FFR-guided vascular reconstruction is called functional vascular reconstruction. It is unanimously recognized that FFR is the "golden index" of functional evaluation of coronary artery disease. It also marks that the diagnosis and treatment of coronary heart disease has entered the post-coronary angiography era, that is, the functional era. Nowadays, the emerging techniques or indicators for assessing coronary function are becoming more and more mature.
FFR defines the critical value of myocardial ischemia as 0.75 or 0.80. At present, the latter is commonly used. The application of FFR confirmed that "lesions are not equal to myocardial ischemia, lesions of the same degree are not equal to the same degree of myocardial ischemia". The results of FAME subgroup analysis showed that there was a high mismatch between the degree of anatomical stenosis and functional measurements of lesions with diameter stenosis less than 90%. Only when angiographic stenosis was more than 90%, the anatomical and functional characteristics of lesions were highly consistent. FFR detection also found that the same degree of lesion in the proximal part of the great vessels and in the branches or distal part of the myocardial ischemia caused by the degree of difference. PCI treatment of non-induced myocardial ischemia defined by FFR does not benefit patients, but only medical treatment of FFR-induced myocardial ischemia defined by patients with short-term symptoms difficult to control or ACS to accept (emergency) revascularization treatment. These representative conclusions fully reflect the clinical value of FFR.
In order to popularize and standardize the application of FFR in China, the Interventional Cardiology Group of the Chinese Medical Association was commissioned to compile a consensus of Chinese experts, which was published in the Chinese Journal of Cardiovascular Disease in April 2016. The consensus includes five parts: the definition and theoretical basis of FFR, the methodology of detection, the judgment of ischemic threshold, the recommendation of clinical application and the prospect. Consensus recommendations in clinical application include indications, sources of evidence and precautions for FFR application in single isolated lesion, multi-vessel lesion, left main lesion, single-vessel series or diffuse lesion and bifurcation lesion, and also emphasize how to apply FFR in ACS patients. The consensus is concise and concise, but it is comprehensive, easy to understand and master, and practical. I believe that the publication of this consensus will play a very good role in promoting the wide use of FFR in China.
II. Evaluation Indicators of Non-drug Dependent Coronary Function
The detection of FFR requires the use of drugs such as adenosine or ATP to induce the maximum expansion of microcirculation. The side effects of drugs limit the application of FFR in some patients, and increase the operation steps and prolong the operation time. Some non-drug dependent functional indicators are well correlated with FFR, including:
(1) resting trans-stenosis pressure ratio (Pd/Pa): Pd is distal stenosis pressure, Pa is coronary orifice pressure. The positive predictive value (PPV) of resting Pd/Pa < 0.85 predicting FFR < 0.75 was 95%, while the negative predictive value (NPV) of resting Pd/Pa < 0.93 predicting FFR > 0.75 was 95.7%; that of resting Pd/Pa < 0.87 predicting FFR < 0.80 was 94.6%, and that of Pd/Pa < 0.96 predicting FFR > 0.80 was 93%. The retrospective study used resting Pd/Pa as the first time to determine the drug treatment, and PCI was performed at < 0.86. The standard of treatment was whether FFR was < 0.80 or not at 0.87-0.99. The results showed that the 5-year event-free survival rate of patients with Pd/PaFFR hybridization-guided treatment strategy was 70.8%, similar to 76.3% of patients with FFR-guided treatment strategy.
(2) instantaneous waveform-free Ratio (iFR): iFR is the ratio of distal lesion to oral pressure in waveform-free period of cardiac cycle. It has a good correlation with FFR (r=0.90). The diagnostic accuracy is 95%, PPV is 97%, NPV is 93%. Some studies used iFR < 0.86 as the threshold (PPV92%) for PCI, while iFR > 0.93 as the threshold (NPV91%) delayed PCI. Adenosine was only used to detect FFR in patients with iFR between 0.86 and 0.93. This method of iFR-FFR hybridization can reduce the use of adenosine by 57%, and has 95% consistency with the detection of FFR only.
(3) Contrast medium induced Pd/Paratio (CMR): The osmotic pressure of contrast medium can also induce a certain degree of coronary microcirculation dilatation. During the operation, 6 ML-10 ml contrast medium was injected into the coronary artery instead of adenosine to induce the secondary maximum dilatation of the coronary artery, and then Pd/Pa was detected. CMR was strongly correlated with FFR (r=0.94). The threshold value of predicting FFR < 0.80 was <0.83 (specificity 96.1%, sensitivity 85.7%). When CMR < 0.88, FFR was > 0.80 (accuracy 85%, specificity 78.9%, NPV 100%, PPV 63%). When CMR was between 0.84 and 0.87, it was suggested to use CMR/FFR hybridization to evaluate lesions in order to reduce adenosine use. Personal experience shows that the above three functional indicators are consistent with FFR, CMR > iFR > Pd/Pa.