Anatomic assessment of coronary arteries by means of angiographySelective coronary cine-angiography was first performed in 1958 by Dr. F.M. Sones Jr. 1 For a long time, anatomical assessment by means of coronary angiography (CAG) remained the 'gold standard' for the evaluation of both, extent of coronary artery disease and severity of coronary stenoses. 2 In patients with symptoms and/or signs of myocardial ischemia, a CAG-based lumen diameter stenosis of more than 50%, as compared to the lumen dimensions in the adjacent normal (reference) vessel segments, generally was (and sometimes is) considered significant, and thus, a reasonable indication for coronary revascularization. 3 However, further research subsequently led to the knowledge that (so-called) "intermediate" coronary lesions with anatomically significant lumen diameter stenoses of 50-70% are often functionally non-significant, as only a minority of them cause myocardial ischemia. 4,5 Semi-quantitative assessment of coronary flow from coronary angiography In the 1980s, CAG was first used to qualify coronary flow velocity in the setting of patients with acute myocardial infarction. The Thrombolysis in Myocardial Infarction (TIMI) study group introduced the assessment of TIMI flow grade, with grade 3 representing normal coronary flow, grade 2 being flow that filled the entire artery but slower than in other coronary vessels, grade 1 representing partial filling, and grade 0 showing no filling of the coronary lumen beyond the obstructive lesion. 6 One decade later, the same research group refined the TIMI flow grades by the introduction of the TIMI frame count (TFC) approach. 7 Using predefined distal anatomic landmarks of the three major coronary vessels, TFC determines the number of frames required to fill the entire artery with dye, which allows to quantify coronary flow velocity.As in normal coronary arteries the TFC of the left anterior descending (LAD) was found to be significantly higher than that of the left circumflex (LCX) and right coronary artery (RCA), TFC measurements of the LAD were corrected by a factor (i.e., divided by 1.7) to determine the (so-called) corrected TFC (CTFC). Thereafter, this corrected index of coronary flow velocity was used in various clinical studies and randomized trials. [8][9][10][11][12] It is noteworthy that the value of TFC measurements is influenced by the cine frame rate of the CAG. The acquisition rate of the X-ray systems is dependent on the frequency of the electricity network. Therefore, in Europe the cine frame rate is 12.5 or 25 framesper-second (50 Hertz electricity supply), while in the USA that rate is 15 or 30 framesper-second (60 Hertz). 13 As restoration of epicardial coronary flow does not necessarily restore microvascular perfusion, CAG-based assessment of myocardial blush grade was introduced as a semiquantitative angiographic measure of myocardial perfusion in patients with acute
Principle and possible side effects of adenosine-based hyperemia inductionAdenosine is a purine nucleoside tha...