ABC | Volume 113, Nº4, October 2019

Review Article Magalhães et al. Principles of MPCT Arq Bras Cardiol. 2019; 113(4):758-767 CCTA Evaluation (% stenosis) Myocardial CTP assessment (presence of perfusion defect) CCTA reclassification (after reading Myocardial CTP) < 30% 30-49% 50-69% Not interpretable ≥ 70% No defect Predominantly fixed Predominantly reversible Negative Positive Negative Positive Presence of stenosis > 50% associated with perfusional stress defect? Figura 2 – Workflow for combined CCTA + myocardial CTP analysis (modified from Magalhaes et al 57 ). The TPR is calculated by the average subendocardial density (in Hounsfield Units) divided by the average of the subepicardial density of each myocardial segment. This relationship showed that Myocardial CTP can detect and quantify perfusion defects compared with SPECT, 30 and has excellent accuracy to identify perfusion defects after pharmacological stress associated with significant coronary obstruction by invasive coronary angiography. 52 TPR less than 0.85 should be considered the cutoff value for identifying ischemic segments. 52 Tomography SSS should be calculated based on the sum of perfusion defect of the 17 segments predefined by the American Heart Association, ranging from a scale of 0-4 for each segment (0 – normal; 1 – discrete; 2 – moderate; 3 – important and 4 – transmural perfusion defect). SSS values for ischemia quantification are: less than 4 normal, between 4 and 8 discrete, between 9 and 13 moderate, and greater than 13 important. Report Myocardial CTP assessment should be divided into qualitative and quantitative analysis. The report must contain the examiner's visual and subjective impressions, followed by the quantitative assessment (TRP and SSS). The reversibility of perfusion defects is fundamental information and should be addressed in the report, as it reflects the myocardial ischemia itself. The most important part of the report is the integration of anatomical and perfusion findings. The examiner should clearly define whether there is a correlation between luminal obstructions and perfusion defects, as well as the extent of perfusion defects and reversibility as they define the therapeutic approach. 60 The main elements of the report are expressed in Table 3. Limitations Myocardial perfusion study is advantageous when in conjunction with the anatomical assessment of the coronary arteries, as it benefits from the combined assessment. Thus, it is a limited strategy when considered in isolation, given exposure to ionizing radiation and iodinated contrast, which can be avoided in other diagnostic methods. Because it uses additional doses of radiation and contrast when compared to coronary tomography alone, Myocardial CTP should be used with caution in patients with renal failure or undergoing other examinations employing ionizing radiation over a short time. The use of vasodilatory pharmacological stress should be carefully evaluated in patients with any clinical or hemodynamic instability, as well as in patients with atrioventricular blocks, chronic obstructive pulmonary disease and asthma. Future perspectives As previously mentioned, the use of dynamic perfusion by tomography allows the evaluation of myocardial iodine contrast kinetics, making it possible to quantify MBF. Additionally, the use of dual energy techniques (two x-ray tubes operating simultaneously at different voltages) allows to create an “iodine map” for the quantification of perfusion defects. Although such techniques are already available, further studies are needed to assess the impact of these approaches on clinical decision-making, as well as the increased supply of equipment that allows the use of this technique, which is still scarce in Brazil. Recently, a new approach has emerged in the functional assessment of coronary artery disease by CT, known as CT‑derived FFR. Although it uses a completely different technique, it has the same purpose of Myocardial CTP, using 763