ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 curve for PET and SPECT was, respectively, 0.95 and 0.90 (p < 0.0001), showing a small superiority for PET. The second meta-analysis indicated 82 Rb as the most used tracer, resulting in higher sensitivity for PET. Specificity, on the other hand, although superior, was not statistically significant. 222 Regarding prognosis, similarly to SPECT, for which data are abundant, robust, and well established, normal myocardial perfusion with PET is indicative of good prognosis, with cardiac events varying between 0.09% and 0.9% during 1 year of follow-up, depending on the population analyzed. On the other hand, adverse events increase with the extent of perfusion defects on PET. A recently published register including more than 7,000 patients demonstrated that the hazard ratio of cardiac death increased with every 10% increment of extent of perfusion defects, classified as mild, moderate, and severe, respectively, hazard ratio: 2.3 (95%CI: 1.4–3.8; p=0.001); hazard ratio: 4.2 (95%CI: 2.3–7.5; p < 0.001), and hazard ratio: 4.9 (95% CI: 2.5–9.6; p < 0.0001), in relation to a normal exam. 221 8.5. Patient Preparation, Types of Stress, and Dosimetry Preparations include a 6-hour water-only fast. Patients should avoid caffeine and foods or medications containing xanthines (theophylline, theobromine) for at least 24 hours. Generally speaking, stress protocols are generic for all types of perfusion agents, bearing similarities to those of MPS with SPECT, with specific differences in accordance with acquisition protocols. Current dosimetry for studies with rubidium-82 ( 82 Rb) in adults, considering maximum administered activity per 60- mCi dose, may vary from 1.1 to 3.5 mSv of total effective dose. With the current advances in instrumentation of PET cameras, studies with good diagnostic quality may be acquired with injected activities that vary from 20 to 40 mCi per resting and stress dose, resulting in even lower exposure. In studies with ammonia labeled with nitrogen-13 ( 13 NH 3 ), the habitual activity is 10 to 20 mCi per dose (which corresponds to 1.48 mSv per dose). Doses of up to 25 to 30 mCi may be used in patients with high body mass index (BMI), with relatively lower dosimetry as a function of its shorter half-life and the low energy of its positron. The evolution of imaging systems has allowed for the development of PET/CT capable of performing hybrid imaging, or be it, using CT not only for attenuation correction but also for quantification of CS and acquisition of coronary angio-CT, in addition to allowing for the fusion of these images, facilitating the integration of anatomical and functional information. Another great advance is that of PET systems incorporated to PET/MR. This new hybrid imaging modality has enormous potential for structural- functional evaluation, tissue characterization, and reduced exposure to radiation. 229-231 This, thus, amplifies the possibility of developing new studies, with the aim of expanding data on clinical applications and diagnostic and prognostic benefits of PET in studies of more diverse cardiovascular conditions. Objective measures of coronary flow reserve will certainly be able to be extended to the MPS-SPECT method, providing evidence of nuclear medicine’s ability to carry out quantifications of MBF and allowing for additional parameters for evaluating perfusion, as well as myocardial reserve, with a resulting impact on clinical management of patients, which will objectively orient decisions about revascularization (Figure 18). 232 Provided that availability barriers are overcome and costs of both imaging systems and tracers are reduced, especially in developing countries such as Brazil, the growing application of this new methodology has a promising outlook in cardiology. Figure 18 – Coronary flow reserve (CFR). Left: In patients with high CRF, there were no statistically significant differences in adjusted rates of annual events, notwithstanding apparent reduction observed in patients who underwent angioplasty or coronary artery bypass graft (CABG). Right: In patients with low CRF, both procedures showed significant benefits in reducing events. Source: Adapted from Taqueti VR et al. 232 Adjusted Annual Event Rate (%) High CFR/ without CABG (n = 79) High CFR/ Angioplasty (n = 70) High CFR/ CABG (n = 17) Low CFR/ without CABG (n = 59) Low CFR/ Angioplasty (n = 84) Low CFR/ CABG (n = 22) p = 0.37 360