ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 Figure 51 – Prognostic studies in patients with severe chronic coronary artery disease and ventricular dysfunction evaluating late survival with revascularization versus medical therapy following viability study via non-invasive testing. 201 Tl: thallium-201; FDG- 18 F: metabolic imaging with fluorodeoxyglucose labeled with fluorine-18; Dobut: doppler echocardiography associated with intravenous injection of dobutamine solution; Revasc: myocardial revascularization surgery; Pts: patients; Viable: viable myocardium. Adapted fromAllman KC, et al. 287 Note that in the presence of viable myocardium and clinical treatment, the rate of events was > 4 times (16%) higher than in the same situation with surgical treatment via myocardial revascularization (3.2%); however, in the situation of absence of viable myocardium, the comparison between clinical and surgical treatment showed no significant differences in mortality (6.2% vs. 7.7%, respectively). MEDICAL THERAPY × REVASCULARIZATION × VIABLE MYOCARDIUM ANNUAL EVENTS (%) 24 PROGNOSTIC STUDIES - 3,088 PTS REVASC CLINICAL VIABLE 201 Tl, 18-FDG, Dobut NOT VIABLE 3.2 16 7.7 6.2 quantity of viable tissue. Patients are typically prepared for imaging with administration of glucose overload and subsequent doses of insulin, prior to intravenous injection of 5 to 15 mCi of FDG- 18 F. Images are acquired 45 to 90 minutes after the administration of the tracer, lasting, approximately, 15 to 30 minutes. Low-dose CT is required for attenuation correction. The combination of perfusion and metabolism imaging via PET has a sensitivity of 88% and a specificity of 74% for myocardial viability. 284 Some differences exist for patients with diabetes, for whom the preferred form of viability evaluation is with 201 Tl or agents bound to 99m Tc. It is also important to remember that the radioisotope fluorine-18 or 18 F is produced in a cyclotron, consisting of the bombardment of enriched water labeled with oxygen-18 or 18 O and decaying via positron emission, with an energy range of 511 keV. Its half-life is 110 minutes, allowing for the best spatial resolution among radiotracers used for PET. When using PET for joint analysis of metabolism with FDG- 18 F and perfusion (positron emitters are not available for this in clinical practice in Brazil), an excellent predictive value for functional recovery has been observed. Measurements of MBF are typically performed with rubidium-82 ( 82 Rb) or ammonia labeled with nitrogen-13 ( 13 NH 3 ). Based on the concept of hibernating myocardium, segments with reduced perfusion, but with preserved FDG uptake (known as mismatches), are classified as viable, with functional improvements following adequate revascularization. However, when perfusion and FDG uptake are diminished or apparently absent (matches), this reflects an absence of viability (areas of fibrosis), which do not show improvements after revascularization. Finally, the combined approach to blood flow-FDG mismatches has been widely document as a predictor of post-revascularization regional improvements in motility, as well as improvements in symptoms of HF, exercise capacity, and prognosis. The PET and Recovery after Revascularization (PARR-2) study, 285 which is still the only randomized prospective study to evaluate the benefits of results of a management strategy assisted by PET in patients with severe LV dysfunction, evaluated 430 randomized individuals for viability study with PET or conventional treatment without the use of PET. Results of primary analysis after 12 months of follow-up have showed a tendency toward improved results in the FDG-assisted PET, which was not statistically significant. On the other hand, post-hoc analysis, including only patients who adhered to the management strategy recommended based on the findings of FDG PET, showed significant improvements in mortality with the PET-assisted approach, when compared to standard care. Di Carli et al. 286 demonstrated that small areas of viable myocardium (more than 5%), identified by PET, stratified patients into subgroups of high-risk of cardiac events in a year. Equally, comparative studies on viability between PET and SPECT with 201 Tl demonstrated agreement of results in 80% of cases. 10.7. Additional Information Based on Evidence within the Medical Decision-making process for Patients with Congestive Heart Failure, Decreased Left Ventricular Ejection Fraction, and Viable Myocardium A classic meta-analysis involving 24 studies and 3,088 patients (Left Ventricular Ejection Fraction – LVEF 32% ± 8%), with the use of different imaging methods, demonstrated that patients with viability had significant reductions in mortality when comparing surgical revascularization treatment and clinical treatment, with no benefits for either group in the absence of viability (Figure 51). 287 393