ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 and consequent estimation of functional significance of coronary stenoses, evaluation of the efficacy of therapeutic interventions, and stratification of ACS risk. One of the principal indications for MPS during the first 12 hours of symptom onset is to decide whether or not to hospitalize a patient with chest pain and suspected CAD, when ECG was normal or had non-specific alterations. Resting MPS, when it is performed in an early phase of attendance and considered low-risk, determines a low index of future cardiac events. Recent studies have demonstrated that, when ACS is suspected, the use of resting perfusion images with radiopharmaceuticals 175,176 is also associated with shorter hospital stays and lower costs, and it is additionally able to reduce unnecessary hospitalizations. 177,178 Furthermore, numerous observational studies have demonstrated a high NPV for normal resting perfusion images, with the objective of ruling out AMI or short-term cardiac events. 179 In a study by Schaeffer et al., 180 479 patients underwent resting MPS and were followed for 16 months. Of these patients, 434 had “normal” resting MPS, and 45 had “abnormal” resting MPS. In the normal group, only 3 patients (0.7%) had severe cardiac events, showing a NPV of 99.3%. 180 Equally, multiple evaluations have demonstrated the efficacy and safety of MPS with SPECT for assessing patients with chest pain in the emergency unit. 181-183 Population samples involved, however, were more heterogeneous and had higher numbers of risk factors for CAD. MPS effectively foresaw which patients would require coronary angiography. Nabi et al. related that 38.3% of patients with abnormal MPS underwent revascularization, while 0.9% of patients with normal MPS subsequently underwent coronary intervention. Of patients with myocardial area at risk (ischemia) involving > 10% extent in perfusion images, 55% underwent revascularization. 182,183 The study known as the PREMIER trial by N Better et al. 184 evaluated the performance of resting MPS in investigating chest pain in the emergency room with 356 low- to intermediate-risk patients, from 8 developing countries, including 2 Brazilian centers. The primary outcome considered included the compound events of death, non- fatal AMI, recurring angina, and coronary revascularization over 30 days, and the results reaffirmed the association between normal images and a good NPV (99.3%) for severe events (death or AMI). 184 Moreover, it is worth highlighting that the presence of resting perfusion alterations (abnormal scintigraphy) was the only variable independently associated with the primary outcome (adjusted OR = 8.19, 95% CI: 4.10–16.40, p = 0.0001), with even higher expression when only patients who received injections during episodes of pain were considered (adjusted OR = 17.35). On the other hand, results considered high-risk indicated worse prognoses for future cardiac events (death, AMI, myocardial revascularization surgery, or percutaneous intervention). 185,186 The Emergency Room Assessment of Sestamibi for Evaluation of Chest Pain (ERASE) Study, which evaluated patients with ACS and normal or non-diagnostic ECGwho were still in the emergency room, observed admission rates of 54% in patients who underwent MPS and 63% in other patients, suggesting that the initial strategy of resting scintigraphy is satisfactory, based on the fact that it demonstrates good risk stratification capability. 184,186 International guidelines recommend the use of resting myocardial perfusion images for acute chest pain as a class I recommendation with level of evidence A for risk stratification of patients with suspected ACS and non- diagnostic ECG. 187,188 Time of radiopharmaceutical injection: The main applications of MPS within the first hours of a patient’s arrival at the hospital are: • Radiopharmaceutical injection (technetium-99m-labeled sestamibi / MIBI or tetrofosmin, also known as 99m Tc- sestamibi and 99m Tc-tetrofosmin), while resting, during an episode of chest pain, with normal or non-specific ECG , with the objective of rapid diagnostic definition. • Radiopharmaceutical injection while resting, in the absence of chest pain, with normal or non-specific ECG , when the symptom has ceased less than 6 hours prior, but preferably within the 2 preceding hours. Wackers et al. 179 have demonstrated that, in cases where injections are administered up to 6 hours after pain, in ACS, there is an 84% incidence of perfusion abnormalities; this decreases to 19%when intravenous radiopharmaceutical administration occurred between 12 and 18 hours after the last episode of pain. Kontos et al. 176 found no reduction in sensitivity for identifying patients who evolved to AMI or revascularization when the injection was administered during the moment of pain or up to 6 hours after the cessation of the symptom. Ta k en a s a who l e , pe r f u s i on ima g i n g w i t h radiopharmaceuticals for evaluation of acute chest pain does not present any formal contraindications; it is well tolerated by most patients, and the quantitative assessment of information about ischemia is of special importance to the clinical decision- making process. PET: In a retrospective study conducted with more than 7,000 patients who presented at the emergency unit with chest pain, 189 92.5% of patients with positive stress or resting PET were diagnosed with ACS, by cardiac catheterization, electrocardiographic alterations, or positive cardiac biomarkers. In patients with reversible perfusion defects while resting or under stress (positive PET) who underwent cardiac catheterization, 87% were considered to have significant CAD. For patients without reversible perfusion abnormalities whose exams were classified as negative, no deaths were informed during the 30-day follow-up period. PET has a significantly better spatial resolution and higher sensitivity when compared to MPS. In Brazil, the elevated costs and low availability of this technology for patients with ACS are, however, limiting factors to its routine use. UA and NSTEMI: Patients whose clinical conditions indicate a high risk of AMI or UA should undergo hemodynamic study. For those with low to intermediate risks whose unstable angina (UA) has been clinically stabilized, MPS has shown an important value for risk stratification. 190 Additionally, it assists in diagnosis and medical management. It is recommended within the first hours of the patient’s arrival at the hospital. Cases with a history of chest pain, whose biochemical markers, nevertheless, show no alterations, with normal or non-diagnostic ECG are considered candidates. When 356