ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 either use “pixels” as units of measurement for resolution or are transformed into a digital matrix, emphasizing that “pixel” values of images of the ventricular myocardium are directly proportional to physiological cardiovascular properties. Physical phenomena such as the “Compton scattering effect,” the “photoelectric effect,” and geometric distortions should, however, be considered, 146 given that they tend to interfere with direct proportionality, in a manner that is decreasing as equipment and image reconstruction techniques technologically evolve. Furthermore, another factor related to acceptance and preference of nuclear cardiology for detecting myocardial perfusion defects is the elevated, superior resolution contrast (allowing for differentiation between normal and decreased perfusion) in comparison with other imaging methods, 147,148 even considering lower spatial resolution. There is also a peculiar aspect, namely, that the myocardium (organ of interest) appears emphasized due to the greater brightness in comparison with underlying structures (background) and, consequently, provides excellent signaling, which facilitates the development of integrated, computerized algorithms for SPECT and PET techniques. These programs, which automatically process and objectively quantify images, have good comprehension, and they are well validated and internationally utilized. 149-151 From the conceptual point of view, it is necessary to grasp that scintigraphy image generation is based on relative uptake of the radiopharmaceutical in the myocardium of the LV, when it is injected intravenously during physical exercise or pharmacological tests. The comparison of radiopharmaceutical uptake between ventricular walls is expressed in images based on a color scale, created by specific computer programs which, in addition to allowing for subjective analysis of perfusion, make it possible to conduct semi-quantitative and quantitative evaluation of affected myocardial area. During visual evaluation of scintigraphy images, the following are taken into consideration: homogenous distribution patterns or normal radiopharmaceutical uptake in the myocardium, transient low uptake suggestive of ischemia, fixed low uptake suggestive of fibrosis, and partially reversible low uptake suggestive of ischemia associated with fibrosis 24,152 (Examples are provided in the Methodology and Tutorial Cases sections). 7. Evaluation of Patients with Potential Acute Coronary Syndrome – Algorithms in the Chest Pain Unit 7.1. Introduction Continuous chest pain is one of the most common symptoms in emergency units, accounting for approximately 8 million annual visits in the USA. 153 Although approximately 50% of patients are admitted for diagnostic definition, only 30% of visits will correspond to the condition of acute coronary syndrome (ACS), 2% to 4% of whom will be inappropriately discharged from the hospital (Figure 15), leading to serious risks of severe events, in addition to legal-medical problems. Considering these implications, as well as hesitation to discharge patients with acute myocardial infarction (AMI), assessment of patients with atypical chest pain in emergency unit has emphasized admission for posterior clarification and risk stratification. With the development of more sensitive cardiac biomarkers in conjunction with more precise non- invasive exams and validated clinical parameters, early Figure 15 – Chest pain spectrum in emergency units, with clinical implications, forms of presentation of acute coronary syndrome and available methods for investigation and risk stratification. Cor: coronary; Myo: myocardium. NSTEMI: non-ST-segment-elevation myocardial infarction; STEMI: ST-segment-elevation myocardial infarction. Source: Adapted from Amsterdam EA. 154 SCENARIO - CLINICAL PRESENTATION “CHEST PAIN” 8 MILLION/YEAR – EMERGENCY CHEST PAIN/SYMPTOMS – ISCHEMIA < 5% STEMI 25% NSTEMI PAIN UNITS NEW BIOMARKERS RISK SCORES NON-INVASIVE IMAGING MYO. – COR. ARTERIES DIAGNOSTIC LOSS > 2% 160,000 CHALLENGE - FAST IDENTIFICATION RISK-ADJUSTED MORTALITY 2x > MINORITY RISK OF DEATH 353