ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 occurs, and 2 (two) if the pain is impeditive (growing intensity) as exercise proceeds. In accordance with the results of the regression equation, patients are classified as follows: • High-risk group : patients with scores ≤ -11, with an annual cardiovascular mortality rate ≥ 5%. • Low-risk group : patients with scores ≥ 5, with an annual cardiovascular mortality rate < 1%. In clinical practice, when patients are considered high-risk, this reinforces a priori the indication for invasive study with the aim of managing and directing medical treatment, be it interventional or not, while always taking the possibility of improving morbimortality and quality of life into account. In patients with intermediates results, i.e., scores between > -11 and <+5, in order to reclassify risk, complementary exams associated with imaging, such as the following, may be required: - Myocardial perfusion scintigraphy (MPS) with ET or vasodilators. - Vasodilator stress cardiac magnetic resonance (technique associated with inability to exercise). - Doppler echocardiogram under stress or specific conditions. - Computerized angiotomography of coronary arteries. Finally, in patients considered low-risk, medical management is related to prevention measures. On the other hand, based on a growing base of evidence, these methods, 52 especially MPS, have become of paramount importance for quantifying ischemic area, even in patients who are considered high-risk, with the aim of assisting and directing the medical approach to be adopted, 53-58 notwithstanding the unavailability of information from randomized clinical trials such as the “Ischemia Study,” which will be able to assist in better management of patients with extensive areas of the myocardium at risk. 59 Furthermore, emphasis given to exercise as the primary stress-producing agent of choice within the cardiovascular system has become clear, given that it is the most physiological method for triggering myocardial ischemia, based on sympathetic stimulation and the increase in the main determinants of myocardial oxygen consumption (MVO 2 ), such as HR, blood pressure, and myocardial contractility. Likewise, exercise leads to coronary vasodilation through biochemical mechanisms, resulting in increased blood flow to the myocardium and greater oxygen supply, thus meeting the necessary demands imposed during the application of extreme effort. This ability to increase coronary blood flow, which reaches three to four times baseline values during peak exercise, in the absence of significant obstructive coronary lesions, conceptually represents the phenomenon known as “coronary reserve,” considered the main characteristic of MPS with radiopharmaceuticals. Moreover, with respect to the limitations and contraindications of this methodology, 60 joint analysis of both stress test and cardiac imaging exams will play a fundamental role in the medical decision-making process, albeit in view of previous clinical information or pretest probability of obstructive CAD. With relation to the main methodological aspects, the following stand out: • Prior venous access in an arm, in a “Y” shape (separate routes), for radiopharmaceutical injection during peak exercise and subsequent flush with saline solution, respectively. • Safety criteria for administering and interrupting stress should be in accordance with established guidelines, reinforcing the need for a maximum test. 61 • Fo l l owi ng i n t r avenou s admi n i s t r a t i on o f t he radiopharmaceutical, stimulate continuation of stress for 1 more minute. • When using MIBI- 99m Tc (absolute preference in Brazil), image acquisition follows conventional protocols (30 to 60 minutes after stopping stress). Variations in initial acquisition time depend on patient type (obesity, prior abdominal surgery, prominent extracardiac activity in the resting images phase. • When using thallium-201, considering the phenomenon of redistribution, images should be taken 10 to 15 minutes after stopping stress. Pharmacological tests: Represent excellent alternatives for evaluating patients with physical limitations or clinical impediments to undergoing efficacious exercise testing . The most frequent conditions are found in Table 10. They represent around 20% to 30% of all cases of scintigraphy referral and approximately 50% of elderly patients. 62 The drugs used in these circumstances are dipyridamole, adenosine or regadenoson, and dobutamine. These drugs induce maximum vasodilation and increase coronary flow, allowing for assessment of coronary reserve, with diagnostic and prognostic power similar to that of exercise, 63,64 which has recently been extended to elderly patients and women. 65,66 In cases of left His bundle branch block or artificial pacemaker with ventricular stimulation, the first option is a pharmacological test with dipyridamole or adenosine, with the aim of avoiding what are known as false-positive results (alterations in relative radiopharmaceutical uptake, in the absence of obstructive lesions). These are caused by atypical movement of the interventricular septum, which occurs in these situations and is accentuated when myocardial scintigraphy is performed with ET. Reduced radiopharmaceutical uptake is often observed in these patients and is most frequently related to the septal region, which may be exacerbated by the stress test, as increased HR increases paradoxical septal motion and, consequently, reduces perfusion in this wall. 67,68 Primary vasodilators: Dipyridamole, adenosine, and regadenoson (not available for routine clinical practice in Brazil) provoke a significant increase in coronary flow in normal arteries and a small or nonexistent increase in arteries with functionally significant stenosis, thus resulting in relative heterogeneity of flow between LV walls. During maximum vasodilatation, when the radioisotope is injected, the difference in relative radiopharmaceutical uptake in LV walls will also be observed, making it possible to diagnose coronary disease: • Dipyridamole: the total dose of dipyridamole is 0.56 mg.kg -1 up to a maximum dose of 60 mg or 6 vials (a 2-ml vial = 10 mg), administered intravenously (IV), preferably with a 4-minute infusion pump, diluted in 50 ml of saline 339