ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 Table 16 – Types of existing receptors in the cellular membrane and responses to stimuli Type Resulting effects A1 Atrioventricular blockage A2a Coronary artery vasodilation A2b Peripheral vasodilation, bronchospasm A3 Bronchospasm 5.5. Image Generation and Perfusion Defects in Myocardial Scintigraphy with Radioisotopes Resting coronary flow is 1 ml.g.min -1 , increased 3- to 5-fold during maximal vasodilation or hyperemia, under physical or pharmacological stress (Figure 8). 28 In the presence of obstructive coronary lesions, resting coronary flow decreases when luminal narrowing is greater than 80%, due to exhaustion of the coronary reserve. When physical or pharmacological stress are applied, early exhaustion of the coronary reserve is observed, and it then exhibits a drop, generally beginning with lesions with luminal narrowing of 50%. 80 This information has currently been validated based on invasive measures of coronary flow reserve (CFR), fractional flow reserve (FFR), and instantaneous flow reserve (IFR), considered “standard” for characterizing myocardial ischemia; some have also been reproduced by non-invasive PET methods. 81-86 Tests with pharmacological stimulation using dipyridamole or adenosine associated with MPS are considered frequently to result in coronary flows in the range of 4 ml per gram of myocardium per minute, 87-89 generating homogenous relative uptake patterns of the radioisotopes in the myocardium, and scintigraphy images are considered normal when the coronary arteries are free of atherosclerotic processes. There are, however, specific situations in which patients with balanced multivessel disease (lesions in 3 arteries with similar coronary reserve) in which perfusion images appear with apparently homogeneous radiopharmaceutical distribution. 90 From the conceptual point of view, it is necessary to comprehend that the generation of scintigraphy images is based on relative radiopharmaceutical uptake, which is injected intravenously during physical exercise or pharmacological test, predominantly in the LV myocardium. Comparison of radiopharmaceutical uptake between ventricular walls is expressed in images based on a scale of colors, created by specific computer programs, which, in addition to allowing for subjective analysis of perfusion, make semi-quantitative and quantitative evaluation of affected myocardial area possible. 5.6. Possible Scintigraphy Imaging Results, Using Qualitative, Semi-quantitative, and Quantitative Analyses Visual or qualitative analysis: By simply inspecting images resulting from perfusion tomography and ventricular function exams (Gated-SPECT technique), it is possible to assess blood flow and regional contractility of the LV myocardium indirectly. Tomography images are reconstructed as multiple slices along the anatomical axis of the LV, defined as corresponding regions and respective relations with coronary territory. The slices are taken on Figure 7 – Myocardial perfusion scintigraphy associated with intravenous administration of regadenoson, a specific agonist of adenosine A 2 A receptors in the cellular membrane. Activation of the receptor produces coronary vasodilation with a consequent increase in flow, similar to dipyridamole and adenosine. Maximum plasma concentration is reached 1 to 4 minutes after injection, with a biological half-life of 2 to 4 minutes during the first phase. The intermediate and the late phases follow, with approximate duration of 30 minutes (loss of pharmocodynamic effect) and 2 hours (decline in plasma concentration). The radiopharmaceutical, MIBI- 99m Tc or Tetrofosmin- 99m Tc, is injected at the moment of maximum hyperemia, close to 30 seconds after injection of regadenoson. Injection of Regadenoson Injection of the radiopharmaceutical Saline infusion 0.4 mcg/5mL IV injection for 10 to 20 seconds 10 to 20 seconds after saline infusion 5 mL REGADENOSON Time (seconds) OPTIONAL Light exercise 344