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 10 – Main indications for use of pharmacological stress in patients with contraindications or limitations to undergoing exercise stress 24,46 • Motor sequelae from cerebral vascular insufficiency and degenerative or inflammatory musculoskeletal pathologies • Compensated congestive heart failure • Chronic pulmonary obstructive disease with important functional restriction, but without recent hyperresponsiveness • Low functional capacity • Other non-cardiac conditions that result in an inability to exercise efficiently • Severe arterial hypertension • Complex ventricular arrhythmias triggered by effort • Pre-operative cardiological assessment for major abdominal vascular surgery • Presence of left bundle branch intraventricular conduction disorders • Risk stratification for recent evolution of myocardial infarction • Use of drugs that interfere with oxygen consumption elevation • Presence of artificial electric stimulation solution (SS). It may, alternatively, be injected manually (with a 20-ml syringe), using the same dilution. Alternatively, a more elevated dose of 0.84 mg.kg -1 may be used in select cases. The radiopharmaceutical is administered IV during hyperemia or maximum vasodilation, 2 to 4 minutes after the end of dipyridamole infusion (Figure 4). Dipyridamole inhibits the action of the enzyme adenosine deaminase, wich degrades endogenous adenosine, in addition to blocking reuptake of adenosine into the cellular membrane, with a consequent increase in extracellular concentration and resulting coronary vasodilation. Its biological half-life is approximately 45 minutes. • Adenosine: The usual dose is 140 μg.kg -1 .min -1 , and it must mandatorily be administered via a 6-minute continuous infusion pump, diluted in 50 ml of SS, with the injection of the radiopharmaceutical administered during the third minute via a different intravenous access (Figure 5). It is, also, possible to inject the solution for 4 minutes, in which case the radiopharmaceutical is administered during the second minute. 69 Because xanthines block the vasodilation effect, patients should be instructed to suspend them for 24 hours before a scheduled exam with dipyridamole or 12 hours before a scheduled exam with adenosine, in addition to any other drug or product, food, or drink that contains methylxanthines or theophyllines, including coffee, tea, soft drinks, chocolate, energy drinks, compound analgesics containing caffeine, especially for treatment of muscular pain or migraines, et al. Reference lists are available for consultation. 70 Adenosine induces coronary vasodilation via specific activation of A 2A receptors in the cellular membrane, resulting in increased coronary flow up to 4- or 5-fold resting values. Accuracy for detecting CAD with the use of MPS is comparable between both drugs. It is worth reiterating that, in exams using dipyridamole and adenosine, modifications in the ST segment occur relatively infrequently, even in patients with obstructive CAD (lower sensibility). In some instances, only the relative difference in flow observed in patients with different degrees of luminal obstruction and coronary reserve will determine perfusion defects, and ischemia will not necessarily be present. For this condition, collateral circulation is necessary, which causes coronary steal, with consequent alterations in contractility. Nevertheless, the sensitivity of scintigraphy images associated with the use of pharmacological agents or stress tests is similar. Adverse effects or “paraeffects” of using these drugs 23,71 occur in approximately 50% of patients with dipyridamole and in up to 80% of patients with adenosine. Common side effects include headache, dizziness, flushed face, feeling hot, chest pain, ST alterations and others (Tables 11 and 12). 72 These manifestations generally do not last long, and in most cases they may be reversed by administering intravenous aminophylline at 1 to 2 mg.kg -1 or 72 mg (3 ml) to 240 mg (10 ml or 1 vial) 2 minutes after injecting the radiotracer, when MPS is associated with dipyridamole. When adenosine is used, there is no need to inject an antagonist, given its ultrashort half-life, from 2 – 10 seconds, the recommendation being simply to interrupt the infusion. When it is not medically possible to perform either the physical stress or the pharmacological dilation modality with dipyridamole or adenosine, intravenous administration of dobutamine solution may be the best option for assessing coronary reserve flow, with regards to increased MVO 2 . Contraindications to dipyridamole and adenosine use are listed in Table 13. It is, finally, important to stress that, with both dipyridamole and adenosine, no significant increases are observed in MVO 2 , which, in clinical practice, is translated as the product of heart rate (HR) × systolic blood pressure (SBP), or the double product. During pharmacological stimulation, SBP values generally drop by around 10% while HR increases by approximately the same proportion, with no consequent increase in MVO 2 . Drugs that promote elevated myocardial oxygen consumption: These drugs represent an alternative for patients who cannot undergo ET or pharmacological stress with dipyridamole or adenosine . Examples include patients 340