ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 increases the risk of ventricular arrhythmia. The sympathetic nervous system is an important trigger of major arrhythmic events by means of global cardiac adrenergic hyperactivity and heterogeneity of regional myocardial sympathetic activity. 322 Evaluation of the autonomic nervous system via myocardial scintigraphy (MS) with MIBG- 123 I may be useful in diverse clinical situations. The presence of denervated yet viable myocardium and the magnitude of denervation are potential markers of an individual’s susceptibility to triggering of severe arrhythmias. Several studies have demonstrated the ability of scintigraphy with MIBG- 123 I to identify patients at higher risks of developing spontaneous ventricular tachyarrhythmia, appropriate ICD shock, 351,352 and sudden cardiac death. 353-356 When analyzing the possibilities of scintigraphy imaging results, the finding of a mismatch between perfusion and myocardial innervation characterizes a scenario of higher risk for ventricular arrhythmia. 350,351 The denervated regions respond to sympathetic stimuli differently than normal myocardium. This electrophysiological heterogeneity may serve as a substrate for VT and ventricular fibrillation (VF). In the same manner, tomography images (SPECT) of cardiac scintigraphy with MIBG- 123 I are useful for recognizing increased arrhythmogenicity. A prospective study of 50 patients with antecedents of myocardial infarction who underwent SPECT imaging with MIBG- 123 I and perfusion SPECT perfusion with Tetrofosmin- 99m Tc showed, via multivariate analysis, that a late MIBG- 123 I SPECT defect score of ≥ 37 was the only parameter capable of differentiating the group of patients who presented VT induced by electrophysiological testing, with a sensitivity of 77% and a specificity of 75%. 357 There were no significant differences in late HMR and the mismatch scores obtained by subtraction of perfusion and sympathetic innervation between the groups with positive and negative induced VT. 356 Moreover, the Prediction of Arrhythmic Events with Positron Emission Tomography (PAREPET) study evaluated quantification of denervated myocardium in 204 patients with ischemic heart disease (LVEF ≤ 35%), by means of PET imaging with 11 C-meta- hydroxyephedrine (HED- 11 C), labeled with carbon-11. Perfusion and myocardial viability have also been characterized with 13 N-ammonia and 18 F-fluordeoxyglucose, respectively. The primary study objective was to observe the occurrence of sudden cardiac death, defined as arrhythmic death or ICD firing due to VF or VT > 240 beats/minute. After 4.1 years of follow-up, sudden cardiac death of 16.2% was registered. The quantification of infarction volume and LVEF were not factors predictive of sudden cardiac death. However, patients with higher volumes of denervated myocardium (33±10% versus 26 ± 11% of the LV; p = 0.001) showed sudden arrhythmic death more frequently. The authors of this study concluded that, in ischemic cardiomyopathy, sympathetic denervation evaluated by HED- 11 C PET predicts sudden arrhythmic death regardless of LVEF and infarction volume. This information may improve identification of patients who will most likely benefit from ICD implant. 358 One of the most peculiar aspects of the natural history of chronic Chagas cardiomyopathy is the occurrence of severe ventricular arrhythmia in individuals with preserved LV global systolic function which may evolve to sudden death during early phases of the disease. 359,360 In 43 patients with chronic Chagas cardiopathy and LVEF ≥ 35%, the correlation between extent of sympathetic denervation, myocardial fibrosis, and severity of ventricular arrhythmias was investigated. Patients were divided into 3 groups, according to the presence of sustained VT, non-sustained VT, and the absence of VT on 24-hour Holter. Sympathetic denervation was evaluated via SPECT imaging with MIBG- 123 I and myocardial fibrosis via SPECT with 99m Tc-sestamibi. The sums of perfusion scores (quantity of fibrosis) were similar in the 3 groups. The summed difference score betweenMIBG- 123 I and Sestamibi- 99m Tc, which evaluated the extension of denervated yet viable myocardium, was significantly larger in the group with sustained VT on Holter (score of 20.0 ± 8.0), when compared to the group without VT (2.0 ± 5.0; p < 0.0001) and NSVT (11.0 ± 8.0; p < 0.05). In conclusion, the occurrence of ventricular arrhythmias with different degrees of severity is quantitatively correlated with the extension of cardiac sympathetic denervation, but not with the extension of fibrosis, suggesting that myocardial sympathetic denervation plays a role in the generation of ventricular arrhythmia related to chronic Chagas cardiopathy. 361 Sympathetic denervation may also occur in patients with stable angina in the absence of infarction. Cardiac scintigraphy with MIBG- 123 I may show inervation defects in these cases, in the absence of perfusion defects. Sympathetic nervous fibers are more susceptible to oxygen privation than cardiomyocytes and the occurrence of myocardial ischemia may thus lead to transient sympathetic denervation. 362 The fact that recovery of inervation may be a slower process also makes it possible to use myocardial scintigraphy with MIBG- 123 I as a marker of ischemic memory in patients whose chest pain has resolved few hours or days prior. Regional alterations of cardiac sympathetic activity may also be seen in primary arrhythmic conditions, in the absence of CAD, 363 in Brugada syndrome, 364 in hypertrophic cardiomyopathy, 365,366 and in arrhythmogenic RV dysplasia. 367 These findings in patients with primary arrhythmias support the potential use of cardiac scintigraphy with MIBG- 123 I for identifying patients at a risk of sudden cardiac death, who may benefit from ICD implant. 13.3.3. Cardiotoxicity Due to Chemotherapy Over the past decades, there have been great advances in cancer diagnosis and treatment, offering oncology patients reduced mortality, increased survival, and better quality of life. On the other hand, progress in oncological treatment results in higher exposure to the cardiotoxic effects of chemotherapy. Screening for the occurrence of cardiotoxicity (CTX) is highly recommended before, during, and after the completion of chemotherapy. Several methods and diagnostic indexes have been suggested for the detection of CTX and therapeutic strategy planning. Although serial measure of LVEF by conventional echocardiogram is the most utilized strategy for monitoring myocardial damage, it does not appear to be sensitive enough to detect patients with risks of developing significant CTX in early phases of chemotherapy administration. 323 The potential use of cardiac adrenergic imaging for monitoring the cardiotoxic effects of chemotherapy has been debated. 368-370 There is evidence that reduced cardiac uptake of MIBG- 123 I precedes ejection fraction deterioration. 371 402