ABC | Volume 110, Nº2, February 2018

Original Article Rabelo et al The Presence and Extension of Myocardial Fibrosis in the Undetermined Form of Chagas’ Disease Arq Bras Cardiol. 2018; 110(2):124-131 Figure 1 – Rassi score in the different clinical forms of Chagas’ disease. LV: left ventricular. Low risk Intermediate Risk High Risk 25 25 75 100 22 0 0 0 0 54 10 20 30 40 50 60 70 80 90 100 Cardiac form with LV dysfunction Cardiac form without LV dysfunction Indeterminate form (IIQ: 1-5) in cardiac form without LV (p = 0.18). In those with ventricular dysfunction, the percentage of fibrosis was higher than in the other groups, occurring in 23 of the 25 subjects (92%), with a compromised area of 15.2% (IIQ: 7.8-25); p < 0.001 (Figure 2). The impact of myocardial fibrosis The LV ejection fraction was significantly lower in individuals with late enhancement when compared to subjects without enhancement (69 ± 13 versus 48 ± 19%); p < 0.0001. A negative correlation was observed between the extent of fibrosis and ejection fraction (r = 0.565; p < 0.001). Through linear regression analysis, progressive reduction of the ejection fraction was observed at each percentage increase in the area affected by fibrosis. This analysis showed a regression coefficient ( β ) of -0.968, which corresponds to the estimated reduction in the ejection fraction of the LV at each 1% increase in the area of fibrosis (Figure 3). There was a progressive increase in the amount of fibrosis in the different classes of the Rassi score, when subdivided into low, intermediate and high risk. The high-risk group had 13.8% (QI: 9 - 19) versus 4.9% (QI: 1 - 17) in the medium risk versus 0% (QI: 0 - 5) in the low risk group (p = 0.003). There was no difference in fibrotic mass between the low and intermediate risk classes (p = 0.19), nor was there a difference between intermediate and high risk (p = 1.0). Severity of the disease in its indeterminate form versus in its cardiac form without left ventricular dysfunction The left ventricular ejection fraction (LVEF) in individuals in the indeterminate form was 72 ± 8%, which is similar to the LVEF of patients in the cardiac form without ventricular dysfunction 67±6%; p=0.09. There were noNT-proBNP levels (125 pg/ml versus 159 pg/ml, p = 0.61), ultrasensitive CRP (4.6 mg/L versus 2.5 mg/L; p = 0, 40), TNF-alpha (0.9 pg/ml versus 1.2 pg/ml, p = 0.56), interleukins (p = 0.35), IFN-gamma (2.7 pg/ml vs. 3 3 pg/ml; p = 0.56) and MET (10 vs. 9.4, p = 0.66) achieved through exercise testing and the location of late enhancement (p = 0.44) when comparing patients in the indeterminate form with those in the cardiac form without dysfunction (Table 2). All 17 individuals in the indeterminate form were classified as low risk according to the Rassi score. While 16 individuals were shown to be in the cardiac form without dysfunction, 12 (75%) were considered low risk and 4 were considered intermediate risk; p = 0.04. Discussion The present study highlighted the presence of myocardial fibrosis in patients in the indeterminate form of Chagas’ disease. It was present in a frequency and extension similar to that of the group who had the disease in the cardiac form without ventricular dysfunction. Additionally, it was shown that ventricular function and clinical parameters are similar between these two forms. CMR has been used for decades for the anatomical and functional evaluation of the heart. It is important due to the fact that it is non-invasive, does not use ionizing radiation, and has a high resolution, which allows for multiple studies concerning cardiac anatomy, function and tissue characterization with the late enhancement technique. 19-21 Previous studies have validated the quantification of myocardial fibrosis using CMR in populations with Chagas' disease. 22,23 In 2005, Rochitte et al. 17 evaluated CMR with the use of the late enhancement technique in 51 patients with Chagas' heart disease, and found fibrosis in 68.6% of all of the individuals evaluated, and in 100% in those with ventricular tachycardia. 17 Regueiro et al. 23 found fibrosis in patients living outside the endemic area of the disease in a distribution of 7.4% of those in the indeterminate form, 15.8% 127