ABC | Volume 114, Nº3, March 2020

Original Article Candemir et al. Slow Flow and Magnetic Resonance Imaging Arq Bras Cardiol. 2020; 114(3):540-551 the control group and the MR negative group (11.15 ± 1.43 vs 9.74 ± 2.05; p=0.201) (Table 3). Discussion The main finding of this study was the detection of scar tissue in CMR in the patients with slow flow in the LAD. NT- proBNP values were higher in patients with slow flow and scar tissue in CMR. In addition, the exercise capacity of these patients was lower compared to the control group. Coronary slow flow patients have not previously been evaluated with CMR to detect any presence of myocardial fibrosis in the literature. In our study, we detected scar tissue in the myocardium in the LAD field in about half of patients with CSFP in the LAD. This finding was statistically and clinically significant when compared to the control group. However, we did not evaluate the patients with serial MRI examinations or serial NT-proBNP measurements. The absence of scar tissue in the remaining patients may be explained by this limitation of our study. The development of scar tissue in the myocardium requires a progressive process occurring as a result of continuous damage over years. Thus, the absence of scar tissue might have been due to timing of the assessment. As it is very well known, the process of atheromatous plaque formation takes many years, depending on the presence of cardiovascular risk factors, environmental conditions, genetic factors and the time period. The same factors may also apply to coronary slow flow. We have shown with this study that the CSFP is not harmless at all and that it can lead to scarring in the myocardial tissue at the end of the respective pathological process. The role of NT-proBNP in the pathophysiology of CSFP is not clear. It has been shown that B-type natriuretic peptide is secreted from cardiomyocytes in response to ischemia and that its secretion can also be independent of left ventricular wall stress. 17-20 Also, in addition to cardiac myocytes, fibroblasts can secrete BNP and cause fibrosis by induction of matrix metalloproteinases by releasing BNP. 21 In our study, the levels of NT-proBNP were not significantly high in patients with slow flow. However, they were found to be high in patients with slow flow, in whom scars were detected in CMR. It may be suggested that NT-proBNP levels are elevated only in the presence of sufficient fibrosis in response to coronary slow flow, which has led to the development of myocardial scar Figure 1 – Patient selection. CMR: cardiac magnetic resonance imaging. 543