IJCS | Volume 33, Nº3, May / June 2020

270 obtained by Stoletniy and col.8. These authors showed that the QTc increased from rest to stress in patients with ischemia documented by myocardial scintigraphy, and that it did not increase from rest to stress peak in patients without myocardial scintigraphy documented using radioisotope techniques. We speculate that QTc is, ultimately, a marker of myocardial ischemia, with no strict connection with the degree of obstruction in large coronary arteries. The QTc delta also showed significant statistical difference between the groups. However, in order to test the theory that supports the concept of QTd, we decided to scketch a line graph that represented each individual in the three groups. Our concern was that the QTc and QTc delta values would show only the statistical difference between the means of the three groups (extreme QTc values of few individuals of one group can affect the mean and not necessarily represent the behavior of the rest to stress condition variable). Corroborating the results of the QTc dispersion of effort, nineteen patients from the TP group presented increased QTc from rest to stress conditions (Figure 3), whereas seven individuals showed a reduction. In contrast, in the TN group, five people presented increased QTd and nine reductions (Figure 5). The FP group maintained similar behavior as the TP group. In FP, fourteen patients increased the QT dispersion and nine reduced it (Figure 4). In order to statistically test the behavior of each group in relation to the QTc dispersion of effort and at rest, we used a paired T-test for each group, and obtained significant difference between the TP group means from rest to stress conditions, and a a trend to increased QTc in the FP group. The TN negative group did not show significant changes between the QTc pre- and postexercise means. We conclude that QTc behaves, predominantly, with an increase on exertion in patients with myocardial ischemia;and tends not to change significantly in patients without ischemia. Our study has some limitations that should be pointed out. First, our sample was small so we could not obtain a highly reliable cutoff point for QTc. Still, we must remember that our QTc cutoff point was quite similar to the ones found by other authors. Secondly, the methodology we used to measure the QTI – as far as we know - is unprecedented in the literature. Thus, our data must be confirmed by other similar studies. Our results can only be considered for a coronary population with no previousAMI or ventricular dysfunction. Finally, this is a database retrospective study with all the limitations inherent to this type of study. Conclusions Based on our results, we believe that QT dispersion – is spite of being a “crude” marker of ventricular repolarization heterogeneity – is sensitive to stress- inducedmyocardial ischemia and can aid in the diagnosis of chronic CAD. Author contributions Conception and design of the research: Barcelos AM, Mill JG. Acquisition of data: BarcelosAM, Rodrigues SL, Mill JG. Analysis and interpretation of the data: Barcelos AM, BaldoMP,Rodrigues SL, Mill JG. Statistical analysis: BarcelosAM, BaldoMP, Rodrigues SL, Mill JG. Obtaining financing: Barcelos AM. Writing of the manuscript: Barcelos AM. Critical revision of the manuscript for intellectual content: Barcelos AM, Baldo MP, Rodrigues SL, Mill JG. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding There were no external funding sources for this study. Study Association This article is part of the thesis of master submitted by Alexandre Maulaz Barcelos, from CEAP - Centro de Ensino e Aperfeiçoamento em Pesquisa - Hospital Evangélico de Vila Velha. Ethics approval and consent to participate This study was approved by the Ethics Committee of the Hospital Universitário CassianoAntônio de Moraes under the protocol number CAAE: 06177412.1.00007051. All the procedures in this studywere in accordance with the 1975 Helsinki Declaration, updated in 2013. Informed consent was obtained from all participants included in the study. Barcelos et al. QT interval dispersion in exercise test Int J Cardiovasc Sci. 2020; 33(3):263-271 Original Article