ABC | Volume 110, Nº4, April 2018

Original Article Winter et al High-intensity training after AMI Arq Bras Cardiol. 2018; 110(4):373-380 Therefore, the aim of this study was to compare the effects of high-intensity training on post-AMI ventricular function with those of moderate-intensity training. Methods We conducted an experimental study according to the norms and ethical principles of the Brazilian College of Animal Experimentation (COBEA), and approval by the ethics committee for animal research of Pontifical Catholic University of Parana. First, 40 adult, male Wistar rats weighing 250–300 grams were selected by convenience. The animals had water and food ad libitum . The rats were anesthetized with intramuscular ketamine (Ketamin ® / Cristalia - 70 mg/kg) and xylazin (Calmiun ® / Agener União- 20 mg/kg). Then, the animals were intubated and mechanically ventilatedwith oxygen at 2.5mL/min (small‑animal volume). The animals were placed in the supine position (with the body slightly inclined to the right to facilitate the access to the area that would be operated), and all four limbs were fixed using adhesive tape. The chest was shaved and disinfected with povidone-iodine. A left posterolateral thoracotomy was performed at the third intercostal space; as the left pleura was open, the pericardium was removed to expose the operation site. The left auricle was isolated, and the left coronary artery, identified between the pulmonary artery and the left atrium, was ligated with a blue, non-absorbable 7.0 monofilament polypropylene suture thread. The infarcted area was identified by its different color. The heart was then repositioned within the chest, the lungs hyperinflated and the thoracic wall sutured using a non-absorbable, 4.0 nylon monofilament. 7 Two M-mode echocardiographic examinations (MyLab 40, Esaote ® ) were performed with a 7.5-10.0 MHz sector transducer. The parameters analyzed were left ventricular ejection fraction (LVEF[%]), end-diastolic diameter (EDD[mL]) and end-systolic diameter (ESD[mL]). Rats with a LVEF > 50% in the first echocardiographic exam were included in the study. The sample was composed of 29 animals, which were randomized using piece of folded papers inside a white envelope. The envelopes were drawn by the main author, and the animals allocated to one of the three groups – control group (CG, n = 10), continuous training group (CTG, n = 9), and interval training group (ITG, n = 10). The ideal training intensity was determined by a swimming test, with incremental load and control of lactate production. The animals were put in a tank filled to a depth of 40 cm of water (deep enough to prevent the animals to sustain their bodies with their tails on the bottom). 7 Then, the rats underwent swimming exercise with progressive, additional load (proportional to body weight) - 4.0; 4.5; 5.0; 5.5 e 6.0% of body weight for five minutes each. 8 The main purpose of this test was to determine the lactate threshold (LT), which was used as the cutoff point for the continuous and interval training loads. Then 25 µL of blood samples were collected from the tail of the animal at rest and at each load progression. 9,10 Lactic acid production was analyzed using a portable lactate analyzer (Accutrend ® ). Lactate concentration values were organized in an excel spreadsheet, and a line graph obtained for each animal. LT was visually identified and defined as the point where linearity was lost. This process was performed for both training groups in the swimming tests, one day after each echocardiographic examination. According to the lactate test results, training intensities prescribed to the CTG and the ITG were at the LT and above the LT, respectively. The CG did not undergo physical training. Training program of CTG and ITG consisted of a 42-day macrocycle, divided into six 7-day microcycles of 30 exercise sessions (five a week, once a day). The overload method defined for both groups was of volume, i.e., a weekly increase in the time of swimming (min). In the first two weeks of training, CTG underwent swimming training for 10 minutes continuously. In the third and fourth week, the rats swam for 15 minutes, and for 20 minutes in the last two weeks. The ITG underwent five 2-minute sessions with 2-minute intervals between them and 1:1 training density in the first two weeks. In the third and fourth weeks, the rats swam seven 2-minute sessions, with the same interval between them. Finally, in the two last weeks, the animals swam ten 2-minute series, with the same interval between them. Our outcome measures were LVEF, ESD, ESD and the effect of training (lactate curve). Within-group and between group comparisons of these parameters were performed by a blinded investigator. 9 At the end of the experiment, the animals were euthanized by sodium pentobarbital (i.v. 200-250 mg/Kg). Statistical analysis Continuous variables were expressed as mean ± standard deviation. Comparisons of quantitative variables were performed by one-factor analysis of variance (ANOVA), and the Newman-Keuls test was used for multiple comparisons. Comparisons between the two evaluations within each group were performed by Student’s t-test for dependent variables. Normality of the variables was tested by the Shapiro-Wilks test. Statistical significance was set at p < 0.05. Analyses were performed using the Statistica software, version 8.0. Results Pre- and post-training echocardiographic results and results of lactate tests were compared within and between groups. Tables 1 and 2 describes the results of within and between group comparisons, respectively, of LFEV, and left ventricular EDD and ESD, and Tables 3 and 4 describes the results of within and between group comparisons, respectively, of pre- and post‑training results of lactate testing with incremental load. Graphs 1 and 2 show comparative results of pre-training versus post-training lactate in ITG and CTG, respectively. Discussion The main findings of the present study were: 1) No differences were found in within-group and between-group comparisons of echocardiographic parameters in CTG and ITG; 374