IJCS | Volume 33, Nº4, July and August 2020

323 Table 1 - Evaluation of blood pressure in hypertensive (L-NAME and SHR) and normotensive (WIS and WKY) rats at 15 weeks of age WIS L-NAME WKY SHR Systolic pressure 118.8 ± 16.53 156.4 ± 30.35* 119.5 ± 11.64 139.4 ± 12.84* Diastolic pressure 96.28 ± 20.05 133.6 ± 31.35* 95.85 ± 16.58 114.6 ± 13.85* Pulse pressure 22.54 ± 10.44 22.83 ± 4.91 23.61 ± 5.23 24.86 ± 5.56 Mean pressure 106.9 ± 22.58 145.2 ± 30.28* 107.1 ± 15.57 127.1 ± 12.88* Ejection time (s) 0.0608 ± 0.0083 0.0736 ± 0.0385 0.0616 ± 0.0092 0.0690 ± 0.0220 Non-ejection time (s) 0.0777 ± 0.0123 0.0897 ± 0.0196 0.0811 ± 0.0122 0.0895 ± 0.0268 Cycle duration (s) 0.1389 ± 0.0187 0.1496 ± 0.0245 0.1421 ± 0.0208 0.1555 ± 0.0246 Time to peak (s) 0.0309 ± 0.0115 0.0399 ± 0.0076 0.0230 ± 0.0060 0.0405 ± 0.0100* Mean diastolic pressure 102.9 ± 24.64 141.4 ± 29.89* 103.0 ± 16.16 128.2 ± 7.81* Blood pressure parameters of Wistar (WIS), Wistar-Kyoto (WKY), NG-monomethyl-L-arginine methyl ester (L-NAME)-induced hypertension, and spontaneously hypertensive rats (SHR) at six and 15 weeks of age. Data are presented as mean ± SD. *p < 0.05 compared to controls (WIS vs. L-NAME; WKY vs. SHR), n = 6. Electrocardiographic (ECG) analysis: The six-week-old L-NAME rats showed no ECG changes compared with WIS. However, the 15-week- old L-NAME rats exhibited increase in QT, QTc and JT intervals when compared to their controls, suggesting impaired ventricular conduction after the intervention (Figure 1, Table 2). SHR at sixweeks of age showed a decrease in heart rate (HR) and an increase in the RR interval when compared with WKY. At this age, SHR also exhibited changes in atrial electrical conduction, such as increased PR interval and P-wave duration. Changes in ventricular function were also observed, with a decrease of QT and QTc intervals, increase in Q wave amplitude and decrease in R and S waves’ amplitudes. By visual analysis, the ECG revealed a delay in atrial conduction and shortening in ventricular conduction compared with six-week-old WKY (Figure 1, Table 2). The 15-week-old SHR continued to exhibit lower HR and increased RR and PR interval than WKY, indicating an impairment of atrial conduction with increase in P-wave duration. These rats failed to show a decrease in QT, QTc, JT and P wave amplitude when compared to WKY, probably due to a failure in ventricular conduction at 15 weeks of life, and a decrease in S wave amplitude at six weeks. Ventricular extrasystole followed by compensatory pauses may characterize impaired ventricular conduction in the SHR when compared with WKY (Figure 1, Table 2). Regarding the differences between hypertension models used in this study, our results showed that six- week-old SHR exhibited several changes when compared to L-NAME rats, such as a decrease in HR, increase in RR and PR intervals and duration, increased P wave amplitude, as well as a reduction of QT interval, QTc and JT. At 15 weeks of age, SHR exhibited higher RR interval and P amplitude than L-NAME, an increase in P wave amplitude and shorter JT interval when compared to L-NAME (Figure 1, Table 2). Analysis between the control rats demonstrated that six-week-old WKY had a reduction in PR interval and an increase in QRS interval when compared with WIS. At 15 weeks of age, WKY showed an increase in the QT interval when comparedwith theWIS (Figure 1, Table 2). Discussion In both hypertension models, the animals showed higher systolic, diastolic and mean pressure values at 15 weeks. Ribeiro et al., 22 identified progressive increase in blood pressure in L-NAME rats after 4-6 weeks of life, reaching 164 ± 6 mmHg when compared with 108 ± 3 mmHg in controls. SHR rats developed hypertension at 4–6 weeks of age without any type of intervention and Grassi-Kassisse et al. ECG in hypertension models Int J Cardiovasc Sci. 2020; 33(4):321-328 Original Article