Observational study of relevant electrocardiogram indexes of rat acute ischemic myocardial injury induced by different doses of isoprenaline

Objective To explore the reliability of relevant electrocardiogram(ECG) indexes in evaluating isoprenaline(ISO)-induced rat acute ischemic myocardial injury and provide reference for future scientific applications of these models. Methods Seventy male Wistar rats were randomly equally assigned to ten groups according to their body weight: 5,10,20,40,80,160,320,640, 1280 and 2560 μg/kg dose groups. All rats were tail intravenously given corresponding doses of saline diluted isoprenaline according to their body weight. Standard limb Ⅰ , Ⅱ, Ⅲ-lead ECG of all rats were recorded before, immediately after and 1,24,and 72 hour after injection, respectively.Changes of heart rate, T-wave amplitude of Ⅱ -lead and Q-T interval were measured. Results Significant differences were found in heart rates, T-wave amplitudes and Q-T intervals at different time points(F = 15.03,11.28,13.64, all P ＜ 0.01 ), while differences among the ten ISO-dose groups were statistically insignificant (F= 1.45, 1.17,1.09, all P ＞ 0.05). No interaction between observation time and ISO dose was observed on heart rates, T-wave amplitudes and Q-T intervals(F= 0.79,0.82,0.59, all P ＞ 0.05). Immediately after injection of ISO, the heart rates were significantly increased compared with that of pre-injection in all groups(all P ＜ 0.05), of which 320 and 640μg/kg dose groups increased most significantly [(550 ± 47), (521 ± 43)times/min]. T-waves decreased significantly compared with that of pre-injection (all P ＜ 0.01 ), and 20 μg/kg dose and above groups decreased particularly evident, and partly inverted. Q-T intervals of rats in each group were significantly shorter than that of pre-injection(all P ＜ 0.01 ), and 320, 640, 1280 μg/kg groups shortened more pronounced[(0.070 ± 0.006),(0.072 ± 0.005), (0.068 ± 0.005)ms]. One hour after injection, the heart rate of rats in each group decreased,except 320 and 640 μg/kg dose groups[(518 ± 43), (487 ± 36)times/min], which were still higher than that of pre-treatment[(450 ± 40), (448 ± 51 )times/min, all P ＜ 0.05], the rest groups no longer had significant differences (all P ＞ 0.05). ECG T-wave in each group was significantly recovered compared with that of instantly medication (all P＜0.05), and 40 μg/kg dose and above groups recovered more than a big margin, but there were still differences compared with that of pre-treatment (P ＜0.05), while T-waves of 40 μg/kg dose and below groups had returned to the level of pre-treatment. Q-T interval in each group had varying degrees of recovery, except 1280 and 2560 μg/kg dose groups[(0.080 ± 0.004), (0.076 ± 0.011 )ms]which were still less than that of pre-treatment[(0.086 ± 0.007),(0.085 ± 0.006)ms, all P ＜ 0.05], other groups had no significant difference compared with that of pre-treatment (all P ＞ 0.05). Twenty-four hours after injection of ISO, the heart rates of 1280 and 2560 μg/kg dose groups [(389 ± 31 ), (398 ± 23)times/min]decreased significantly compared with that of pre-treatment[(427 ± 43), (438 ±26)times/min, all P ＜ 0.05], while other groups had returned to the level of pre-treatment. Seventy-two hours after injection of ISO, the heart rates, T-wave amplitudes and Q-T intervals of all doses groups had returned to the level of pre-treatment (all P ＞ 0.05). Conclusions There has no significant ST segment in the electrocardiogram of rat.Isoprenaline has an exact effect on shortening Q-T interval. T-wave amplitude and Q-T interval can be used as reliable indexes of ECG for assessment of this animal model. Key words: Isoproterenol; Myocardial ischemia; Electrocardiography; Rats