| Part oneChanges in cardiac sympathetic activity and electrophysiological characteristics in dogs with acute anterior myocardial infarctionObjective:Observed effects of acute myocardial infarction model in dogs after ligating first diagonal branch and the changes of cardiac sympathetic activities and cardiac electrophysiological properties of acute myocardial infarctionMethods:12 mongrel dogs were randomly assigned into two groups, the MI group (n=6) and sham-operated group (n=6). MI group were ligating the first diagonal branch of the left anterior descending coronary artery (LAD) to establish the canine model of acute myocardial infarction. The animals in sham-operated group also underwent thoracotomy and pericardiotomy, but not coronary artery ligation. Norepinephrine (NE) and epinephrine(E) levels in the coronary sinus (CS) blood, the ventricular effective refractory period (ERP) were all measured during the experiments.The incidence of VA was monitored among both groups. The pathological detection of infarction and infarct area were also performed then. Results were shown by x ±s, NE and E changes were test by independent-samples T test. ERP changes were tested by paired t test, pairwise comparisons between different regions were calculated by LSD method, arrhythmia induced rates were compared by chi-square test, p<0.05 was considered statistically significance. All statistical analyzes were performed by SPSS 21.0 software.Results:1. All dogs in MI group was successfully established acute myocardial infarction, Changes of ECG and cardiac tissue color were confirmed;2. NE, E concentrations in MI group compared with the previous ligation were significantly higher (708.28±35.83 ng/L vs 199.20±26.09ng/L, p<0.05; 79.48±6.17 ng/ L vs 32.93±3.74 ng/L, p<0.05), they were also higher than the sham group (708.28±35.83 ng/L vs 199.32±12.41ng/L, p<0.05; 79.48±6.17 ng/L vs 37.72±8.09 ng/L, p<0.05);3. ERP values in MI group were significantly shorter compared with the previous measurement before ligation(139.33±1.78ms vs 153.2±1.55ms, p<0.05).In MI group, ERP shorten-values in infarct area was significantly lower than the other areas, (23.33±1.97ms vs 11.33±2.50ms vs 13.83±1.60ms, p<0.05), sham group was not observed inconsistencies;4. In the sham group there was only one dog (16.7%, n=6) induced polymorphic ventricular tachycardia or ventricular fibrillation; while the MI group had three dogs (50%,n=6) induced polymorphic ventricular tachycardia or ventricular fibrillation.There was no significant difference between both groups (p>0.05);5. Pathology showed no intimal injury and thrombosis, no significant myocardial damage, staining the sympathetic nerve fibers showed no damages in sham-group; In MI group was observed regional myocardial infarction changes such as dark red myocardium, coagulation necrosis, edema, hemorrhage and neutrophil infiltration.TH staining showed the injured sympathetic fibers.Conclusion:The regional catecholamine concentrations in acute myocardial infarction dogs were significantly increased, the local effective refractory period was shorter and there were uneven shortness of ERP among different regions.Part TwoEarly intravenous low/high doses of Metoprolol in myocardial infarction dogs on the effects of cardiac sympathetic activity and electrophysiological propertiesObjective:Observed effects of early intravenous low/high doses of Metoprolol in myocardial infarction dogs on cardiac sympathetic activity and electrophysiological propertiesMethods:32 mongrel dogs were randomly divided into three groups, the low-dose group (n= 12), high-dose group (n= 12) and control group (n= 8). Three groups were all ligating the first diagonal branch of the left anterior descending coronary artery (LAD) to establish the canine model of acute myocardial infarction. After ligation the low-dose group was gived metoprolol 0.6mg/kg immediately by intravenous injection, the high-dose group was given 1.6mg/kg, while the control group was injected with same dose normal saline. Norepinephrine (NE) and epinephrine(E) levels in the coronary sinus (CS) blood, the ventricular effective refractory period (ERP) were all measured during the experiments.The incidence of VA was monitored among both groups. The pathological detection of infarction and infarct area were also performed then. Results were shown by x±s, NE and E changes were test by independent-samples T test. ERP changes were tested by paired t test, pairwise comparisons between different regions were calculated by LSD method, arrhythmia induced rates were compared by chi-square test.p<0.05 was considered statistically significance. All statistical analyzes were performed by SPSS 21.0 software.Results:1. The NE and E concentrations in three groups were all increased comparing with the previous measurement before ligation (NE:Control group 589.7±14.6ng/L vs 199.5± 27.4ng/L, p<0.05;Low-dose group 396.6±68.8 ng/L vs 192.3±17.4 ng/L, p<0.05; High-dose group,422.8±26.1 ng/L vs 201.8±27.8ng/L, p<0.05); Changes in the control group was the biggest increase compared with the other two groups(NE variation values: control group 390.18±26.9ng/L vs low-dose group 204.25±73.2 ng/L, the high-dose group 220.99±38.0 ng/L, p<0.05);The low-dose and high-dose group performs no significant difference,(204.25±73.2 ng/L vs 220.99±38.0 ng/L, p> 0.05);2. ERP values after myocardial infarction were significantly shorter in all three groups compared with the first mesurements,(Control group,137.5±1.2ms vs 154.9±0.8ms,p<0.05, Low-dose group,139.2±1.0ms vs 153.9±1.0ms,p<0.05, High-dose group 139.0±1.2ms vs 154.2±1.5 ms,p<0.05); The low-dose group and high dose group shortened ERP approximately,there was no statistically significance,(14.7±1.4ms vs 15.2±1.3 ms, p>0.05); Three groups all exhibited uneven shortness of ERP among different regions,infarct area was significantly shortened (p<0.05);3. In control group there was 4 dogs (50%, n=8) induced polymorphic ventricular tachycardia or ventricular fibrillation,the low-dose group had 5 dogs (41.7%,n=12) induced polymorphic ventricular tachycardia or ventricular fibrillation,the high-dose group had 4 dogs (33.3%,n=12).There was no significant difference among all groups (p>0.05);4. Pathology in all groups showed regional myocardial infarction changes such as dark red myocardium, coagulation necrosis, edema, hemorrhage and neutrophil infiltration.TH staining showed the injured sympathetic fibers.GAP43 staining did not see a positive result, failed to observe the effects on regeneration of sympathetic nerve fibers.Conclusion:Low and high dose of metoprolol performed similarly in reducing the catecholamine concentrations in dogs with anterior myocardial infarction,the same effects also observed in the reduction of regional ERP, but there was no differences in induced rrhythmias. |
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