不同时机轻度低温干预对心室纤颤兔复苏后心脏的影响

Effect of pre-arrest and post-arrest mild hypothermia on myocardial function of ventricular fibrillation after restoration of spontaneous circulation in rabbits

目的：探讨轻度低温干预及其时机对心室纤颤（室颤）兔心功能、心肌超微结构和心肌细胞凋亡的影响。方法按随机数字表法将62只雄性新西兰兔分为常温对照组（n＝10）、低温对照组（n＝10）、常温复苏组（n＝14）、致颤前低温组（n＝14）、复苏后低温组（n＝14）5组。常温控制在（39.0±0.5）℃，低温控制在（33.5±0.5）℃。采用心外膜电刺激致颤法制备兔心肺复苏（CPR）模型，各组动物均持续监测4 h血流动力学指标，包括心率（HR）、左室收缩期末压（LVESP）、左室舒张期末压（LVEDP）、左室内压上升或下降最大速率（±dp/dt max）、平均动脉压（MAP）；低温各组均持续控温4 h后自然复温。复苏后48 h处死存活动物取左室心尖组织，电镜下观察心肌超微结构；采用原位末端缺刻标记法（TUNEL）观察细胞凋亡情况并计算凋亡指数（AI）。结果①复苏情况：致颤前低温组、复苏后低温组和常温复苏组间自主循环恢复率（ROSC）、CPR时间和总除颤能量差异均无统计学意义〔ROSC率：85.71%、71.43%、71.43%，CPR时间（s）：45.3±30.2、61.2±41.3、82.3±63.8，总除颤能量（J）：14.3±8.9、22.0±15.5、25.0±15.8，均P＞0.05〕。②血流动力学：各低温干预组观察期间HR均低于常温组（均P＜0.05）。致颤前低温组LVESP（mmHg，1 mmHg＝0.133 kPa）于0.5、1、2、3 h时显著高于常温复苏组（0.5 h：103.8±14.3比91.6±13.3，1 h：107.2±14.1比82.7±8.5，2 h：109.0±16.9比88.8±12.9，3 h：109.1±14.6比89.3±14.3，均P＜0.05）；LVEDP（mmHg）于0.5 h时显著低于常温复苏组和复苏后低温组（3.70±0.85比7.61±2.73、7.02±3.12，均P＜0.05），于1 h时显著低于常温复苏组（4.34±1.44比6.99±1.96，P＜0.05）；＋dp/dt max（mmHg/s）于1 h、2 h明显高于常温复苏组和复苏后低温组（1 h：2759.5±321.6比2123.0±304.5、2283.7±234.2，2 h：2730.6±425.1比2221.5±392.9、2252.6±476.0，均P＜0.05）。3个复苏组-dp/dt max和MAP各时间点差异均无统计学意义。③常温复苏组、致颤前低温组、复苏后低温组动物48 h存活率分别为60%、75%、100%，复苏后低温组显著高于常温复苏组（P＜0.05）。④致颤前低温组和复苏后低温组48 h后心肌超微结构损害和凋亡情况均较常温复苏组减轻，AI明显下降〔（28.05±9.82）%、（26.39±8.98）%比（42.02±13.36）%，均P＜0.05〕。结论轻度低温干预不影响ROSC率；致颤前轻度低温可以改善兔ROSC早期心肌收缩功能且对舒张功能无负性影响；复苏后轻度低温对心功能无明显抑制，并且可提高室颤兔48 h存活率；致颤前和复苏后轻度低温干预均可减少心肌细胞线粒体破坏和细胞凋亡，从而减少心功能损伤。

ObjectiveTo study the effect of pre-arrest and post-arrest mild hypothermia after restoration of spontaneous circulation （ROSC） on myocardial function, ultrastructure, apoptosis of myocardial cells in rabbits with ventricular fibrillation.Methods Sixty-two male New Zealand rabbits were randomly allocated into five groups： namely normothermic control group （NTC group,n = 10）, hypothermia control group （HTC group,n = 10）, normothermic resuscitation group （NTR group,n = 14）, hypothermia pre-arrest group （HPRA group,n = 14）, and hypothermia post-arrest group （HPOA group,n = 14）. The normal temperature was controlled at （39.0±0.5）℃, and the hypothermia （33.5±0.5）℃. Ventricular fibrillation cardiac arrest （CA） was reproduced in rabbits by transcutaneous epicardium electrical stimulation. The parameters of hemodynamics were monitored dynamically for 4 hours in all the groups, including heart rate （HR）, left ventricular end diastolic and systolic pressure （LVEDP/LVESP）, maximal rate of increase/decrease in left ventricular pressure （±dp/dt max）, and mean arterial pressure （MAP）. The body temperature of rabbits in hypothermia groups was maintained by surface cooling for 4 hours followed by rewarming. The survived rabbits were sacrificed at 48 hours after resuscitation, and myocardial apical tissue was harvested for observation of ultrastructure with electronic microscope, and to observe apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling （TUNEL） staining.Results① Resuscitation investigation： there was no significant difference in rate of ROSC, time of CPR and energy of defibrillation among HPRA, HPOA, and NTR groups [rate of ROSC： 85.71%, 71.43%, 71.43%; time of CPR （seconds）： 45.3±30.2, 61.2±41.3, 82.3±63.8;energy of defibrillation （J）： 14.3±8.9, 22.0±15.5, 25.0±15.8, allP〉 0.05].② Hemodynamics： compared with normal temperature groups, animals in hypothermia groups exhibited lower levels of HR （allP〈 0.05）. Compared with NTR group, HPRA group exhibited higher levels of LVESP （mmHg, 1 mmHg = 0.133 kPa） at 0.5, 1, 2 and 3 hours post ROSC （0.5 hour： 103.8±14.3 vs. 91.6±13.3, 1 hour： 107.2±14.1 vs. 82.7±8.5, 2 hours： 109.0±16.9 vs. 88.8±12.9, 3 hours： 109.1±14.6 vs. 89.3±14.3, allP〈 0.05）. Compared with NTR group and HPOA group, HPRA group exhibited lower levels of LVEDP （mmHg） at 0.5 hour post ROSC （3.70±0.85 vs. 7.61±2.73, 7.02±3.12, both P〈 0.05）. Compared with NTR group, HPRA group exhibited lower levels of LVEDP at 1 hour post ROSC （4.34±1.44 vs. 6.99±1.96,P〈 0.05）. In HPRA group, the level of＋dp/dt max （mmHg/s） was higher than that of NTR group and HPOA group at 1 hour and 2 hours post ROSC （1 hour： 2 759.5±321.6 vs. 2 123.0±304.5, 2 283.7±234.2, 2 hours：2 730.6±425.1 vs. 2 221.5±392.9, 2 252.6±476.0, allP〈 0.05）. There were no significant differences in -dp/dt max and MAP levels among three CPR groups.③ The survival rate at 48 hours post ROSC of NTR, HPRA and HPOA groups was 60%, 75%, and 100%, respectively. Compared with NTR group, higher survival rate was found in HPOA group at 48 hour post ROSC （P〈 0.05）.④ Compared with NTR group, less damage to myocardial ultrastructure was found in HPRA and HPOA groups. Apoptosis index （AI） was lower in HPRA and HPOA groups than that in NTR group [（28.05±9.82） %, （26.39±8.98） % vs. （42.02±13.36） %, bothP〈 0.05].Conclusions Our study shows that mild hypothermia has no effect on ROSC rate. Pre-arrest hypothermia can ameliorate myocardial systolic function of rabbit in early stage after ROSC, and it has no negative influence on diastolic function. Post-arrest mild hypothermia produces no negative influence on myocardial function of rabbit, but it improves 48 hours survival rate in ROSC rabbits. Both pre-arrest and post-arrest mild hypothermia therapy can attenuate myocardial injury in CA model of rabbits by ameliorating mitochondrial injuries and suppressing apoptosis of myocardial cells.