特定长脉冲超声新条件下适宜微泡“瀑布空化”效应治疗心肌无复流现象的实验研究

In up to 30% of cases of acute myocardial infarction, epicardial recanalization does not achieve optimal perfusion of the myocardial microvasculature even after successful percutaneous coronary intervention, a phenomenon known as “no-reflow”. Patients with no-reflow are associated with higher incidence of malignant arrhythmia, refractory heart failure, progressive left ventricular remodeling and significantly worse clinical outcomes. Therefore, how to give adequate and effective treatment to myocardium with no-reflow, is a very important issue of clinical significance. . Previously ultrasound (US) mediated microbubble (MB) cavitation effects have been shown to restore perfusion in myocardial infarction (sonothrombolysis). Traditionally it’s believed that MBs under high acoustic pressure do not persist after long acoustic cycles, therefore, most schemes of US-assisted therapy utilize a very short US pulse (a few acoustic cycles) when a high US pressure is used. We used an Ultra-high speed imaging system, which is capable of capturing up to 25 million frames per second (Mfps), to optically observe MB behaviors. It was shown that during long US tone burst excitation MBs first underwent inertial cavitation then formed gas-filled aggregates. MB aggregates continued to oscillate, break up, and more daughter bubbles were formed, eventually a phenomenon named as “cavitation cascade” or “caviation recycling”. We for the first time found that greater than 1000 cycles long pulsed US mediated MB destruction achieved successful microthrombi dissolution in vitro. More rapid and complete lysis was found when higher acoustic pressure and longer pulse length were utilized. Inertial cavitation played an important role in US-enhanced MB-mediated clot dissolution and may be monitored to evaluate the efficacy of thrombolytic treatment. . However, the exact mechanism of sonothrombolysis by MB cavitation remains unclear. Is there an etiologic relationship between improvement of microcirculation and MB cavitation cascade? How to safely quantify cavitation cascade to obtain an optimal sonothrombolysis effect? . In this study, we hypothesize that long pulsed US mediated MB “cavitation cascade” effects can be used for the treatment of myocardial no-reflow. Myocardial contrast echocardiography and fractional flow reserve techniques will be utilized for the assessment of MB cavitaiton effects on microvasular beds. In addition, the myocardial no-reflow tissue samples will be collected for the subsequent pathology analysis. We hope to find a new and powerful approach to overcome no-reflow phenomenon characterized by microvascular dysfunction.

约30%急性心肌梗死患者，即使通过支架术及时开通梗塞相关血管，但缺血区心肌的微血管床仍得不到充分的血流再灌注（无复流现象），严重影响了其预后。既往认为微泡在高声场作用下发生惯性空化后迅速消失，但我们用观察量程短至40钠秒的超高速成像系统发现，如果使用特定长脉冲超声来触发，微泡在发生惯性空化后继续形成气体聚合物持续震荡，最终生成众多子微泡触发持续的瀑布空化效应。并且我们通过空化信号监测，对瀑布空化效应信号实施了时间－频率量化分析。进一步实验显示，特定长脉冲超声联合微泡具有良好的溶解微血栓、改善微循环栓塞的效果，能改善急性大鼠下肢缺血骨骼肌微循环的血流灌注。我们假设长脉冲超声下微泡瀑布空化效应能够治疗心肌无复流现象，并使用心肌声学造影、分值血流储备等方法研究其对犬无复流模型的疗效，同时通过空化效应信号分析进一步探讨其机制，旨在为临床防治心肌无复流提供实验依据，为冠脉微循环障碍的治疗提供新方法。

约30%急性心肌梗死患者，即使通过支架术及时开通梗塞相关血管，但缺血区心肌的微血管床仍得不到充分的血流再灌注（无复流现象），严重影响了其预后。既往认为微泡在高声场作用下发生惯性空化后迅速消失，但我们用观察量程短至40钠秒的超高速成像系统发现，如果使用特定长脉冲超声来触发，微泡在发生惯性空化后继续形成气体聚合物持续震荡，最终生成众多子微泡触发持续的瀑布空化效应。并且我们通过空化信号监测，对瀑布空化效应信号实施了时间－频率量化分析。进一步实验显示，特定长脉冲超声联合微泡具有良好的溶解微血栓、改善微循环栓塞的效果，我们制备在体微动脉血栓栓塞模型，并且验证了长脉冲治疗超声联合微泡对微循环栓塞具有良好的治疗效果。使用2×106 MB/ml 的脂质体外壳微泡，在驱动频率1 MHz、声压1.8 MPa、脉冲重复频率 0.33 S-1的参数下，微泡的惯性空化效应随着脉冲长度的增加而增强，脉冲越长，引起的溶栓效果越好，微循环的血流恢复效果越佳。其中1000和5000Cycle的效果最佳，而特长脉冲（50,000Cycle）并未导致疗效的进一步提升。提示长脉冲超声的溶栓效果可能只在一定范围的周期内有效，过度的延长脉冲周期不会增加超声微泡的溶栓效果，反而造成微循环组织的出血和损伤等。这可能特长脉冲超声产生的热效应、过强的空化效应有关，提示我们需要控制空化效应使其适宜化以避免其潜在的有害作用。下一步实验可以进一步探究引起溶栓效应但无明显副作用的最适脉冲周期（以在1000周期左右为宜）。并且我们证明了长脉冲超声新条件下触发的微泡“瀑布空化”效应是其在体外产生作用的重要机制。长脉冲治疗组均可见到明显的惯性空化效应信号，且惯性空化效应持续的时间和强度随着脉冲的延长而增加。5000 周期组微泡的惯性空化强度最强，同时持续的时限也最长，超过了3 ms。而对照组未见类似的惯性空化信号产生。通过本实验对长脉冲超声的探索研究，为微循环障碍的治疗提供了实验依据和新的方法。