Department of Biomedical Engineering, Washington University in Saint Louis, MO 63130-4899, USA.
Circ Arrhythm Electrophysiol. 2012 Apr;5(2):409-16. doi: 10.1161/CIRCEP.111.967216. Epub 2012 Feb 9.
High intensity focused ultrasound (HIFU) has been introduced for treatment of cardiac arrhythmias because it offers the ability to create rapid tissue modification in confined volumes without directly contacting the myocardium. In spite of the benefits of HIFU, a number of limitations have been reported, which hindered its clinical adoption.
In this study, we used a multimodal approach to evaluate thermal and nonthermal effects of HIFU in cardiac ablation. We designed a computer controlled system capable of simultaneous fluorescence mapping and HIFU ablation. Using this system, linear lesions were created in isolated rabbit atria (n=6), and point lesions were created in the ventricles of whole-heart (n=6) preparations by applying HIFU at clinical doses (4-16 W). Additionally, we evaluate the gap size in ablation lines necessary for conduction in atrial preparations (n=4). The voltage sensitive dye di-4-ANEPPS was used to assess functional damage produced by HIFU. Optical coherence tomography and general histology were used to evaluate lesion extent. Conduction block was achieved in 1 (17%) of 6 atrial preparations with a single ablation line. Following 10 minutes of rest, 0 (0%) of 6 atrial preparations demonstrated sustained conduction block from a single ablation line. Tissue displacement of 1 to 3 mm was observed during HIFU application due to acoustic radiation force along the lesion line. Additionally, excessive acoustic pressure and high temperature from HIFU generated cavitation, causing macroscopic tissue damage. A minimum gap size of 1.5 mm was found to conduct electric activity.
This study identified 3 potential mechanisms responsible for the failure of HIFU ablation in cardiac tissues. Both acoustic radiation force and acoustic cavitation, in conjunction with inconsistent thermal deposition, can increase the risk of lesion discontinuity and result in gap sizes that promote ablation failure.
高强度聚焦超声（HIFU）已被引入治疗心律失常，因为它能够在不直接接触心肌的情况下在有限的体积内快速产生组织改性。尽管 HIFU 具有优势，但仍有许多局限性报告，这阻碍了其临床应用。
在这项研究中，我们使用了一种多模态方法来评估 HIFU 在心脏消融中的热和非热效应。我们设计了一个计算机控制系统，能够同时进行荧光映射和 HIFU 消融。使用该系统，在离体兔心房（n=6）中创建线性损伤，在全心（n=6）制备物的心室中创建点损伤，应用临床剂量（4-16 W）的 HIFU。此外，我们评估了心房制备物中传导所需的消融线的间隙大小（n=4）。电压敏感染料 di-4-ANEPPS 用于评估 HIFU 产生的功能损伤。光学相干断层扫描和一般组织学用于评估损伤程度。在 6 个心房制备物中，有 1 个（17%）通过单次消融线实现了传导阻滞。休息 10 分钟后，6 个心房制备物中没有 1 个（0%）通过单次消融线持续发生传导阻滞。由于沿损伤线的声辐射力，在 HIFU 应用过程中观察到 1 至 3 毫米的组织移位。此外，HIFU 产生的过高声压和高温会产生空化，导致宏观组织损伤。发现 1.5 毫米的最小间隙尺寸可传导电活动。
本研究确定了 3 种导致 HIFU 消融在心脏组织中失败的潜在机制。声辐射力和超声空化，加上不一致的热沉积，会增加损伤不连续性的风险，并导致促进消融失败的间隙尺寸。
