Wittkampf Fred H M, Nakagawa Hiroshi
Heart Lung Center, Utrecht, The Netherlands.
Pacing Clin Electrophysiol. 2006 Nov;29(11):1285-97. doi: 10.1111/j.1540-8159.2006.00533.x.
The present treatment of atrial fibrillation by radiofrequency catheter ablation requires long continuous lesions in the thin walled left atrium where side effects may lead to serious complications. Better understanding of the physical processes that take place during ablation may help to improve the quality, safety, and outcome of these procedures. These processes include the distribution of power between blood, tissue, and patient; the mechanisms of tissue heating and coagulum formation; the relation between tissue and electrode temperatures; and the effects of increased electrode size and internal and external electrode cooling. With normal electrode-tissue contact, only a fraction of all power is effectively delivered to the tissue. Due to the variability of blood flow cooling, applied power and electrode temperature rise are poor indicators of lesion formation. With a longer electrode, the efficiency of tissue heating is decreased and the greater variation in tissue contact caused by electrode orientation makes lesion formation even more unpredictable. The absence of impedance rise during ablation does not guarantee the absence of blood clot formation on the tissue contact site. Blood clots may unnoticeably be created on the lesion surface and are caused by thermal denaturization of blood proteins, independent of heparinization. Irrigated ablation with external flush may prevent blood clot formation. Irrigation minimally affects lesion size by cooling the tissue surface. Larger lesions may only be created by the application of higher power levels. Electrode cooling, however, impedes electrode temperature feed back and blinds the operator for excessive tissue heating. External cooling alone with preservation of temperature feed back is a promising concept that may lead to improved procedural safety and success.
目前通过射频导管消融治疗心房颤动需要在薄壁的左心房形成长的连续损伤灶，而在此处副作用可能会导致严重并发症。更好地理解消融过程中发生的物理过程可能有助于提高这些手术的质量、安全性和疗效。这些过程包括血液、组织和患者之间的功率分布；组织加热和凝块形成的机制；组织温度与电极温度之间的关系；以及电极尺寸增大和电极内部及外部冷却的影响。在电极与组织正常接触的情况下，所有功率中只有一小部分能有效地传递到组织。由于血流冷却的变异性，施加的功率和电极温度升高并不是损伤灶形成的良好指标。使用较长的电极时，组织加热效率会降低，并且电极方向导致的组织接触变化更大，使得损伤灶形成更加不可预测。消融过程中阻抗没有升高并不能保证组织接触部位不会形成血凝块。血凝块可能在损伤灶表面悄然形成，并且是由血液蛋白的热变性引起的，与肝素化无关。外部冲洗的灌注消融可能会防止血凝块形成。冲洗通过冷却组织表面对损伤灶大小的影响最小。只有通过施加更高的功率水平才能形成更大的损伤灶。然而，电极冷却会妨碍电极温度反馈，并使操作人员无法察觉组织过度加热。仅进行外部冷却并保留温度反馈是一个有前景的概念，可能会提高手术的安全性和成功率。
