Patterson E J, Scudamore C H, Owen D A, Nagy A G, Buczkowski A K
Department of Surgery, Vancouver Hospital and Health Sciences Center, University of British Columbia, Canada.
Ann Surg. 1998 Apr;227(4):559-65. doi: 10.1097/00000658-199804000-00018.
To determine, in vivo, the effect of radiofrequency ablation (RFA) treatment time and tissue blood flow on the size and shape of the resulting necrotic lesion in porcine liver.
Radiofrequency ablation is an electrosurgical technique that uses a high frequency alternating current to heat tissues to the point of desiccation (thermal coagulation). Radiofrequency ablation is well established as the treatment of choice for many symptomatic cardiac arrhythmias because of its ability to create localized necrotic lesions in the cardiac conducting system. Until recently, a major limitation of RFA was the small lesion size created by this technique. Development of bipolar and multiple-electrode RFA probes has enabled the creation of larger lesions and therefore has expanded the potential clinical applications of RFA, which includes the treatment of liver tumors. A basic understanding of factors that influence RFA lesion size in vivo is critical to the success of this treatment modality. The optimal RFA technique, which maximizes liver lesion size, has yet to be determined. Theoretically, lesion size varies directly with time of application of the RF current, and inversely with blood flow, but these relationships have not been previously studied in the liver.
Six animals underwent hepatic RFA (460 kHz), for 5, 7.5, 10, 12.5, 15, and 20 minutes. Identical, predetermined anatomic areas of the liver were ablated in each animal. Two additional animals underwent 12 RFA treatments -- 6 with vascular inflow occlusion (Pringle maneuver) and 6 with uninterrupted hepatic blood flow. Animals were euthanized and the livers were removed for gross pathologic examination. All lesions were measured in three dimensions and photographed. Tissues were examined by routine histology and by histochemistry to determine viability.
Increasing duration of RFA application from 5 through 20 minutes did not create lesions of larger diameter, but this time increase did predict deeper lesion production (beta = 0.34, p = 0.04). A range of lesion shapes were created from four separate ovals (corresponding to each electrode), to larger ovals intersecting to form a cross, to spheroid lesions. The number of blood vessels in close proximity to the probe tip (within a 1-cm radius from the center of the lesion) strongly predicted minimum lesion diameter (beta = -0.61, p = 0.0001) and lesion volume (beta = -0.56, p = 0.0004). This negative effect of blood flow on lesion size was confirmed experimentally. Radiofrequency ablation lesions created during a Pringle maneuver were significantly larger in all three dimensions than lesions created without a Pringle maneuver: minimum diameter was 3.0 cm (with Pringle) versus 1.2 cm (p = 0.002), maximum diameter was 4.5 cm (with Pringle) versus 3.1 cm (p = 0.002), depth was 4.8 cm (with Pringle) versus 3.1 cm (p < 0.001), and lesion volume was 35.0 cm3 (with Pringle) versus 6.5 cm3 (p < 0.001).
Blood flow is a strong predictor of all RFA lesion dimensions in porcine liver in vivo, whereas a change of treatment time from 5 to 20 minutes is predictive only of lesion depth, but not diameter or volume.
在猪肝脏活体实验中，确定射频消融（RFA）治疗时间和组织血流对所形成坏死灶大小和形状的影响。
射频消融是一种电外科技术，利用高频交流电将组织加热至干燥（热凝固）点。由于射频消融能够在心脏传导系统中形成局部坏死灶，因此已成为许多有症状心律失常的首选治疗方法。直到最近，射频消融的一个主要局限性是该技术所形成的病灶较小。双极和多电极射频消融探头的开发使得能够形成更大的病灶，从而扩大了射频消融的潜在临床应用范围，其中包括肝肿瘤的治疗。深入了解影响活体射频消融病灶大小的因素对于这种治疗方式的成功至关重要。尚未确定能使肝脏病灶大小最大化的最佳射频消融技术。从理论上讲，病灶大小与射频电流施加时间成正比，与血流成反比，但此前尚未在肝脏中对这些关系进行研究。
对6只动物进行肝脏射频消融（460kHz），持续时间分别为5、7.5、10、12.5、15和20分钟。在每只动物的肝脏中，对相同的、预先确定的解剖区域进行消融。另外2只动物接受了12次射频消融治疗——6次在血管流入阻断（Pringle手法）下进行，6次在肝脏血流未中断的情况下进行。对动物实施安乐死后取出肝脏进行大体病理检查。对所有病灶进行三维测量并拍照。通过常规组织学和组织化学检查组织以确定其活力。
将射频消融的持续时间从5分钟增加到20分钟，并未形成直径更大的病灶，但这种时间增加确实预示着病灶会更深（β = 0.34，p = 0.04）。形成了一系列病灶形状，从四个独立的椭圆形（对应每个电极），到相交形成十字的较大椭圆形，再到球形病灶。紧邻探头尖端（在距病灶中心1厘米半径范围内）的血管数量强烈预示着最小病灶直径（β = -0.61，p = 0.0001）和病灶体积（β = -0.56，p = 0.0004）。血流对病灶大小的这种负面影响通过实验得到了证实。在Pringle手法下进行射频消融所形成病灶的所有三个维度均显著大于未采用Pringle手法所形成的病灶：最小直径为3.0厘米（采用Pringle手法）对1.2厘米（p = 0.002），最大直径为4.5厘米（采用Pringle手法）对3.1厘米（p = 0.002），深度为4.8厘米（采用Pringle手法）对3.1厘米（p < 0.001），病灶体积为35.0立方厘米（采用Pringle手法）对6.5立方厘米（p < 0.001）。
血流是猪肝脏活体中所有射频消融病灶维度的有力预测指标，而治疗时间从5分钟到20分钟的变化仅能预测病灶深度，而非直径或体积。
