Local and systemic effects of hepatic radiofrequency ablation in animal models
Radiofrequency ablation (RFA) is one of the latest developed thermal ablation for unresectable liver tumors. Despite the safety and high tumor ablation rate of RF A, there are grey areas in its clinical application that need to be further investigated. The objectives of the present study are to determine the local and systemic effects of hepatic RFA in animal models. It comprised ex-vivo and in-vivo experiments using porcine and rat models. The morphological characteristics of RF A zones and the local effect of RF A on the adjacent main portal vein (PV) branch were evaluated in the first part of the study. The second part of the study focused on the systemic inflammatory responses of hepatic RF A and the maximal host tolerance to large-volume hepatic RF A.
The minimal transverse diameter and volume of the ablated zone correlated positively with the exposed length of the electrode, the duration of ablation and the use of clustered electrode. Moreover, the deep margin of ablation extended 0.5 cm beyond the tip of the electrode, irrespective of different conditions of ablation. By qualitative and quantitative measures, there were non-viable hepatocytes from the center up to the margins of ablation of each RF A zone. These findings suggested that the electrode should be advanced through the target lesion for at least 0.5 cm beyond its deep margin so that a l-cm complete margin of ablation could be achieved.
The RF A procedure could be safely performed close to the main PV branch without Pringle maneuver and there was complete cellular destruction around the PV branch. Nevertheless, delayed manifestation of PV thrombosis and thermal injury to the hepatic artery and bile duct were observed if the RF A procedure was performed using Pringle
maneuver. Hence, Pringle maneuver might be dangerous during RFA for a liver tumor close to the main PV branch.
The hepatic RFA procedure of 30% - 35% of the whole liver volume was shown to be associated with less severe systemic inflammatory responses than hepatic cryotherapy of the same liver volume. Lung parenchyma and coagulation cascade were the main organs affected by these procedures. Besides, there was a threshold on the host tolerance to large-volume hepatic RF A, probably due to the systemic inflammatory reactions. Rats with normal liver could maximally tolerate RF A of 40% liver volume and those with cirrhotic liver could only tolerate RF A of 20% liver volume. Beyond that limit, the mortality rate was high up to 100%. These findings provided useful guidance on the aggressiveness of hepatic RF A treatment in clinical practice. Although the reported morbidity and mortality rates of RF A were low in clinical series, caution should be taken when large-volume RF A treatment was performed in patients with liver tumors.
Various local and systemic effects of hepatic RF A with clinical significance were evaluated in the present study. By careful application of this information in the clinical settings, the present results of RF A for liver tumors could be further improved.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:cancer thermotherapy catheter ablation rats as laboratory animals
Date of Publication:01/01/2004