Defining the Parameters for Endovenous Microwave Ablation to Achieve Equivalence With Endovenous Laser Ablation, Using the Porcine Liver Model

Aims Endovenous microwave ablation (EMWA) is an endovenous thermoablation (EVTA) system to ablate incompetent truncal veins. Early results suggest that EMWA uses more power than endovenous laser ablation (EVLA) to get the same results. We aimed to define the parameters for EMWA, which give the same tissue ablation as EVLA, using the validated porcine liver model. Methods EVLA (1470 nm 600 micron radial fibre) treatments were performed at 6 W, 8 W and 10 W, at pullback speeds of 6, 7, 8 and 9 s/cm, giving Linear Endovenous Energy Densities (LEEDs) between 36 - 90 J/cm. Each combination of power and pullback was repeated 5 times. We then used EMWA in the same model. Powers of 35-75 W and pullback speeds of 4-9 s/cm were used (LEEDs 140-675 J/cm). Ablation tracts from both devices were analysed by 2 blinded observers, noting thermal spread and carbonisation. Results For each commonly used parameter for EVLA, we identified a range of parameters for EMWA that produced similar tissue ablation in the porcine liver model. To keep the pullback speeds within the usual range, powers of 35-75 W were needed with EMWA, with mean EMWA LEEDs 3.9 - 5.8 times higher than EVLA LEEDs. We found the quicker the pullback speed, the higher the multiple of EMWA LEED we needed to get the same effect. Conclusion We have identified parameters for EMWA that gave equivalent tissue ablation in the porcine liver model to commonly used parameters used for EVLA. These need to be validated clinically, but as the model used has already been validated against clinical outcome in endovenous thermal ablation, there is little reason to suspect that these results would not be valid. As the power during EMWA is higher than EVLA, EVMA LEEDs are approximately 4-6 times higher than EVLA LEEDs to achieve the same thermal effect on the tissues.