Defining the parameters for endovenous microwave ablation to achieve equivalence with endovenous laser ablation, using the porcine liver model.

ABSTRACT

Aims: Endovenous microwave ablation (EMWA) is a relatively new catheter-based 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. Therefore, we aimed to define the parameters for EMWA, which give the same tissue ablation as EVLA, using the previously validated porcine liver model.

Methods:  EVLA (1470nm and 600micron radial fibre) treatments were performed at 6W, 8W and 10W, at each pullback speed of 6, 7, 8 and 9 s/cm, giving a range of Linear Endovenous Energy Densities (LEEDs) between 36 – 90 J/cm. We repeated each combination of power and pullback five times. Following a preliminary screening process to identify parameters that gave similar results, we used EMWA in the same model. Powers of 35-75W and pullback speeds of 4-9 s/cm were used (LEEDs 140-675 J/cm). Ablation tracts from both devices were analysed by two blinded observers, noting thermal spread and carbonisation. 

Results: For each of the commonly used parameters for EVLA, we identified a range of power and pullback parameters for EMWA that produced similar tissue ablation in the porcine liver model. To keep the pullback speeds within the usual range, we used powers of 35-75W 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 validated porcine liver model to commonly used parameters and LEEDs for EVLA. 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.