Predictors of Thrombosis in Hepatic Vasculature during Microwave Tumor Ablation of an In Vivo Porcine Model

Abstract

Purpose The goal of this study was to evaluate and model the risk of in-vivo thrombosis in each hepatic vessel type during hepatic microwave ablation as a function of vessel diameter, velocity and vessel-antenna spacing. Materials and Methods A single microwave ablation antenna was inserted into a single porcine lobe (n=15 total) adjacent to a hepatic artery, hepatic vein, or portal vein branch. Conventional and Doppler ultrasound were used to measure the vessel diameter, blood flow velocity, and vessel-antenna spacing. A microwave ablation zone was then created at 100 W for 5 minutes. Thrombus formation was evaluated on immediate post-procedure ultrasound imaging. Logistic regression was used to evaluate the predictive value of vessel diameter, blood flow velocity and vessel-antenna spacing on vascular thrombosis. Results Thrombosis was identified in 53% of portal veins, 13% of hepatic veins and 0% of the hepatic arteries. The average peak blood flow rate of the hepatic artery was significantly greater than that of the hepatic vein and portal vein. Peak blood flow velocities less than 12.45 cm/sec, vessel diameters less than 5.10 mm and vessel-antenna spacings less than 3.75 mm were strong predictors of hepatic vein thrombosis. However, these individual factors were not predictive of the more common portal vein thrombosis. Conclusions Hepatic arteries do not appear to be at risk for thrombosis during microwave ablation procedures. Portal vein thrombosis was more common than hepatic vein thrombosis during microwave ablation treatments, but was not as predictable based upon vessel diameter, flow velocities, or vessel-antenna spacing alone.

Effects of Microwave Ablation on Arterial and Venous Vasculature after Treatment of Hepatocellular Carcinoma

“…Hepatic veins were found to be more resistant to occlusion, with vessels larger than 1.5 mm in diameter being relatively protected from occlusion. The increased rate of portal vein occlusion compared with hepatic vein occlusion within the ablation zone (39.7% vs 15.0%, respectively), with equivalent size distributions, is also similar to the results of previous in-vivo studies (19).…”

“…In conclusion, our study shows that, during microwave tumor ablation of HCC, hepatic veins and arteries are leading to fewer occlusions (19). Hepatic arteries, which were as resistant to occlusion as hepatic veins, are also characterized by high-flow velocity and pulsatility (24).…”

“…Determining which vessels are at risk for thrombosis during an ablation is essential to find a balance between treatment efficacy and safety, but not enough is known about how portal veins, hepatic veins, and hepatic arteries respond to ablation-induced thermal damage to guide treatments for either clinical goal. Previous studies showed that vessel size, vessel-antenna spacing, and hepatic vessel type are associated with vascular occlusion after thermal ablation (16)(17)(18)(19). However, these conclusions were derived from phantom or nontumor porcine liver models.…”

Microwave ablation in primary and secondary liver tumours: technical and clinical approaches

“…In vivo studies have shown that vessels smaller than 3 mm in diameter encompassed by the ablation zone are likely to thrombose during MW ablation (51). Additional pre-clinical studies suggest that hepatic arteries, which serve as the main blood supply to HCC, are less likely to thrombose due to their high flow states (52). …”

Potential Mechanisms of Vascular Thrombosis after Microwave Ablation in an in Vivo Liver

“…More recent studies have identified greater thrombosis rates in smaller portal veins compared to hepatic veins in both porcine and human livers (7,16). The purpose of this study was to evaluate potential mechanisms for the observed differences in thrombosis rates by quantifying thrombosis-related gene and protein expression in normal vessels as well as differences in heat transfer during the ablation procedure.…”