Aims: Trials of transcatheter renal artery denervation (RDN) have failed to show consistent antihypertensive
efficacy. Procedural factors and limitations of radiofrequency ablation can lead to incomplete
denervation. The aim of the study was to show that non-contact microwave catheter ablation could produce
deep circumferential perivascular heating while avoiding injury to the renal artery intima and media.
Methods and results: A novel microwave catheter was designed and tested in a renal artery model consisting
of layers of phantom materials embedded with a thermochromic liquid crystal sheet, colour range
50-78°C. Ablations were performed at 140 W for 180 sec and 120 W for 210 sec, delivering 25,200 J with
renal arterial flow at 0.5 L/min and 0.1 L/min. Transcatheter microwave ablations 100-160 W for 180 sec
were then performed in the renal arteries of five sheep. In vitro, ablations at 140 W and 0.5 L/min flow produced
circumferential lesions 5.9±0.2 mm deep and 19.2±1.5 mm long with subendothelial sparing depth
of 1.0±0.1 mm. In vivo, transcatheter microwave ablation was feasible with no collateral visceral thermal
injury. There was histological evidence of preferential outer media and adventitial ablation.
Conclusions: Transcatheter microwave ablation for RDN appears feasible and provides a heating pattern
that may enable more complete denervation while sparing the renal arterial intima and media.