In this issue of CRM, Petrov et al. have provided further evidence of the safety and efficacy of catheter-based renal denervation (RDN) for the treatment of poorly-controlled hypertension. These results support the concept that the completeness of the renal denervation plays an important role in achieving meaningful blood pressure (BP) lowering. Indeed, the results from their study suggest that with a monopolar catheter, with 20.4±3.9 ablations in the main and branch vessels in humans (“Y” technique), one can achieve substantial, and clinically meaningful, reductions in office and ambulatory systolic BP.
The concept of main renal artery plus distal branch denervation using radiofrequency (RF) ablation is not new. This was inspired by limited human data and porcine data that was highlighted after the failure of the SYMPLICITY HTN 3 trial. These data, describing the spatial distribution of renal sympathetic nerves, demonstrated that a significant number of renal sympathetic nerve fibers were out of range for RF ablation in the main renal artery. As many as 50% of the sympathetic nerve fibers may reside at depths of greater than 3 mm from the intimal surface, particularly in the more proximal segments of the renal artery. A single RF ablation may also only ablate an arc of only ~30-400 in humans, further limiting the completeness of denervation when using less than 6-8 ablations per side, and requiring precise “spiral” electrode placement in all quadrants . These are limitations for RF technologies, whether they are spiral multi-electrode arrays, image guided, or even sensing and image guided, “smart” systems, etc. These observations suggested that successful, and more complete, denervation with RF catheters would likely require additional ablations in the branch vessels where the nerve fibers come closer to the intimal surface.
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