Post mortem study of the depth and circumferential location of sympathetic nerves in human renal arteries--implications for renal denervation catheter design.

Objectives: The aims of this study were to examine human renal arteries and to accurately characterize their sympathetic innervation and location using CD-56 immunohistochemistry stains to highlight Neural Cell Adhesion Molecules (N-CAM).

Background: Porcine models have often formed the basis for design of denervation technology, with only a limited number of human studies available to detail the complex microarray of renal sympathetic nerves.

Methods: Post-mortem renal arteries (N = 14) were harvested and prepared into three sections (proximal, mid, and distal), and then stained using Hematoxylin and Eosin, followed by immunohistochemistry to characterize the expression of CD-56 renal neural tissue. Digital micro calipers were then used to measure the nerve distances and locations within the vessels.

Results: (i) Approximately 77% of nerves are located between 0.5 and 2.5 mm from the tunica intima layer, with 22.5% occurring in the 2.5-5.0 mm range, (ii) nerve bundles occur in 3-dimensional arborized arrays, (iii) the nerve bundles are evenly distributed throughout the proximal and distal vessel in this human study. Thickness of vessel wall correlated with proximity of the nerve bundles (r = 0.74, P < 0.01), and nerve bundle thickness (r = 0.62, P = 0.04). The larger the internal and external diameters and areas of the vessel were, the further the distance to the nearest nerve bundles were (r = 0.752, P =<0.01).

Conclusions: In human renal arteries with larger diameters and thicker vessel parenchyma, the innervation is found further from the lumen, and the nerves increase in thickness. This has implications for catheter and system design, as well as depth and duration of energy required for effective ablations. Effective percutaneous transluminal denervation procedures in this population would need to be circumferential rather than interrupted, and to mediate tissue damage to depths beyond 2.5 mm from the tunica intima.