Catheter-based intravascular renal denervation (RD) using radiofrequency energy has shown promise in the treatment of resistant hypertension. However, to date, no studies have examined the extent of renal nerve injury following RD.

To examine renal nerve injury following RD, nine obese, hypertensive dogs underwent bilateral RD using the St. Jude Medical EnligHTN™ renal denervation system and eight weeks of hemodynamic monitoring. At the end of the eight-week period, both left and right renal arteries were collected from the aorta to the kidneys. The renal arteries were cut into equal sections, fixed, and embedded in paraffin. Multiple five-micron sections were taken from the bifurcation, main renal artery, and the ostium and stained with hematoxylin-eosin. Sections were examined for the total number of nerves, number of injured nerves, and the distance measured from nerves to the renal artery lumen.

Renal nerves were found from 0.28 mm to 6.7 mm from the renal artery lumen. Twelve percent of the nerves were found between 0.28mm and 1mm from the artery lumen, fifty-seven percent between 1mm and 2.5 mm, seventeen percent between 2.5mm and 3.5mm, and fourteen percent between 3.5mm and 6.7mm. Forty-two percent of nerves exhibited injury due to RD (157 out of 371); however, since samples were examined 8 weeks after RD, some injured nerves may have degenerated and become unobservable. Injury was found at nearly all distances from the artery lumen but was most prevalent from 0.28mm to 3.5mm. Renal nerve injury was found in thirty-six percent of the nerves near the bifurcation, forty-one percent in the main renal artery, and fifty-six percent near the ostium.

Our data show that renal nerves span a great distance from the renal artery lumen in obese canines. These data also suggest that the RD travels approximately 3.5mm from the artery lumen surface in obese dogs; however, renal nerve injury is noted further out. The injury further from the luminal surface is presumably the result of Wallerian-type degeneration. The current study showed that RD using the St. Jude Medical EnligHTN™ renal denervation system does cause significant injury to renal nerves.