Introduction: Boston Scientific’s VessixTM Over-the-Wire (OTW) balloon catheter uses bipolar radiofrequency (RF) energy and blood flow control to deliver significantly less energy than monopolar RF renal denervation systems. We hypothesize that the greater energy used in monopolar RF systems increases the risk for non-target tissue injury and inconsistent lumenal lesion formation.
Methods: A computational model was used to simulate the clinical settings and control algorithms of a monopolar single point catheter and bipolar balloon catheter. The electrical field was solved to calculate the Joule heating in tissue and a transient thermal model was solved for the temperature change for the duration of RF energy delivery.
In a swine model, RF treated renal arteries and select psoas muscles were rinsed and submerged in a beaker containing TTC (Triphenyl Tetrazolium Chloride) solution to aide in identification of thermal lesions. Non-viable tissue does not metabolize the stain and remains white, in contrast to red stained viable tissue.
Results: The computational model predicted that the monopolar RF lesion varied due to electrode-tissue contact conditions. Lesion depth was dependent on the electrical conductivity of the artery wall and structures near the electrode. In contrast, the Vessix bipolar balloon produced consistent lesion pattern and depth due to fixed balloon apposition and blood flow control, focal energy delivery, and the temperature control algorithm.
TTC stained renal arteries treated with the bipolar balloon device had accurate & consistent electrode placement. The single electrode monopolar device had inconsistent tip placement, with lesion depths decreasing with decreasing treatment time. Non-target lesions (psoas muscle and bowel) were observed with the monopolar device. Psoas muscle thermal lesion depth decreased from 1.5mm with 120s ablation time (67% incidence) to 0.3mm with 30s ablation time (17% incidence) with a single electrode unipolar device (N=16). Non-target lesions were not observed with the bipolar balloon device (N=13).
Conclusions: The BSC bipolar balloon renal denervation system had increased accuracy of electrode placement in the renal artery with no observations of non-target thermal injury.