Discussion
Tissue puncture using RF energy relies on transfer of alternating current to the target tissue to generate localized heating and tissue vaporization. Successful crossing requires focal delivery of current. The current density (rate of charge transfer per unit area) is dependent on the amount of delivered power and electrode size. Off-label application of electrocautery to metal guidewires during atrial septal puncture may lead to unintended damage to the dilator or guidewire itself with potential adverse clinical consequences. Firstly, electrified guidewires have an active electrode that is dependent on manual exposure of the wire from dilator (i.e. dilator-wire tip distance), which introduces uncertainty in the exact current density and, therefore, TSP effectiveness and consistency between cases. This may explain why more power was needed in the present study when using electrified guidewires compared to a dedicated RF wire. Additionally, electrified guidewires are typically coated with fluoropolymers and epoxy based hydrophilic coatings (such as polytetrafluoroethylene) for lubricity and electrical insulation, which has been suggested to be a source of current leakage along the entire length of the wire.29, 30 This not only impacts the effective current density and TSP effectiveness, but also poses electrosurgical safety risks for patients31-33 that can, otherwise, be mitigated by minimizing power34, 35 and using dedicated insulated tools.36, 37
The present study compared the safety and effectiveness of a dedicated RF wire to electrified guidewires using a range of power settings and dilator-wire tip distances. The RF wire with pre-set average power of 5W demonstrated 100% success at TSP. While higher power with electrified guidewires was expected to correlate with increased current density and tissue vaporization, electrified guidewires had lower effectiveness and greater variability in TSP success between samples than the dedicated RF wire. Increasing the power applied to electrified guidewires from 20W to 50W did not translate into a substantial improvement on TSP effectiveness, suggesting the current leakage along the length of the guidewire may reduce the effectiveness of RF delivery. The distance between the dilator and wire tip did not significantly impact TSP using the dedicated RF wire, but appeared to have an inverse effect on TSP success using electrified guidewires. However, a small dilator-wire tip length also correlated with damage to both the wire and dilator tip, presenting a risk of particle liberation and embolization. At the maximum dilator-wire distance tested (5mm), the 0.014” electrified guidewires required significantly more RF applications than the RF wire, and the 0.032” guidewires failed to perforate the septum. The discrete active electrode and insulated shaft of the dedicated RF wire may explain why TSP effectiveness was not sensitive to the distance between the dilator and wire, and why no damage was observed on the RF wire or its dedicated dilator.
Perforation of the atrial septum using a dedicated RF system has been previously shown to create a similar extent of tissue injury and healing as mechanical needle puncture.38 In the present study, electrified guidewires under all conditions led to larger tissue defects, evidence of tissue charring, and irregular morphology compared to the purpose-built RF system, suggesting a greater extent of tissue injury. Tissue charring has been correlated with thermal injury, destructive degeneration with amorphous or necrotic tissue,21, 39 and thrombus formation.40 Disruption of collagen and fibrous structures impact tissue elasticity21 and may present a risk of tearing or persistent atrial septal defects.41
The use of higher power presents greater risks of electrosurgical injury34, 35, 42 and thermal damage,43 as well as thrombus44 and coagulum formation.14, 45{Gowda, 2017 #17} Localized temperature measurements demonstrated higher core temperature and a visually larger area of tissue heating with use of electrified guidewires, as compared to the dedicated RF wire, which is consistent with the observed larger puncture defects, tissue charring and equipment deformation.
Overall findings suggest electrified guidewires create larger defects and are more sensitive to the distance between the tip of the wire and the tip of the dilator, which may be difficult to assess and control precisely in a clinical setting, thereby, causing uncertainty in TSP success and inconsistency between cases. Although the RF wire has a larger shaft diameter (0.035”) compared to the electrified guidewires used in this study (0.014” and 0.032”), the size of septal defects appeared to be smaller.