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.