Failure mechanisms in off-label electrosurgery devices for BASILICA, LAMPOON, and SESAME

Abstract

Background

Transcatheter electrosurgery using off-label guidewire-catheter systems to traverse or lacerate tissue may fail unexpectedly or cause non-target heating.

Objectives

To identify mechanisms of energy loss and non-target heating in off-label transcatheter electrosurgery systems.

Methods

We simulated electrosurgical traversal and Flying-V laceration used in BASILICA, LAMPOON, and SESAME in a 2-compartment benchtop model. We measured current distribution and regional heating in metallic-braided and non-metallic catheter assemblies.

Results

Longer, higher-power energy applications caused substantial catheter shaft heating and diverted energy delivery away from traversal or laceration targets. This reflected coupling between the guidewire and metallic catheter components and was amplified by thermal damage to insulation. Shorter, lower-power applications and non-metallic catheters reduced these effects.

In SESAME, the risk of dangerous intramyocardial heating was reduced by connecting the intracavitary limb of the Flying-V to the electrosurgery generator, instead of the intramyocardial limb.

Conclusions

Metallic braiding in commonly used microcatheters can divert energy away from electrosurgical targets to catheter shafts and cause clinically important non-target heating. In this benchtop model, energy applications of ≤2s largely avoided these failure modes. Operators should favor non-metallic catheters when feasible, use the shortest effective energy applications, and in SESAME energize the intracavitary limb. Purpose-built electrosurgical devices may improve safety and reliability.

Central Illustration

Failure mechanisms in off-label transcatheter electrosurgery systems used in BASILICA, LAMPOON, and SESAME.

Background

Transcatheter electrosurgery creates a plasma to vaporize tissue within the blood space, typically to traverse or lacerate tissue(1,2). Common configurations include a straight guidewire tip to traverse tissue, or a Flying-V denuded inner-curvature leaflet laceration surface. Common applications include transcaval aortic access; BASILICA, LAMPOON, and ELASTA-clip heart valve leaflet modification procedures; and SESAME transcatheter myotomy. Because these procedures rely on commercially available devices used outside their intended purpose, energy delivery may be unpredictable and non-target heating may occur. Electrosurgical failure can be benign, such as failure to traverse the intended target, or can be life threatening, such as hemodynamic collapse from leaflet avulsion resulting from failed electrosurgical laceration(3), or explosive “steam pop” from bystander tissue heating(4).

We therefore used benchtop models of BASILICA, LAMPOON, and SESAME to identify mechanisms of failure and to define practical operating limits using off-label devices.

Methods

Materials

We used the Astato XS20 0.014” × 300-cm guidewire (Asahi). It has a polytetrafluoroethylene (PTFE)-coated shaft that provides incidental electrical insulation. Its distal 17 cm is not PTFE-coated; instead it has a hydrophilic coating that offers little electrical insulation. The distal coil is joined with low-melting-point solder.

We tested the following 0.014” metallic-braided microcatheters: Finecross MG (Terumo), CorsairPro XS (Asahi), Caravel (Asahi). We also tested the following 0.035” microcatheter: Navicross (Terumo) used in SESAME to insulate the intramyocardial limb while permitting flush.

We also tested 0.014” non-metallic control microcatheters: Quick-Cross (Philips), TrailBlazer Straight (Medtronic), custom polyetheretherketone tubing.

We tested a 6-F Vista Brite Tip guiding catheter, which contains metallic braiding and a PTFE liner. It was tested allowable for TELLTALE electrosurgery(5).

Two-compartment test system

We constructed a 2-compartment saline bath model to measure current delivered to the target separately from current lost to the catheter shaft [FIGURE 1]. Each saline bath had its own return electrode. The compartments were connected through hemostatic valves (Pinnacle, Terumo), with the test device positioned across the barrier so that only the guidewire tip or Flying-V entered one compartment, while the shaft and coaxial catheter assembly remained in the other. Wideband current probes (6585, Pearson Electronics) measured current returning from each compartment independently.

Figure 1. Testing Setup.

a) Top view schematic of two-compartment saline bath jig, which separates traversal tip or Flying-V from catheter shafts across an insulating barrier. The guidewires are connected to a timer-driven electrosurgical generator and current monitor to simulate the clinical procedures. The red box indicates the view of infra-red camera pictures shown in figures 2–5.

b-d) Schematics of the three tested configurations: traversal, Flying-V leaflet laceration, and SESAME myotomy.

An electrosurgery generator (FT-10, Valleylab) was operated in monopolar pure-cut mode and connected to a timer to ensure consistent energy duration. Electrical isolation between compartments was confirmed before each measurement.

Thermography

Fiberoptic temperature measurements were unreliable because of electromagnetic interference and fluid motion. We therefore used infra-red thermography (E63900, FLIR) to assess relative heat accumulation along device tips and shafts. Devices were positioned just below the saline surface because water attenuates infra-red light. This method visualized relative heating patterns but did not provide absolute temperature measurements. A known limitation of infra-red thermography in fluid is that heated water disperses convectively and may misrepresent the heating source.

Leaflet traversal model

To simulate leaflet traversal, the guidewire tip extended 1mm beyond the selected 0.014” microcatheter [FIGURE 2a]. The coaxial guiding catheter tip overlapped the microcatheter tip. A 10mm proximal segment of guidewire was denuded to permit electrical connection.

Figure 2. Simulated leaflet traversal (for BASILICA or LAMPOON).

a) Schematic of a 0.014″ guidewire within a microcatheter and guiding catheter. An insulating barrier (dashed white line) separates the tip and shaft compartments. The red box indicates the physical layout of devices depicted on infra-red pictures.

b) Representative infra-red images showing heating at the tip versus shaft for metallic (CorsairProXS) and nonmetallic (Quick-Cross) microcatheters under short-duration low-power and long-duration high-power conditions. “Cold” microcatheter position is seen as grey silhouettes in infra-red images. With longer higher-power applications, the metallic microcatheter heats (yellow dotted arrow), whereas the non-metallic microcatheter does not.

c) Relative tip and shaft current in histograms. Most current reaches the tip (green bar) at low energy conditions; most current is diverted to the shaft and wasted (red bar) at high energy conditions.

d) Microscopic pictures of damaged microcatheter and guidewire tip, including melted solder (red arrows) and catheter polymers (blue arrows).

Flying-V leaflet laceration model

For simulated leaflet laceration, a 4mm segment on the inner curvature of the guidewire midpoint was denuded using a custom jig while preserving outer-curvature insulation, then bent sharply to create a tightly apposed Flying-V(3,6). One limb was covered by a 0.014” microcatheter and both limbs by guiding catheters [FIGURE 3a].

Figure 3. Simulated leaflet laceration (for BASILICA or LAMPOON).

a) The BASILICA/LAMPOON flying V configuration.

b, c) Representative infra-red images and current distribution plots show intended heat concentration at the Flying-V, irrespective of microcatheter design and applied energy conditions.

d) Micrographs show minimal insulation damage.

Flying-V SESAME myotomy model

For SESAME simulation, the Flying-V was prepared similarly. The simulated intramyocardial limb was covered with a Navicross 0.035” catheter passed through a more proximal guiding catheter, reproducing the clinical geometry of a basal septal guide catheter and more-apical Flying-V. The intracavitary limb was covered with a 0.014” microcatheter through an overlapping guiding catheter. [FIGURE 4a]

Figure 4. Simulated myotomy (for SESAME).

a) The SESAME Flying-V configuration.

b) Representative infra-red images compare highest effective energy settings (70W, 2s) versus excessive energy settings (70W, 3s). Most current reaches tip when energized for 2s, but most energy is diverted to shaft (red arrows) after 3s.

c) Relative tip and shaft histograms. Most current is diverted to shaft when energized for 3s. The metallic microcatheter accentuates this effect compared with the non-metallic microcatheter.

d) Minimal insulation damage after 2s. However after 3s, the outer curvature guidewire insulation is damaged (black arrow) and even the non-metallic microcatheter exhibits thermal injury (green arrow).

Which Flying-V limb to energize

Because only one Flying-V limb is connected to the generator during SESAME, we also tested a wire-only Flying-V without microcatheters. The intended current path is from generator to Flying-V and thereafter to the dispersive electrode. The disconnected/floating limb should not be part of the current path. We compared how current distribution and heating varied whether the intracavitary or the intramyocardial was energized, along with the impact of insulation defects.

Post-test inspection

After high-power testing, devices were examined microscopically for insulation disruption, polymer damage, and solder melting. Special attention was given to the outer curvature (“summit”) of the Flying-V.

Data sharing

Data are available at https://doi.org/10.25444/nhlbi.31566301 in accordance with NIH data sharing policy.

Results

Simulated leaflet traversal (for BASILICA or LAMPOON)

At low power and short duration, most applied current reached the guidewire tip regardless of microcatheter type [FIGURE 2]. Braided metallic and non-metallic microcatheters both adequately insulated the shaft under these conditions, and infra-red thermography showed heating localized near the guidewire tip.

At higher power and longer duration, much less current reached the guidewire tip and much more was diverted to the shaft. Thermography showed clear shaft heating, especially with braided metallic microcatheters. Non-metallic microcatheters reduced this effect but did not eliminate it, because of residual capacitive coupling(7).

Microscopy after testing showed polymer damage and solder melting, consistent with thermal injury and insulation failure.

These findings identified three mechanisms of guidewire energy loss: inductive coupling to metallic braid, conductive coupling after insulation failure, and capacitive coupling to surrounding media.

Simulated leaflet laceration (for BASILICA or LAMPOON)

In the BASILICA/LAMPOON Flying-V configuration [FIGURE 3], low-power short-duration applications directed most current to the intended laceration segment, with little shaft loss. At higher power and longer duration, current delivery to the Flying-V was better preserved than in the traversal model, likely because both limbs were insulated by guiding catheters. However, heating increased and post-test microscopy showed insulation injury at the outer curvature of the Flying-V and polymer damage to the catheter system. Thus, Flying-V laceration was less susceptible than traversal to severe shaft energy loss, but longer, higher-power applications still damaged the device and increased non-target heating.

Simulated myotomy (for SESAME)

At low power and short duration, current delivery in the SESAME configuration resembled the BASILICA/LAMPOON model, with relatively little shaft loss [FIGURE 4]. At higher power and longer duration, most applied energy was diverted to the shaft rather than delivered to the Flying-V. We measured induced voltage within metallic guiding catheter braid, confirming strong coupling between the energized wire and the guide catheter.

Heating within the guiding catheter lumen caused ejection of hot fluid or steam from the catheter tip. This effect persisted even with non-metallic microcatheters, implicating the guiding catheter itself as an important source of heating.

Practical energy limit

In this benchtop model, applications of 70W for ≤2s largely avoided insulation failure, conductive energy diversion, and major inductive energy loss, whereas longer applications caused abrupt worsening of these failure modes [FIGURE 4].

Which Flying-V limb to energize: intramyocardial versus intracavitary

Unintended heating of myocardial tissue is more consequential than heating of flowing anticoagulated blood within the LV cavity. We therefore tested whether bystander heating was affected by which Flying-V limb was energized by directly connecting to the electrosurgery generator.

In the wire-only Flying-V configuration, when insulation remained intact, heating was localized mainly to the denuded laceration surface and to the energized limb, with little heating along the disconnected “free” limb [FIGURE 5].

Figure 5. Which Flying-V limb to electrify: intramyocardial versus intracavitary.

a) Flying-V test configuration without microcatheters.

b) Intentional guidewire insulation fault (red arrow).

c) The energized limb (attached to the electrosurgery generator) heats (yellow arrow) whereas the disconnected limb does not, when the insulation remains intact.

d) With an (intentional) insulation fault on the energized limb (left), focal heating (red arrow) is worse than with an insulation fault on the disconnected limb (right). Yellow arrows depict diffuse heating of the energized limb.

e) Energized limbs heat diffusely (yellow arrows) and also focally at intentional insulation faults (red). Connecting both limbs to the electrosurgery generator (right-most) increases shaft heating.

Insulation defects can result from thermal disruption, or from mechanical disruption during normal use. When an intentional focal insulation defect was introduced on the energized limb, current was diverted through the defect and created a secondary thermal hotspot. When a defect was present on the disconnected limb, the defect could also permit unintended current flow and heating remote from the laceration surface.

These findings support connecting the generator to the intracavitary rather than the intramyocardial limb during SESAME to reduce the likelihood of unintended deep intramyocardial heating.

Discussion

This benchtop study shows that off-label transcatheter electrosurgery systems can fail in predictable ways [FIGURE Central Illustration]. The central mechanism is energy diversion away from the intended target. Instead of remaining confined to the guidewire tip during traversal or the Flying-V during laceration, current may be transferred to catheter shafts and surrounding fluid, reducing procedural effectiveness and increasing the risk of thermal injury.

Three mechanisms accounted for energy loss (Table 1). Conductive coupling occurred when the guidewire made direct electrical contact with metallic catheter components, usually after insulation had been disrupted by abrasion or heat. The Astato guidewire lacks distal PTFE insulation, and the inner liner of many microcatheters is designed primarily for lubricity rather than electrical insulation. Inductive coupling occurred when alternating current in the guidewire induced current in nearby metallic braiding, even without direct contact. The resulting heating could further damage polymer insulation and promote conductive coupling. Capacitive coupling occurred between the energized guidewire and surrounding blood and tissue even without direct metallic contact(7).

Table 1.

Summary of failure modes in transcatheter electrosurgery using off-label commercial devices.

Mechanism	Trigger	Effect
Conductive coupling	Missing or damaged insulation	Direct guidewire-to-metal contact diverts energy and causes focal heating
Inductive coupling	Adjacent metallic braid or coils	Alternating current in the guidewire induces current in metallic catheter components and heats the shaft
Capacitive coupling	Energized guidewire in conductive media	Energy dissipates into surrounding dielectric media despite intact insulation
Mechanical	Missing or damaged insulation	Dispersion of power away from intended target, short-circuit caused by abrasion, thermal injury, or off-label design

These findings have important practical implications for operators performing BASILICA, LAMPOON, SESAME, and related procedures using off-label devices.

First, operators should prefer non-metallic microcatheters when feasible because they reduce inductive and conductive coupling. Among the devices tested, Quick-Cross appeared least susceptible to metallic coupling.

Second, operators should use the shortest effective energy applications. Under the tested conditions, pulses of ≤2s at ≤70W largely avoided the failure modes seen with longer applications. Short pulses limited thermal damage, reduced insulation failure, and minimized shaft heating. Insulation damage to the outer curvature of the Flying-V undermines effectiveness of leaflet laceration. When high power is required, energy should be delivered in brief controlled bursts rather than prolonged continuous applications.

Third, in SESAME, the intracavitary limb (coiled distal AstatoXS tip) should preferentially be connected to the electrosurgery generator. The wire-only experiments showed that the energized limb bears the greater thermal burden. As long as there is no insulation fault, deep myocardial heating that risks life-threatening “steam pop” (4)is unlikely. Both Flying-V limbs should not be connected in parallel because this increases heated wire surface area and energy loss. In addition, during SESAME, guiding catheters should be positioned away from direct myocardial contact, and flushing during energy delivery may help dissipate heat and vent heated fluid.

The study highlights the fragility of off-label devices. We observed melting of low-melting-point guidewire solder and catheter polymers. These findings may inform the design of safer, more predictable purpose-built devices.

Limitations

This was an in vitro study. The model does not reproduce blood flow, tissue contact, cardiac motion, or the full thermal and electromagnetic conditions in vivo. Saline does not mimic blood or myocardium during heating. Infra-red thermography provided relative, not absolute, temperature information and was influenced by convective fluid motion. We tested a single electrosurgery generator, and other generators may behave differently because of different power-control algorithms(8,9). We tested microcatheters without metallic braiding, but we are not aware of commercially available guiding catheters that do not incorporate metallic braiding.

Conclusions

Off-label guidewire-catheter systems used for transcatheter electrosurgery can divert energy away from the intended target and cause clinically important non-target heating. Metallic braid and insulation failure are key contributors.

In this benchtop model, energy applications of ≤2s and ≤70W largely avoided these failure modes. Operators should favor non-metallic catheters when feasible, use the shortest effective energy applications, and in SESAME energize the intracavitary rather than the intramyocardial Flying-V limb. Purpose-built electrosurgical devices are needed to improve reliability and safety.

Clinical Perspectives.

What Is Known?

• Off-label transcatheter electrosurgery systems may deliver energy unpredictably and can cause non-target heating

What Is New?

• Longer higher-power energy application damages devices, diverts energy away from intended vaporization targets, and increases waste energy that causes non-target bystander heating.

• Application of energy pulses ≤2s averts important bystander heating.

• Non-metallic microcatheters exhibit less inductive and conductive coupling that cause heating.

• SESAME operators should energize the intracavitary limb to reduce dangerous myocardial heating.

What Is Next?

• Purpose-built electrosurgical devices are needed.

Abbreviations

BASILICA

Bioprosthetic or native Aortic Scallop Intentional Laceration to prevent Iatrogenic Coronary Artery obstruction

LAMPOON

Laceration of the Anterior Mitral leaflet to Prevent left ventricular Outflow tract ObstructioN

PTFE

Polytetrafluoroethylene

SESAME

Septal Scoring Along Midline Endocardium