Transcatheter Electrosurgery: JACC State-of-the-Art Review

Abstract

Transcatheter electrosurgery refers to a family of procedures using radiofrequency energy to vaporize and traverse or lacerate tissue despite flowing blood. We review theory, simulations, and benchtop demonstrations of how guidewires, insulation, adjunctive catheters, and dielectric medium interact. For tissue traversal, we insulate all but the tip of traversing guidewires to concentrate current. For leaflet laceration, the “Flying V” configuration concentrates current at the inner lacerating surface of a kinked guidewire. Flooding the field with non-ionic dextrose eliminates alternative current paths. Clinical applications include traversing occlusions (pulmonary atresia, arterial and venous occlusion, and iatrogenic graft occlusion), traversing tissue planes (atrial and ventricular septal puncture, radiofrequency valve repair, transcaval access, Potts and Glenn shunts), and leaflet laceration (BASILICA, LAMPOON, ELASTa-clip and others). We provide tips for optimizing these techniques. Transcatheter electrosurgery enables a range of novel therapeutic procedures for structural heart disease already, and represents a promising advance towards transcatheter surgery.

Condensed Abstract:

Transcatheter electrosurgery refers to a family of procedures using radiofrequency energy to vaporize and thereby traverse or lacerate tissue despite flowing blood. This review introduces basic electromagnetic principles and how they apply to tissue traversal and cutting. We review a range of clinical applications of transcatheter electrosurgery. These include traversing vascular and chamber occlusions, traversing tissue planes (atrial and ventricular septal puncture, radiofrequency valve repair, transcaval access, Potts and Glenn shunts), and leaflet laceration (BASILICA, LAMPOON, ELASTa-clip etc). Transcatheter electrosurgery enables a range of novel therapeutic procedures for structural heart disease already, and represents a promising advance towards transcatheter surgery.

Introduction

Transcatheter electrosurgery is a technique to traverse or cut tissue, typically within blood-filled spaces, using alternating current directed by guidewires and catheters. The technique has been applied to traverse occluded arterial and venous lesions, traverse between intact as well as atretic cardiac chambers, and more recently, to cut heart valve leaflets. Alternating current in the radiofrequency range (approximately 500KHz) is concentrated at the target tissue to heat and vaporize tissue, also called ‘cutting’ (1). Electrosurgery should not be confused with electrocautery. Electrosurgery relies on transfer of current to the target tissue where the increased current density generates heat and vaporization. Electrocautery relies on direct transfer of heat from a hot implement to tissue, typically to arrest bleeding. Furthermore, electrophysiological catheter ablation differs from transcatheter electrosurgery in that radiofrequency energy is used to form non-conductive lesions rather than to vaporize tissue.

Surgeons typically employ electrosurgery using an active electrode, the electrosurgery ‘pencil’, in a dry air-filled field and under direct operator vision. By contrast, transcatheter electrosurgery uses a long guidewire within conductive media (blood) and under fluoroscopic or echocardiographic guidance. This has important technical implications for charge concentration to achieve cutting, inadvertent charge dispersion that impedes cutting, electrode degradation through carbonization, and undesired blood coagulation.

This review explores the physics of transcatheter electrosurgery relevant to interventional physicians. It surveys commercially available and off-the-shelf equipment needed to deliver radiofrequency energy. It assesses contemporary applications of the technique. It concludes with good electrosurgery practice and techniques to increase safety and efficacy of target vaporization.

Basic physics of catheter electrosurgery

This section is intended to give the interventional physician a working understanding of the principals of charge concentration to heat and vaporize target tissue using transcatheter tools. An understanding of these mechanisms will help enable the operator to use these techniques safely and effectively.

Tissue heating and dielectric properties

The goal of transcatheter electrosurgery is to cut tissue, whether to modify structures or allow device traversal.

Electrosurgery relies on tissue conducting alternating current between 2 electrodes. High frequency alternating currents (~500KHz, or ‘radiofrequency’) do not stimulate nerve and muscle tissue and thus avoid pain, muscle contraction, and myocardial fibrillation (2).

Current conducting through tissue causes resistive heating. Heat is generated by collision of ions and corresponds to the work done by charge carriers (ions or electrons) to travel to a lower potential. At a certain threshold, the delivered energy breaks down polar molecules (for example, water) to create mobile charge particles (for example, protons and hydroxide ions). This process, called dielectric breakdown, causes an exponential rise in tissue heating.

Table 1 shows the behavior of tissues heated to different temperature thresholds at sea level (1,3). The conductivity of tissue increases with its water content. Tissues with high water content include muscle, skin, kidney and liver. Tissues with intermediate water content include brain, lung and bone marrow. Tissues with low water content include fat and bone(1). Tissue permittivity and conductivity values are shown in TABLE 2. These values explain why calcified tissues are harder to vaporize using radiofrequency energy, as are synthetic non-conductive materials like certain sutures and graft materials.

Table 1.

Known tissue effects of heating(1,3)

Temperature	Tissue effect
49° C	Tissue coagulates
60° C	Protein denatures
70° C	Cells desiccate
100° C	Cells rupture from vaporization of intracellular water

Table 2. Known tissue dialectric properties.

The tissue dielectric parameters are computed according to the 4-Cole-Cole Model (68) at frequency = 10.00 MHz.

Tissue	Electrical Permittivity (ε)	Electrical Conductivity (σ)
Blood	280	1.10
Bone Cancellous	71	0.12
Bone Cortical	37	0.04
Fat	14	0.03
Heart	293	0.50
Lung (Inflated)	124	0.23
Muscle (Parallel Fiber)	149	0.67
Muscle (Transverse Fiber)	171	0.62
Skin (Wet)	221	0.37

Radiofrequency waveforms: cutting versus coagulation

Targeted tissue vaporization requires a rapid and focal increase in current density, and hence temperature rise. This is achieved using continuous alternating currents at high voltages over short treatment times (4). Interrupted waveforms, including all varieties of ‘blended’ waveforms, allow intercurrent cooling resulting in slower heating and are intended to cause coagulation (1) [Figure 1]. While coagulation may be desirable in surgical applications to stop bleeding, in the transcatheter endovascular setting blood coagulation may cause stroke and other thromboembolic events. Moreover, at slower temperature rises, tissues desiccate over wide distances, with loss of water content and reduced conductivity, making the tissue more difficult to vaporize. These properties are exploited in radiofrequency ablation for treating arrythmias(5). Steam pops, the audible sounds produced by intramyocardial tissue vaporization, are a complication of electrophysiological ablation and are avoided by controlling the temperature rise. Conversely, tissue vaporization is the goal of transcatheter electrosurgery.

Figure 1: Cutting versus coagulation radiofrequency waveforms.

Schematic diagram of typical radiofrequency (RF) waveforms in cutting mode, intended to vaporize tissue, compared with coagulation mode, intended to stop bleeding. Cutting mode is typically activated using a yellow-colored button on electrosurgical pencils, and is associated with continuous-duty radiofrequency energy that constantly heats tissue until it vaporizes. Coagulation mode, activated typically using blue-colored buttons on electrosurgical pencils, applies interrupted-duty waveforms. The interrupted waveforms cause rapid heating-cooling cycles that allow blood to coagulate.

Plasma Arcs

Plasma arcs form when the medium between 2 electrodes ionizes due to a strong electric field. If ionized molecules bump into other molecules with sufficient energy, they ionize too, leading to avalanche multiplication, creating a plasma cloud. The impedance of the medium drops and current increases. Small area arcs concentrate current onto the tissue, which is why cutting with the electrosurgical knife in the plasma cloud at a distance is more effective than when it touches tissue. At sufficient power, dramatic plasma arcs are created and contribute to tissue vaporization [Video 1]. Some electrosurgery generators attempt to reduce power in response to sudden impedance drops, in order to suppress arcing.

Current density

The rate of heating depends on current density in the tissue. We performed simulations to demonstrate the key principals of charge concentration required for transcatheter electrosurgery, and to inform transcatheter electrosurgical techniques.

Current density simulation

Methods

The current density simulations were performed using the AC/DC module on Comsol Multiphysics (Comsol Inc. MA,USA) simulation software. The biological structures were represented as simplified geometries in the simulation setup to reduce the computational cost. A 60cm height and 25cm diameter cylinder was used as the blood pool. A 3mm height and 10cm diameter disk was placed at the bottom of the blood pool to be used as the ground path. The leaflet and the myocardial tissues were represented with a 2cm × 0.5cm × 5cm and a 3cm ×20cm × 20cm rectangular blocks, respectively. A 0.014” guidewire with 0.001” PTFE insulation (representing an Astato XS 20 guidewire, Asahi Intecc, Japan) was used as the energized wire. A 3Fr microcatheter was used over the energized wire. A 100W power source was used with 100V and 1A voltage and current outputs at 700kHz to simulate commercially available electrosurgery units. The conductivity and the relative permittivity values were used as 79 and 63 mS/cm for the blood, 61 and 49mS/cm for the leaflet and the myocardial tissues, respectively (6). The conductivity and the relative permittivity values of dextrose were extrapolated for 700kHz and set as 72 and 0.5mS/cm, respectively (7). The dielectric constant of PTFE coating was set as 2.1 (8).

Simulations were run for a comprehensive set of conditions to assess the effects of guidewire denudation length, the use of insulating microcatheters and the use of dextrose on the current density in blood and the myocardial tissue. First, the effect of the guidewire insulation length was studied for a unipolar electrode in blood and in contact with the myocardial tissue in blood. Then a pair of bipolar electrodes were simulated to compare the current density around and in between the guidewire electrodes between the unipolar and bipolar setups. Finally, leaflet laceration conditions were simulated on a kinked wire straddling the leaflet tissue. Kinked wire variations included intact insulation, insulation focally denuded from the inner-surface of the kink, the impact of adjacent insulating microcatheters, and the impact of flooding the field with dextrose to displace conductive ions in solution. The current density values were plotted for each condition in arbitrary units.

Impact of different electrosurgical guidewire configurations

Extending an un-insulated electrosurgical guidewire beyond the tip of a catheter allows current to disperse and thereby reduces its ability to vaporize and traverse tissue. Figure 2 demonstrates that current density decreases exponentially as the guidewire electrode is extended beyond the insulating catheter tip. Current density also decreases exponentially with increased distance from the guidewire electrode. Therefore, both limiting the area of exposed guidewire electrode and close approximation with the target tissue are important for generating sufficient current density to vaporize tissue.

Figure 2: Insulating a guidewire shaft (with a catheter) concentrates charge at the tip and improves effectiveness.

Simulation depicting the electric field around a conductive guidewire as it progressively extends beyond an insulating catheter. The top row shows long-axis views and the bottom row shows the cross-sectional views of the field in arbitrary units. On the left, a guidewire is extending far beyond the tip of an insulating catheter, resulting in a modest electrical field around the guidewire tip. Moving towards the middle and right columns, the guidewire is extended only minimally beyond the tip of the insulating catheter, resulting in marked enhancement of the electrical field. This focused insulation significantly increases electrosurgical efficiency, for example, during tissue traversal.

Exposing an electrosurgical guidewire to blood also reduces cutting efficiency. Figure 3 depicts a catheter delivering an electrified guidewire into tissue though blood, compared with the same catheter abutting tissue to deliver the electrified guidewire. As always, current follows the path of least resistance. The wire spans a medium with higher conductivity (blood) and a medium with lower conductivity (aortic valve leaflet), resulting in preferential current flow into the high conductivity medium (blood). In this case, there will be no current concentration, and therefore little resistive heating and ‘cutting’ of the target tissue, such as aortic valve leaflet in BASILICA. However, if the guidewire is insulated using a microcatheter, current will concentrate in and vaporize the target tissue.

Figure 3: Electrosurgical guidewires should contact tissue directly; blood contact reduces effectiveness.

Simulation depicting a guidewire spanning blood and tissue. In the left column the guidewire is exposed in both blood and tissue, with most of the current following the path of least resistance and dispersing in blood. In the right column the guidewire is insulated from blood so current concentrates through tissue. The bottom rows show cross-sectional views at the level of blood and of tissue, respectively.

All electrosurgery involves current flow between 2 electrodes. Figure 4 demonstrates current densities in unipolar and bipolar modes. In unipolar mode, current flows between an “active electrode” at the target tissue and a broad “indifferent” or “dispersive electrode” at a remote site on the skin surface. In a bipolar setup, 2 active electrodes are in close proximity to each other. Bipolar modes generate a larger electric field and have traditionally been used for coagulation rather than vaporization, using lower energy between 2 closely positioned static electrodes (1,9). Using static active electrodes is undesirable in transcatheter electrosurgery because of electrode carbonization and collateral tissue heating and coagulation. Traditionally, unipolar modes have been used for tissue cutting, generating concentrated current at an active electrode tip as it moves through the target tissue. Precisely applied, unipolar radiofrequency can vaporize cells adjacent to the guidewire electrode and spare cells only a few layers deep as current decreases exponentially with the radial distance from the source (1,10). To date, few transcatheter electrosurgery applications employ bipolar mode.

Figure 4: Unipolar versus Bipolar modes.

Simulation comparing current density achieved with an exposed unipolar guidewire tip with 2 exposed bipolar guidewire tips, one black and one white, at progressively larger separation distances. Note the electrical field lines. Bipolar electrosurgery is less effective at-a-distance. The scale shows relative current density.

The above demonstrations describe electrosurgical traversal of tissue or valve leaflets using the tip of a guidewire. To slice or lacerate a valve leaflet is more challenging. The simplest approach to electrosurgical leaflet laceration is to cross the leaflet to straddle both sides and then apply traction during electrification. Traction causes the guidewire to bend at the “lacerating surface” where it contacts the leaflet edge being cut. The lacerating surface is more effective if specially configured. Figure 5 simulates current density using the kinked mid-shaft of a guidewire, which serves as the lacerating surface. Using an unmodified guidewire having intact PTFE coating, there is insufficient charge conducted from guidewire to tissue. After focally denuding the inner surface at the guidewire kink, charge density around the lacerating surface increases but there is still charge dispersal along the guidewire shaft. With insulating microcatheters positioned on either side, charge dispersal along the guidewire shaft is reduced, but most of the charge still disperses in blood adjacent to the tissue. After displacing blood with 5% dextrose, a non-ionic fluid, alternative current paths are minimized and charge concentrates in tissue without heating the surrounding blood pool. This allows focal vaporization of target tissue at lower power outputs and minimizes char, coagulation, and possible thromboembolism in blood. Concentrating current on target tissue by displacing ionic solution with a non-ionic solution is not unique to transcatheter electrosurgery. For example, during transurethral electrosurgical resection of the prostate, the urethra is irrigated with sterile non-conductive solution (dextrose or glycerin) (11).

Figure 5: Charge density at the “Flying V” is highest when combining inner-surface denudation, insulating catheters, and dextrose flush.

Impact of focally denuding a kinked guidewire used for electrosurgical laceration of leaflet tissue, depicted on electromagnetic simulations. (A) Schematic diagram of an electrified Flying V in position across a leaflet to be lacerated. (B) Charge is dispersed, and even slightly higher, around the outer curve of a kinked guidewire straddling a leaflet. (C) Focally denuding the inner-surface of the kinked wire increases charge on the inner lacerating surface. (D) Apposing 2 insulating microcatheters further enhances charge concentration on the inner lacerating surface. (E) Flooding the field with non-conductive dextrose displaces blood ions and further concentrates charge, contributing to more effective electrosurgical laceration.

In vitro laceration testing

We tested the optimal configurations for the guidewire together with a variety of insulation strategies. A benchtop model with freshly explanted pig aortas in a saline bath was used to test different insulating conditions for electrosurgical laceration (Figure 6A&B). The pulling force was maintained at 5N and 30W of “pure cut” radiofrequency energy was delivered for 2s, and tested in triplicate. These parameters were chosen as they produced replicable cutting results in vitro. The laceration distance was measured and compared.

Figure 6: Optimizing charge density at the “Flying V”.

Benchtop setup and results of testing different guidewire charge concentration strategies in pig hearts. (A) the pig hearts are submerged in saline and the traversal wire is positioned in a typical transcatheter electrosurgery configuration with suitable guiding catheters and microcatheters attached to a force meter (B). Panel (C) shows progressive electrosurgery strategies compared using the distance lacerated in a given time. More effective strategies traverse a greater distance, including inner-surface denudation, closely-apposed microcatheters, and flooding the ionic fluid field with non-ionic dextrose.

The results showed no significant cut when an unmodified guidewire was used, or when the midshaft was circumferentially denuded. With a partially denuded guidewire that was kinked to enforce the denuded segment onto the target tissue, a steady laceration was achieved. Additional insulation strategies with microcatheters (Piggyback, Teleflex, NC) and 5% dextrose flush demonstrated incremental benefit (Figure 6C).

This experiment emphasizes the importance of inner curvature charge concentration via selective denudation, and of robust insulation with both micro-catheters and non-ionic fluid, to concentrate charge for tissue laceration. These essential concepts underlie the clinical techniques employed below for mitral and aortic leaflet laceration.

Commercially available equipment for catheter electrosurgery

Electrosurgery Generators

There are a variety of electrosurgical generators available. The experiments below were all performed with the Valleylab ForceFx generator (Medtronic, MN). Different power settings may be required with other commercial generators, many of which have adaptive circuitry to modulate power output in response to dynamic impedance changes. Baylis Medical (Baylis Medical USA, MA) markets purpose-built guidewires, needles and generators for transcatheter electrosurgical traversal.

Comparative electrosurgical properties of commercial guidewires

Although electrosurgical equipment is commercially available from at least one vendor (Baylis), we usually use other commercial off-the-shelf guidewires for transcatheter electrosurgery, off-label, because they provide mechanical features not available in approved products. We tested guidewires from different major manufacturers to determine suitability for catheter electrosurgery. Guidewires were categorized by core material (stainless steel versus nitinol), tip style (core-to-tip versus fused shaping ribbon), tip cover (bare spring coils versus spring coils covered in a polymer jacket), and hydrophilic tip coating to determine different totalguidewire conduction properties.

Freshly explanted pig hearts were incompletely submerged in a saline bath. Guidewire tips were apposed to myocardial tissue and secured 5cm proximally. Guidewire distal shafts were manually denuded of insulating polymer coating and then clamped to an electrosurgery generator (Valleylab Force Fx). The guidewire shaft was suspended in air, resembling perfect insulation with only the tip in contact with saline and myocardial tissue. The minimal power required for instantaneous vaporization, judged by unimpeded rapid wire traversal, was noted [TABLE 3].

Table 3: Observed power (Watts) required for commercial guidewires to traverse tissue under the described in vitro conditions.

Guidewires (0.014”) that require low traversal power and that have high tip loads appear best suited for transcatheter electrosurgery (highlighted in green). Guidewire models that failed to traverse even at the highest tested energy (30W) are indicated with an asterisk (*). These non-traversing models were tested again after manually stripping distal polymer insulation (highlighted in orange), at which point they successfully traversed the target tissue at acceptable power.

Required Power (W)	Exposed (uninsulated) distal spring coil	Sample ID	Manufacturer	Length	Distal tip coating	Tip load
Chronic total occlusion guidewires
7	Yes	Confianza Pro-9	Asahi	300	hydrophilic except distal 1mm	9
7	Yes	Approach CTO-6	Cook	300	hydrophilic	6
8	Yes	Astato XS 20	Asahi	300	hydrophilic except ball tip	20
8	Yes	MIRACLEbros 6	Asahi	180	hydrophobic	6
8	Yes	ProVia 9	Medtronic	300	hydrophilic	9
8	Yes	Progress 200T	Abbott	190	hydrophobic	13
9	Yes	Samurai	Boston	190	hydrophilic	1.2
>30*	No	Pilot150	Abbott	190	hydrophilic	2.7
>30*	No	Shinobi Plus	Cordis	300	hydrophilic	4
Extra support guidewires
8	Yes	Iron Man	Abbott	190	hydrophobic	1
8	Yes	Grand Slam	Asahi	180	hydrophobic	0.7
8	Yes	Platinum Plus	Boston	180	hydrophilic	7
12	Yes	Mailman	Boston	182	hydrophilic except distal 3cm	0.8
Workhorse guidewires
9	Yes	Runthrough NS extra floppy	Terumo	180	hydrophilic
11	Yes	Balance Middle Weight	Abbott		hydrophilic	0.7
11	Yes	Kinetix	Boston	185	hydrophilic except distal 1.27cm	0.8
13	Yes	Choice Floppy	Boston	182	hydrophobic	0.8
>30*	No	Fielder	Asahi	180	hydrophilic	1
>30*	No	Whisper	Abbott	300	hydrophilic	1
Distal polymer manually stripped to expose conductive spring coils
7	Yes	Fielder
8	Yes	Whisper
8	Yes	Pilot 150
8	Yes	Shinobi Plus

The results showed that guidewire polymer coating acts as electrical insulation. Guidewires with a polymer jacket coating the tip did not penetrate tissue even at 30W, whereas guidewires with uncoated bare spring coils penetrated tissue without hindrance at 7–13W. When the polymer jacket was excised with a scalpel to expose the spring coils, the guidewires performed similarly to uncoated guidewires. Design parameters such as core material (steel versus nitinol), design (core-to-tip versus fused), and presence of shaping ribbon did not appear to influence electrosurgical performance because all tested metal systems appeared highly conductive. Guidewires with a high tip load appear more suitable for transcatheter electrosurgery as they are less likely to prolapse when attempting traversal.

Empirical experience suggests that a guidewire tip voltage of 70V or greater is required for tissue traversal (12). Voltages at the guidewire tip in a saline bath were measured by oscilloscope at a fixed power output. As expected, the voltage decreased exponentially with increased wire exposure in saline. To test properties of different guidewires, all guidewires were tested with 2mm of the tip exposed through an insulating polymer jacket (Piggyback Wire Converter, Teleflex, NC). Guidewires achieved 70V tip voltage when 5–13W power was applied, which corresponds with the traversal tests.

Clinical applications

There are three broad applications for transcatheter electrosurgery: radiofrequency perforation to recanalize occlusive lesions; radiofrequency perforation to traverse tissue between 2 cardiovascular chambers; and radiofrequency laceration to make linear cuts in tissue (Central Illustration).

Central Illustration: Clinical applications of transcatheter electrosurgery.

Transseptal puncture: fluoroscopy demonstrating an electrified Astato 0.014” guidewire within a deflectable sheath traversing the inter-atrial septum. Transcaval access: fluoroscopy demonstrating guidewire traversal from vena cava into a snare in the abdominal aorta. On completion of TAVR, the tract is closed with a nitinol occluder and final angiography demonstrates a satisfactory (type 1) closure with persistent aortocaval fistula. Cavo-pulmonary shunt: Fluoroscopy demonstrates electrified guidewire traversal from superior vena cava to pulmonary artery, followed by implantation of a covered stent to accomplish a bidirectional Glenn shunt. BASILICA: Illustration showing laceration of the left bioprosthetic aortic valve leaflet prior to TAVR to prevent coronary artery obstruction. Volume-rendered CT after BASILICA TAVR in a patient demonstrates spit left (red) and right (green) leaflets parting around the ostia of the left and right coronary arteries. LAMPOON: Illustration demonstrating laceration of the anterior mitral valve leaflet from base to tip along the centerline. Volume-rendered CT after LAMPOON TMVR in a patient demonstrates split anterior mitral valve leaflet with preserved chordae parting around a Sapien 3 valve, preventing LVOT obstruction. ELASta-Clip: Fluoroscopy images showing transcatheter electrosurgical release of a mitral anterior leaflet bearing 2 Mitra-Clips. First, a pair of deflectable sheaths across the interatrial septum guide the “Flying V” (black arrow) to the anterior mitral leaflet attachment of 2 MitraClips (white arrows). Following laceration, TMVR with a Tendyne valve is performed, and the Mitra-Clips are displaced and retained posteriorly (white arrows).

Radiofrequency perforation to recanalize occlusive lesions

Pulmonary atresia

The first transcatheter use of radiofrequency energy was to perforate atretic pulmonary valves in patients with congenital heart disease and intact ventricular septum (13). Purpose built wires were connected to a radiofrequency generator and directed by catheters positioned below the atretic valve. The wire was electrified and advanced through the valve into the pulmonary artery and balloon dilatation performed.

Several groups have since published their experience with radiofrequency perforation and balloon dilation in pulmonary atresia demonstrating both immediate success and satisfactory long-term outcomes with and without downstream surgery (14–18). It is now an acceptable first line treatment for this uncommon application (19).

Vascular occlusion

Radiofrequency perforation using both off-the-shelf and dedicated devices (PowerWire RF, Baylis Medical Company) have been used to recanalize peripheral and central vascular occlusions following failed conventional antegrade and retrograde attempts. These include subclavian vein occlusion (4,20), non-malignant superior vena cava obstruction(21), anterior and posterior tibial arteries, common iliac vein, and superior vena cava (18), acquired chronic total occlusion of the left pulmonary artery (22), acquired right pulmonary artery atresia (23), interrupted aortic coarctation (24), and re-entry for ostial right coronary artery chronic total occlusion (25). The Safe Cross radiofrequency guidewire (DSM, Heerleen, Netherlands) combined optical coherence reflectometry and radiofrequency energy to tackle chronic totally occluded coronary lesions(26) and the PlasmaWire (RetroVascular, Asahi Intecc, Japan) uses bipolar radiofrequency guidewires either side of chronic totally occluded arteries(27). The former is no longer marketed, and the latter is not yet marketed.

Transcatheter electrosurgery has been used to successfully restore flow following iatrogenic occlusion of the right pulmonary artery, by bioprosthetic bovine jugular vein material, after transcatheter pulmonary valve replacement with a Melody valve (Medtronic, Minneapolis, MN) (28).

Radiofrequency perforation of tissue planes between cardiovascular chambers

Atrial septal puncture

Atrial septal perforation using radiofrequency energy has been performed through a coaxial injectable catheter and radiofrequency wire (Nykanen Radiofrequency Perforation Catheter, Baylis Medical Company) (29). A randomized control trial comparing radiofrequency and needle transseptal access found reduced procedure time, reduced procedure failure, and reduced plastic particulate matter with the radiofrequency system (NRG Transseptal needle, Baylis) (30).

Atrial septal radiofrequency assisted perforation has been performed in newborns with hypoplastic left heart syndrome (31). Atrial septal puncture has also been achieved by electrifying a Brockenbrough needle (32–34), or a coronary guidewire advanced through a transseptal dilator and sheath (35).

Ventricular septal puncture

The ventricular septum has been perforated using radiofrequency energy to create a ventricular septal defect in a patient with double outflow right ventricle and restrictive ventricular septal defect (36). Radiofrequency perforation was used to access the left ventricular endocardium for a ventricular tachycardia ablation in a patient with mechanical aortic and mitral valves (37). It has also been used to position an endocardial left ventricular lead for cardiac resynchronization therapy (38,39).

Radiofrequency and valve repair

Pledget-assisted suture tricuspid annuloplasty (PASTA) uses off-the-shelf guidewires to traverse myocardial and annular tissue, and then exchange these guidewires for suture to effect transcatheter tricuspid annuloplasty resulting in a double orifice valve(40). The annulus is traversed with electrified guidewires at target sites on the septal and anterior wall. The guidewires are exchanged for sutures that then plicate the annulus to create a double orifice valve. PASTA is especially interesting because suture exchange for electrified guidewires is an early step towards transcatheter surgery with suture delivery.

The Mitralign system (Mitralign Inc, Tewksbury, MA), which is not commercially available, uses an insulated radiofrequency crossing wire through the mitral or tricuspid annulus at adjacent positions to eventually cinch the annulus to reduce regurgitation (41).

Intervascular traversal and extra-anatomic bypass

Transcaval access

Transcaval access is an alternative large bore access route when femoral artery access is not suitable for TAVR or mechanical assist devices. A stiff coronary guidewire (Astato XS 20 or amputated Confianza, Asahi Intecc) is insulated in a polymer jacket (Piggyback, Teleflex, NC) or other microcatheter and connected to an electrosurgery pencil and generator. The wire is electrified at 50W briefly during advancement out of the vena cava into the abdominal aorta, where it is snared and exchanged for a stiff wire over which the large bore sheath is advanced. TAVR is performed as if it were via usual transfemoral access. Arterial extravasation, if any, spontaneously decompresses via the hole in the adjoining vena cava. On exit, the hole in the aorta is closed with a nitinol cardiac occluder at the end of the case (42,43) or with a dedicated occluder device (Transcaval Closure Device, Transmural Systems, Boston) (44). In the prospective 100 patient NHLBI Transcaval TAVR trial, transcaval access was successful in 99% (45). There were no late vascular complications out to 1 year(46). The experience was independently validated in Europe (47). Transcaval access has also been used to percutaneously deliver large bore mechanical circulatory assist devices (5.0 Impella, Abiomed, Danvers, MA), averting surgical implantation (48).

Reverse Potts shunt

Transcatheter electrosurgery enables a non-surgical reverse Potts shunt to decompress severe (supra-systemic) pulmonary artery hypertension. A radiofrequency wire is advanced from the aorta into the left pulmonary artery, exchanged for a stiff wire and a covered stent allows a right-to-left shunt that bypasses the cerebral circulation (49).

Glenn shunt

Radiofrequency energy was used for guidewire traversal between superior vena cava and pulmonary artery to create a catheter-only, closed chest, large vessel anastomoses, equivalent to a bidirectional superior cavopulmonary anastomosis (Glenn shunt) (50–52). A purpose-built transcatheter Glenn shunt device is under development.

RF through synthetic material

Transcaval TAVR has been performed through a polyester aortic graft(53) and radiofrequency assisted transseptal puncture through an atrial septal patch repair(35). TEVAR fenestrations have been performed through polyester grafts (Valiant, Medtronic Vascular, Santa Rosa, CA; Zenith TX2, Cook Medical, Bloomington, IN) (54).

Radiofrequency laceration and the “Flying V”

Applications described above all require pinhole perforation with the tip of an insulated guidewire. For tissue laceration, controlled targeted directional radiofrequency delivery is required, with greater care to avoid charring and coagulation during longer and higher energy applications.

The mid-shaft of a 300cm 0.014” steel guidewire is selectively denuded of PTFE insulation in a 90-degree circumferential arc and along 4–5mm of the guidewire length. This section is then kinked so that the denuded portion of guidewire is confined to the inner curvature of the kink. The guidewire forms the “Flying V” shape of the iconic rock guitar [Figure 6]. The lacerating edge is positioned at the tissue intended for laceration and the 2 limbs of the guidewire are sheathed in catheters. It is recommended to displace blood from the field using a non-ionic liquid flush, typically 5% dextrose. This promotes charge concentration in the target tissue, and prevents blood coagulation. Transcatheter electrosurgical laceration has been applied to prevent a number of complications in the setting of transcatheter valve replacement.

LAMPOON

Intentional Laceration of the Anterior Mitral leaflet to Prevent Outflow ObstructioN (LAMPOON) uses inner-curvature charge concentration to cut the anterior mitral leaflet to prevent left ventricular outflow tract (LVOT) obstruction during transcatheter mitral valve replacement (TMVR) (55,56). The base of the A2 scallop of the anterior mitral valve leaflet is traversed from the LVOT with an Astato guidewire sheathed in a Piggyback microcatheter using <1s of continuous duty “pure cut” radiofrequency energy at 30 Watts. The guidewire tip is snared in the left atrium. The mid-shaft of the guidewire (still outside the body) is denuded and kinked to form the Flying V, which is then advanced to straddle the anterior mitral valve leaflet. Guiding catheters are positioned along each limb of the guidewire so only the kinked portion is exposed. The catheters are flushed with 5% dextrose to displace blood and insulate the length of the guidewire. Continuous duty “pure cut” radiofrequency energy at 70 W is applied for 1–5s while the guidewire and catheters are pulled to create a controlled midline laceration of the anterior mitral valve leaflet. The chordae are preserved during LAMPOON. TMVR is performed and the anterior leaflet splays away from the LVOT, allowing blood to flow through the open cells of the valve frame and preventing systolic anterior motion (SAM) of the valve tip, preventing LVOT obstruction. Serendipitously, lacerated leaflets typically appose sufficiently that most patients tolerate the interval between laceration and TMVR without hypotension

The prospective NHLBI LAMPOON trial demonstrated LAMPOON success in all subjects undergoing TMVR in MAC or ring with prohibitive risk of LVOT obstruction, with 97% exiting the catheter laboratory without LVOT obstruction despite the high predicted risk(57). There were no strokes and 30 day survival was 93%, significantly better when compared to patients who were not protected and developed LVOT obstruction (38%)(58). A simplified “antegrade” transseptal technique has recently been adopted (59).

“Rescue” or “tip-to-base” LAMPOON can be used after TMVR to treat LVOT obstruction by lacerating the protruding tip of the anterior mitral valve leaflet and treating SAM(60). The use of LAMPOON with dedicated TMVR devices remains to be tested. It has enabled Tendyne TMVR when there was high risk of LVOT obstruction(61). However, it cannot prevent obstruction if the fabric skirt of the valve obstructs the LVOT(62).

BASILICA

Bioprosthetic or native Aortic Scallop Intentional Laceration to prevent Iatrogenic Coronary Artery obstruction (BASILICA) utilizes inner curvature charge concentration to lacerate the aortic valve leaflets to prevent coronary artery obstruction during TAVR(63,64). In patients at risk of coronary artery obstruction, the target aortic leaflet or leaflets are traversed with an Astato guidewire sheathed in a Piggyback microcatheter at 30W continuous duty “pure cut” radiofrequency energy for <1s. The Flying V is formed at the guidewire mid-shaft and positioned to straddle the valve leaflet. Guiding catheters sheath both limbs of the guidewire leaving only the Flying V exposed. The guidewire and catheters are pulled during 1–2s of radiofrequency application at 70W and continuous 5% dextrose infusion. The split leaflet splays away from the coronary artery after TAVR and also prevents sealing the sinus off at the level of the sino-tubular junction. Just as in LAMPOON, lacerated leaflets typically appose sufficiently that most patients tolerate the interval between laceration and TAVR without hemodynamic compromise.

The NHLBI BASILICA trial demonstrated successful BASILICA and successful TAVR without coronary obstruction or re-intervention in 93% of subjects at high risk of coronary obstruction with TAVR(65). There was one disabling stroke (3%) and 30 day survival was 97%. ELASTIC and ELASta-Clip

Electrosurgical Laceration of Alfieri STItCh (ELASTIC) and Electrosurgical Laceration and STAbilization of a mitral Clip (ELASta-Clip) uses this technique to liberate the anterior mitral leaflet from a surgical coaptation stitch or transcatheter clip device to create a single orifice prior to TMVR(66). The clip or stitch may be accessed antegrade via a transseptal approach or retrograde from the femoral arteries. Catheters are positioned in each mitral valve orifice and guidewire is passed from one and snared from the other. The Flying V is positioned along the anterior mitral valve leaflet edge of the clip or stitch, which is lacerated during 1–5s of radiofrequency energy application at 70W with a continuous dextrose infusion. The clip or stitch remains on the posterior mitral valve leaflet and TMVR is performed, pinning the liberated device to the posterior ventricular wall (67).

Risks and Limitations

Thromboembolism due to char, coagulum, or tissue debris released by laceration could cause stroke or myocardial infarction. Cerebral embolic protection may be considered in selected cases. Prolonged or excessive current delivery could cause injury to adjacent structures. Collateral tissue damage is also increased with greater guidewire exposure. At higher power outputs, excessive charge may concentrate at the guidewire tip leading to extreme temperature rises that can result in melting of the solder binding the guidewire spring coils to the inner steel core. Insufficient charge density during laceration, combined with excessive mechanical force, can result in a mechanical leaflet tear which can cause avulsion of the target valve leaflet leading to ineffective split and splay, severe valve incompetency and hemodynamic compromise. Similarly, buckling of a transcaval traversal guidewire during electrification can cause a long linear laceration rather than a pinhole traversal.

Many of the techniques described require careful patient selection and planning. Some of the more advanced procedures are best performed in the hands of experienced operators at high volume centers or with the help of experienced proctors.

Optimizing transcatheter electrosurgery

Rapid perforation, caused by higher voltages, smaller electrode diameters and lengths, and continuous duty cycle radiofrequency current in unipolar mode reduces collateral tissue damage. The shorter duration of energy delivery prevents tissue desiccation and coagulum formation(12). The electrosurgery generator should be set to pure cut and at the lowest power output that achieves instantaneous tissue vaporization with minimal radial damage. Therapeutic anticoagulation is recommended prior to electrification to reduce thrombus formation.

The choice of guidewire may vary depending on application. For most uses, a guidewire designed for chronic total occlusion with high tip load and an uncoated hydrophobic tip is best. Guidewires with a polymer jacket at the tip are not suitable. Those with a low tip load are more likely to knuckle and create an uncontrolled slit rather than a small controlled perforation.

Purpose built electrosurgery guidewires are under clinical development.

If traversal is not achieved in clinical practice, we recommend the following troubleshooting steps. 1) Check all electrosurgical connections are secure, ensuring good grounding pad contact and secure connection between guidewire and electrosurgery generator. 2) Avoid electrical coupling between the guidewire and metallic implements or wet surfaces, and avoid tight loops in the guidewire. If echocardiography is available, it is useful to confirm the presence of microbubbles on electrification; 3) Ensure the guidewire is coaxial and stable against the target tissue; palpation with the guidewire is essential and tactile feedback should indicate apposition to the tissue without skidding; 4) Ensure the guidewire is appropriately insulated with a snug microcatheter with only 1mm of the guidewire tip exposed; 5) Alter position slightly to find a calcium-free target if the tissue is heavily calcified; 6) Increase the power output on the electrosurgery generator.

Successful electrosurgical laceration requires correct formation of the “Flying V”, careful insulation with catheters and a 5% dextrose flush, and higher energy settings than required for traversal (typically 70W). Common pitfalls with laceration include inadvertent prolapse of the microcatheter through the target leaflet, and sliding catheters from pulling exposing too much wire resulting in insufficient charge density. Locking the relationship between catheters, microcatheters, and guidewire with torque devices and rotational hemostatic catheter hubs mitigates these problems.

Future Perspectives

Clinical evidence for transcatheter electrosurgery remains scarce, with few prospective studies and almost no large registries or randomized trials. The STS/ACC TVT Registry started collecting data on transcaval access, BASILICA and LAMPOON in 2019. These registries will provide valuable real-world data beyond what was reported in the early feasibility trials.

Dedicated devices for transcatheter electrosurgery, particularly a lacerating guidewire, will make the procedures easier and more reproducible. Dedicated devices may also enable the expansion of the this technique to tissue excision, which may be useful for leaflet removal, or myocardial or tumor debulking.

Conclusion

If done well, transcatheter electrosurgery can be used to vaporize target tissue safely and effectively without collateral damage. The ability to cut tissues endovascularly takes interventional cardiologists one step closer to true transcatheter surgery.

Supplementary Material

Videos

Video 1 Plasma arcs. Astato guidewire with 4mm exposed in egg white solution through a Piggyback microcatheter with 30W of energy. Current concentrates at the tip of the insulated guidewire demonstrating a plasma arc. The bright colored light is created by the ion cloud.

Video 2 BASILICA recorded case. A recorded case of a BASILICA procedure showing bioprosthetic valve leaflet traversal and laceration followed by TAVR in a patient at high risk of left coronary artery obstruction.

Table 4:

Representative clinical applications of transcatheter electrosurgery

Application	References	Study type	Total patients	Procedure success	Complications
Pulmonary valve atresia traversal in newborns	Veldtman 2004 (18)	Case series	136	87% successful in establishing antegrade flow	Procedural death (7%); Arrhythmia, RVOT perforation (16%)
Central chronic total venous occlusion traversal (subclavian vein, SVC)	Baerlocher 2006; Iafrati 2012; Foerst 2017 (4,20,21)	Case reports	6	100%	None reported
Coronary chronic total occlusion	Baim 2004 (26)	Prospective multicenter registry	116	54%	Perforation and tamponade (2.6%)
Transseptal puncture	Hsu 2013 (30)	Randomized control trial	36 RF; 36 conventional	100% RF; 72% conventional (with crossover to RF and subsequent success)	Pericardial effusion (2.8%)
Interventricular septum puncture (for LV lead placement)	Gamble 2018 (39)	Prospective single center single arm clinical trial	20	100% success in ventricular traversal	Disabling stroke (5%)
Transcaval for large bore access for TAVR	Greenbaum 2017(45) Lederman 2019(46) Costa 2019(47)	Prospective multicenter single arm clinical trial Retrospective registry	150	99%	Life-threatening or disabling bleeding (4-12%) Note late complications
LAMPOON to lacerate the anterior mitral valve leaflet prior to TMVR	Khan 2019 (57)	Prospective multicenter single arm clinical trial	30	100%	More than mild paravalvular leak (23%); LVOT obstruction from valve skirt (10%).
BASILICA to lacerate aortic leaflets prior to TAVR	Khan 2019 (65)	Prospective multicenter single arm clinical trial	30	93%	Disabling stroke (3%)

Bullet Points.

• Transcatheter electrosurgery uses continuous duty-cycle radiofrequency energy to vaporize and therefore traverse or lacerate tissue.

• Tissue traversal requires guidewire insulation and adjunctive insulating catheters to concentrate charge at the tip of traversing guidewires.

• The Flying V configuration of a kinked guidewire can cut valve leaflets by concentrating charge at the inner lacerating surface of the guidewire and by eliminating alternative current paths using non-ionic dextrose flush.

• Applications include transcaval access, BASILICA, LAMPOON, ELASTa-clip and many others.

• Transcatheter electrosurgery is a logical step towards transcatheter surgery

Abbreviations

BASILICA

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

ePTFE

Expanded polytetrafluoroethylene

ELASTIC

Electrosurgical Laceration of Alfieri STItCh

ELASta-Clip

Electrosurgical Laceration And Stabilization of MitraClip

LAMPOON

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

LVOT

Left ventricular outflow tract

PASTA

Pledget assisted tricuspid annuloplasty

SAM

Systolic anterior motion of the mitral valve

TAVR

Transcatheter aortic valve replacement

TMVR

Transcatheter mitral valve replacement