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. The authors review theory, simulations, and benchtop demonstrations of how guidewires, insulation, adjunctive catheters, and dielectric medium interact. For tissue traversal, all but the tip of traversing guidewires is insulated 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). Tips are provided for optimizing these techniques. Transcatheter electrosurgery already enables a range of novel therapeutic procedures for structural heart disease, and represents a promising advance toward transcatheter surgery.

Keywords: BASILICA; ELASTA-Clip; LAMPOON; transcatheter electrosurgery; transcaval.

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.

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.

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.

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.

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.

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.

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).

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).