Radiofrequency ablation using a novel insulated-tip ablation catheter can create uniform lesions comparable in size to conventional irrigated ablation catheters while using a fraction of the energy and irrigation

Abstract

Introduction: During radiofrequency ablation (RFA) using conventional RFA catheters (RFC), ~90% of the energy dissipates into the bloodstream/surrounding tissue. We hypothesized that a novel insulated-tip ablation catheter (SMT) capable of blocking the radiofrequency path may focus most of the energy into the targeted tissue while utilizing reduced power and irrigation.

Methods: This study evaluated the outcomes of RFA using SMT versus an RFC in silico, ex vivo, and in vivo. Radiofrequency applications were delivered over porcine myocardium (ex vivo) and porcine thigh muscle preparations superfused with heparinized blood (in vivo). Altogether, 274 radiofrequency applications were delivered using SMT (4-15 W, 2 or 20 ml/min) and 74 applications using RFC (30 W, 30 ml/min).

Results: RFA using SMT proved capable of directing 66.8% of the radiofrequency energy into the targeted tissue. Accordingly, low power-low irrigation RFA using SMT (8-12 W, 2 ml/min) yielded lesion sizes comparable with RFC, whereas high power-high irrigation (15 W, 20 ml/min) RFA with SMT yielded lesions larger than RFC (p < .05). Although SMT was associated with greater impedance drops ex vivo and in vivo, ablation using RFC was associated with increased charring/steam pop/tissue cavitation (p < .05). Lastly, lesions created with SMT were more homogeneous than RFC (p < .001).

Conclusion: Low power-low irrigation (8-12 W, 2 ml/min) RFA using the novel SMT ablation catheter can create more uniform, but comparable-sized lesions as RFC with reduced charring/steam pop/tissue cavitation. High power-high irrigation (15 W, 20 ml/min) RFA with SMT yields lesions larger than RFC.

Keywords: SMT; catheter ablation; power; radiofrequency; steam pop.

Figure 1

The design of the SMT ablation catheter. SMT is a 9‐French, open‐irrigated ablation catheter, which consists of a central electrode measuring 2.3 mm × 4 mm, surrounded by four peripheral electrodes. The insulated‐tip design is intended to block the path of RF into the bloodstream and the surrounding tissue, to focus a greater magnitude of the delivered energy into the targeted tissue. The ablation catheter can be deployed and used in “vector” (A) or “linear” (B) configurations. In the vector configuration, the four deployable wings serve as a “landing gear,” intended to provide greater catheter stability and tissue contact during mapping and ablation.

Figure 2

Assessment of lesion homogeneity using RFC and SMT. RF lesion homogeneity was assessed by analyzing RGB images of ablation lesions and creating composite intensity graphs for RFC (A) and SMT (B) which were then represented by five best‐fit connected line segments. Subsequently, the width of the central maximally ablated segment was compared with the widths of the adjacent partially ablated segments to obtain a homogeneity score for RFC (C) and SMT (D). RGB, red−green−blue; RF, radiofrequency; RFC, radiofrequency ablation catheters

Figure 3

Computational modeling of RFC versus SMT. (A) Irrigation in SMT and RFC (ThermoCool) was modeled by fixing the electrode temperature (T _E) in a specific zone of the electrode. (B) Temperature distributions (scale in °C) and lesion boundaries for each catheter. (C) Spatial distributions of RF energy density (W/m³) applied around the electrode for each catheter. The values represent percentages of total RF energy dissipating into the blood, the targeted tissue, and the patient. As seen, a significantly greater proportion of the RF energy is directed into the targeted tissue with SMT (66.8%) versus RFC (13.7%). (D) Electrical current lines computed for each catheter. RF, radiofrequency; RFC, radiofrequency ablation catheters

Figure 4

RF lesion sizes created using RFC and SMT ex vivo. Lesion dimensions including surface diameter, maximum (max) diameter, depth, and volume using RFC (ThermoCool) at 30 W and SMT using varying power (6, 8, 10, and 12 W) for 30 s (A–D) and 60 s (E–H), respectively. RF, radiofrequency; RFC, radiofrequency ablation catheter

Figure 5

RF lesions created using RFC and SMT. Gross and cross‐sectional analysis of RF lesions created with RFC (ThermoCool) at 30 W, 30 ml/min, for 30 s (A, C) and SMT at 10 W, 2 ml/min, for 30 s (B, D), respectively. Close‐up images of lesions created using RFC (E) and SMT (F), respectively. Lesions generated with SMT were in general more uniform and homogeneous with narrower zones of transition. RF, radiofrequency; RFC, radiofrequency ablation catheters

Figure 6

RF lesion sizes created using RFC and SMT in vivo over porcine thigh muscle preparations. Lesion dimensions including surface diameter, maximum (max) diameter, depth, and volume using RFC (ThermoCool) at 30 W and SMT using varying power (6, 8, 10, and 12 W) for 30 s (A–D) and 60 s (E–H), respectively. RF, radiofrequency; RFC, radiofrequency ablation catheters

Figure 7

Charring and tissue cavitation during in vivo ablation using RFC. Charring (A) and a close‐up of the same (B) observed during ablation with RFC (30 W, 30 ml/min, for 30 s). Tissue cavitation in conjunction with a steam pop (C) and a close‐up of the same (D) that occurred during ablation using RFC (30 W, 30 ml/min, for 60 s). RFC, radiofrequency ablation catheters