Comparative assessment of the thermal footprints of pulse field ablation systems

Background

Pulse-field ablation (PFA) is a regarded as a non-thermal ablation modality, however there is an increasing number of reported complications that could be explained if there were significant thermal affects.

Purpose

Evaluate and compare clinical single-shot PFA systems’ thermal lesions using a validated thermal and electrical myocardial hydrogel phantom.

Methods

The hydrogel undergoes permanent colour change when a target temperature is reached allowing direct visualisation of the surface thermal footprint and depth. Hydrogel models calibrated to 50 oC and 60 oC were utilised.

Comparative lesion sets using a variable loop circular catheter (VP), circular over-the-wire catheter (PS) and pentaspline catheter (FP) were performed. Protocols included single and stacked applications and variation of force, irrigation, and voltage. The phantom hydrogel lesions were analysed en-face and by section, and lesion depth, total footprint area, and footprint length and width, were measured using digital image analysis.

Results

All catheters tested had significant thermal footprints. The VP catheter had the largest mean surface footprint (15.6mm2) and thermal depth (1. 31mm) compared to the other two catheters (PS 8.9mm2 & 1.24mm, FP 5.6mm2 & 1.05mm, p<0.005) (figure 1). Increasing irrigation showed a trend to reduce thermal footprint but did not reach statistical significance. Increasing voltage increased thermal footprint, but increasing force had negligible effect (figure 2). Stacked lesions incrementally increased thermal lesion footprint and depth in all catheters, though started to plateau after 3-4 lesions. Thermal depths of upto 2.4mm were observed when sectioned. Areas of darkening, degradation and dehydration of the hydrogel with possible char were observed with the VP and FP catheters, consisting of upto 47% of lesion area. No darkening was observed with the PS catheter.

Conclusions

This data uniquely assesses the thermal effects of PFA and allows visualisation of the thermal footprint. There are significant thermal footprints in all the systems tested and this is the first data to directly compare the thermal effects of 3 clinical systems. Temperatures exceeding 60oC have been demonstrated, comparable to radiofrequency ablation, and this may explain the mechanism of injury in reports of non-myocardial damage during PFA. The tissue selectivity of PFA will be reduced in the context of signficant thermal effects. The area of darkened samples for each catheter, possibly indicative of char, correlated with published stroke rates for the individual catheters. This may provide the mechanism of excess cerebrovascular injury reported with some PFA catheters. Caution should be exercised when describing PFA as a “non-thermal” ablation modality.Figure 1Figure 2