Does amount of contact matter for PEF ablation?
While research indicates a relationship between contact force and PEF treatment depth with focal catheters17, the LAF catheter investigated in this study did not demonstrate increased treatment depth with increased contact. LTC and HTC yielded similar lesion dimensions (approximately 6mm depth, 16mm width across all CTC ranges >∆10Ω). Unique catheter and electric field geometry contribute to this difference. Although LI is a measurement of electrode surface area in contact with resistive myocardium and not a direct measurement of contact force, LI has been shown to correlate with contact force over relevant operational ranges for focal catheters18. Similarly in this study, increased LI correlated with increased CTC; however, in contrast to a traditional solid-tip catheter, the LAF spheroid tip compresses in response to increased contact rather than indenting into the myocardium (Supplemental Figure 1 ). Additionally, solid-tip catheters produce small electric fields that are more susceptible to differences in contact than bigger LAF catheter electric fields 7. These mechanical behaviors and field-size discrepancies may explain the differing impacts of increased contact force on PEF treatment sizes for compressible LAF catheters versus solid-tip catheters. This study also indicates that the number of splines in contact and the amount of each spline in contact with myocardium do not influence lesion size if the spline(s) have stable CTC (Figure 7) .
With RF ablation, increased contact force leads to larger treatments, but also increased safety risks19. Increased CTC with the LAF catheter did not yield any additional safety risk. No damage to collateral structures, steam pops, perforations, or incidences of char were noted acutely or chronically for any CTC cohort. The spheroid catheter tip inherently lends itself to reduced risk of perforation and the flexibility of the nitinol splines allows force to be absorbed by the catheter rather than tissue, reducing tissue trauma. However, because the structure of the LAF catheter creates sizeable lesions even at LTC, splines that are in proximity to critical structures (e.g., AV node, HIS) should be closely monitored to prevent inadvertent damage. Tissue thinning and remodeling were noted after 30 days at ventricular lesion sites; observations similar to previous work with a different LAF catheter 20 and require further investigation (Supplemental Figure 2 ).
This study determines that, in relation to PEF treatment size and safety, the amount of CTC does not matter once CTC is established with a LAF catheter. These results may extend to “single-shot” catheters where apposition to myocardium, rather than embedding a catheter tip into tissue, is the primary mode of operation21. It is critical to note that both catheter electrode configuration (e.g., electrode spacing, size) and system configuration (e.g., monopolar, bipolar) play important roles in contact dependence. Monopolar modalities have the ability to create deeper lesions for comparable energy outputs relative to bipolar configurations, making them more robust to intermittent contact7. Contact detection systems will need to be harmonized with PEF platforms to ensure appropriate feedback for the catheter design and delivery mechanism.