Results
During this study, 94 structures were ablated in 25 healthy animals
including 23 swine, 1 canine, and 1 ovine. The targeted structures
included: RA (5), LA posterior wall (2), RAA (6), LAA (14), right
superior PV (22), right inferior PV (20), left PV (16), SVC (4) and IVC
(5). Each structure was ablated using 1.1±0.2 PFA applications resulting
in successful ablation/isolation (Figure 3). Real-time
locations of the spiral PFA catheter during ablation were recorded
within the 3D map (Figure 4). Given the advent of QRS gating,
no ventricular arrhythmias were inadvertently triggered during PFA.
Meanwhile, PFA resulted in marked reduction in the post- versus pre-PFA
electrogram amplitudes (0.17±0.21 mV vs. 1.18±1.08 mV;
P<0.0001) as well as a significant increase in the post-
versus pre-PFA pacing threshold at the ablated sites (>15
mA versus 0.6±0.7 mA, P<0.001) (Table 1). Minimal
microbubbling and no discernable skeletal muscle twitching was observed
during PFA. Though administration of an intravenous paralytic agent
(succinylcholine 1 mg/kg) temporarily abolished all forms of skeletal
muscle twitch/activation; in the absence of a paralytic agent, PFA at
sites adjacent to the right/left PN (e.g., lateral RA or LAA)
commonly resulted in visible PN capture and hemi-diaphragmatic
stimulation. Yet, there was no incidence of diminished PN function
during or post-PFA as confirmed by low-output PN pacing capture using
the PFA catheter. When PN pacing capture was present (e.g., when
targeting the right superior PV), acceleration levels were measured in
the range of 5–9 m/s2. When ablating structures
remote from the right/left PNs (e.g., the left PV), the absolute
mean acceleration was only 0.05 m/s2 which was
indiscernible from the background noise level (Supplemental
Figure).
Complete and durable conduction block was demonstrated acutely and up to
3 months post-PFA (Figure 5). All lesions were large and
durable at follow-up (range: 3 weeks to 3 months). Histologically, the
PFA lesions were contiguous and transmural (Figure 6),measuring 25±9 mm x 21±7 mm and 7.6±1.6 mm deep. No evidence of
collateral injury or abnormalities involving the PN (Figure 6)could be detected in any of the animals, including the 8 swine in which
the PNs were intentionally targeted – neither acutely, nor during
follow-up at 3–4 weeks post-PFA. Additionally, there were no observed
cases of vascular injury. Likewise, gross and microscopic examinations
of the brain, the rete mirabile, the kidneys, the liver, the lungs, and
the bronchi revealed no evidence of embolization or adjacent
structure/tissue injury in any of the animals (Figure 7).Moreover, post- versus pre-PFA T2-weighted MRI scanning (n=3 swine) did
not show any evidence of embolic events.
In 5 swine (62 ± 12 kg), 14 PFA applications were delivered within the
IVC toward an opposing esophagus, intentionally deviated toward/adjacent
to this structure. All 14 animals completed the follow-up period without
clinical sequelae. Their body weights increased by 15±4% during
follow-up. All IVC treatments were transmural, measuring 15.6±5.5 mm x
5.9±1.4 mm. Histopathologic examinations revealed acute PFA-related
changes in the esophageal muscular layer which appeared within 2 h of
PFA (Figure 8). However, these changes completely resolved by
21±5 days of follow-up. No other acute or chronic lesions/abnormalities
were detected in the esophageal mucosa or submucosa in any of the 5
animals at 3 weeks of follow-up.