2.3 Cryoballoon ablation protocol
After gaining LA access, we injected contrast into the LA to define the
position of each PV ostium. Through a steerable 15-Fr sheath (FlexCath
Advance; Medtronic, Minneapolis, MN, USA), an inner lumen mapping
catheter (Achieve; Medtronic, Minneapolis, MN, USA) was advanced into
each PV ostium. Subsequently, a 28-mm second-generation CB (Arctic Front
Advance; Medtronic, Minneapolis, MN, USA) was advanced over the inner
lumen mapping catheter, inflated, and positioned sequentially in the PV
ostium of each vein. An optimal vessel occlusion was considered to be
achieved upon selective contrast injection from the tip of the CB
showing total contrast retention with no backflow into the LA. Once a
complete occlusion was documented, we withdrew the CB slightly and
allowed leakage around the PV-balloon interface to better define the PV
ostium and ensured a proximal ablation position. We reapplied only the
minimal amount of pressure needed to regain the occlusion before the
ablation, and cryothermal energy delivery was commenced. Standard
cryoenergy applications lasted for 180 seconds. If PV potentials were
visible during freezing energy delivery, the time to PV isolation was
recorded when the potentials completely disappeared or became
dissociated from the LA activity.
When the superior PV was not isolated with CB application even if the PV
was completely occluded, we introduced the CST ablation technique and
advanced the CB into the ipsilateral inferior PV, while the superior PV
potentials were monitored during freezing energy delivery by a Lasso
catheter placed inside the superior PV. When the time to PV isolation
was clearly measured, we used it as a guide in deciding the freezing
duration; we usually added more than 120 seconds to it as long as the
total freezing duration did not exceed 240 seconds. If the superior PV
was isolated during CB ablation to the ipsilateral inferior PV, we
regarded this as successful CST ablation. When PV isolation was not
achieved with CB application only, we performed touch-up ablation of the
PV using an open-irrigated radiofrequency catheter (FlexAbility and
TactiCath; Abbott, Chicago, IL, USA or ThermoCool; Biosense Webster,
Irvine, CA, USA). CB ablation was applied in the following order: LSPV,
LIPV, right inferior PV, and right superior PV (RSPV).
During cryoablation of the right-sided PVs, continuous phrenic nerve
stimulation with a decapolar catheter positioned in the superior vena
cava was performed. The integrity of the phrenic nerve was monitored by
intermittent fluoroscopy, tactile feedback, and right-sided compound
motor action potential (CMAP) monitoring. When the CMAP amplitude
decreased by more than 30% from the control value, CB application was
prematurely terminated to avoid any injury to the phrenic nerve.
During CB ablation, the luminal esophageal temperature was also
continuously monitored using an esophageal temperature probe
(SensiTherm; Abbott, Chicago, IL, USA or Esophaster; Japan Lifeline,
Tokyo, Japan). CB application was stopped when the esophageal
temperature dropped below 15°C.