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.