Discussion
From the very beginning of the CBA procedure, PNI was associated with right-sided pulmonary vein isolation. No CBA registry in literature without PNI can be found, and every comparison or meta-analysis between RF ablation and cryo-registry shows a disadvantage in this field [6,24,31,37,41,43,49,63,64]. The reason for this issue is a combination of the right phrenic nerve course and cryo-energy dispersion delivered during the procedure [4,65]. Any assessment of distance between PVI ostium and PN may only alert for potential, upcoming complications [4]. Nevertheless, PNI complication is heterogeneous. From our perspective, TPNI (5.7%), resolving until the end of the procedure is a mild complication resulting incomplete or short time vein isolation and up to the day of discharge, also requires an additional X-ray. The serious problem occurs with PPNI (1.9%) that extends beyond the hospital discharge. Most patients have no symptoms during rest, whereas physical activity induces symptoms, such as dyspnea [66,67]. The time for PNI resolution varies significantly. Most can take up to six months to resolve, and almost all are resolved by 12 months. Patients with PPNI need regular checkups and fluoroscopic or sonographic evaluation [64]. We conducted that the first-generation of CB (CB-1) 23 mm CB-1 (deeper seating), which increased the risk of PNI almost three-fold [9]. In the second-generation CBA, a redesigned cooling area caused an increase in the incidence rate, reaching almost 20% overall in some trials [2,10,33,37,57]. Various anatomical predictors were proposed for preventing PNI [68]. The CMAP presented by Franceschi [15] can be called a game-changer by decreasing the amount of persistent PNI. After implementing this method, the PNI decreased significantly from 2.3 to 1.1%. Monitoring diaphragmatic CMAP during phrenic nerve injury capture allows earlier detection of phrenic nerve dysfunction [15, 30,36]. The mean difference in time to PNI between CMAP and the non-CMAP group was shorter, and the temperature was higher, thus causing a benign injury. Lower temperatures and longer applications caused an increase in the risk of PNI, which was also observed by other authors [48]. Analysis of cycle length of phrenic nerve stimulation with the impulse strength did not reveal any statistical favorites; however the Okishige et al. proved that the PNI manifested earlier with weaker power of stimulation [53].
Nevertheless, no technique eliminates the risk of PNI associated with CBA. From this record, long, persistent PNI lasting beyond the time of observation have been reported with and without CMAP [34,35,47,48]. Finally, the amount of PPNI with CMAP decreased and the median time to resolution was shortened from six to three months. This meta-analysis summarizes the findings that CMAP should be obligatorily implemented during each CBA.