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.