Eligible studies
For the most precise study selection, each database was scanned through combination of two key words: (1) cryoballoon ablation ANDphrenic nerve injury and cryoballoon ablation ANDcompound motor potential action OR (2) CMAP . Initially, 301 potentially relevant articles were identified according to the adopted search strategy. As illustrated in the flow diagram (Fig. 1), the first review excluded 216 papers based on screening the titles and abstracts, and an additional 21 articles were excluded after a detailed evaluation in addition to 64 articles thoroughly enrolled with timeline and centers origin with intermeshing of records. Finally, 48 eligible observational controlled and noncontrolled trials that fulfilled all inclusion criteria for PNI registry [2,5–17,20–60] Figure 1. For metanalysis of PN protection, location of PNI, and time to resolution of PNI, different criteria ware used; thus, a significantly less papers met the final criteria, and each part of the analysis was estimated separately. Nevertheless, the method and equipment of CBA is unified so that they can be analyzed together and in dependent subgroups.
The studies included in this meta-analysis were published between September 2008 [21] and May 2019 [60]. Two randomized controlled trials met the inclusion criteria [54,57]. The reasons for final exclusion were lack of essential clinical outcome data, repeated records in databases, review articles, duplicated studies, and non-controlled trials. As to the quality of those included studies forty-eight full-text studies were allocated a NOS score of ≥ 7 [19].