Introduction
Since 2006, the cryoballoon ablation (CBA) technique has revolutionized the treatment of paroxysmal atrial fibrillation and has become the gold standard treatment method since 2012. The main reason behind its efficacy is its simplifying pulmonary vein (PV) isolation, making it a highly standardized and reproducible procedure [1–3]. Nevertheless, CBA is associated with a significant risk of right phrenic nerve injury (rPNI) because of the proximity between the right phrenic nerves and the right-sided PVs during balloon-based ablations [4]. PNI can be transient or persistent, and that feature depends on the time to recovery. Transient phrenic nerve paralysis/injury (TPNI) is defined either as completely resolved before the end of the procedure [5,6], lasting less than 24 hours [7], or until discharge as demonstrated by chest fluoroscopy [8]. Any longer period of diaphragmatic paralysis is defined as persistent or sustained phrenic nerve injury (PPNI). In a systematic review, the reported incidences of transient and persistent PNI resulting from ablation with the first-generation CB were 6.48% and 4.73%, respectively [9]. The risk of PNI associated with the second-generation CB is even higher with a reported incidence of transient and persistent PNI being 16.0%–24.7% and 5.4%–7.0%, respectively [10–13]. The anatomical relationship of the relevant structures makes the risk unavoidable; however, various techniques have been implemented throughout the last decade for preventing prolonged rPNI [14]. The most used technique involves the use of compound motor action potentials (CMAP). The first record of CMAP was published in 2011 by Franceschi [15]; later, two studies, including multiple patients, were published in 2014 with a significant PPNI reduction [16,17].
In this article, we aimed to perform a systematic review of PNI based on all cryoballoon generations from the last 12 years by conducting a meta-analysis to assess the efficacy of diaphragmatic stimulation and CMAP use for PNI protection. Intra-operative physical conditions both with and without right dome diaphragmatic stimulation and time to recovery data were collected.