Forest plots of most important secondary outcomes. (A) Relative risk of ablation-associated persistent phrenic nerve palsy in randomized and non-randomized studies. Test for subgroup differences: Z = −0.627 (P = 0.531). Overall heterogeneity: I² = 0.00%. (B) Difference between double freeze and single freeze procedure duration in randomized and non-randomized studies (presented in minutes). Test for subgroup differences: Z = 1.957 (P = 0.050). Overall heterogeneity: I² = 95.72%. 95% CI, 95% confidence interval; RCT, randomized clinical trial; RR, relative risk.