Study selection
The a priori search strategy identified 3061 articles (Fig. 1) after removing duplicates. Post-preliminary screening using abstracts and applying the exclusion criteria, 2754 articles were excluded. The remaining 307 articles were carefully evaluated (full text) utilising the inclusion criteria, leading to further exclusion of 234 studies.
Study characteristics
A total of 73 studies and 14,148 participants were included, with a mean age of 59 (\(\pm\) 10 SD). They were followed up for 3–61 months and AF recurrence rates varied from 12 to 83%. Raw data comprising baseline characteristics and follow-up for individual studies can be found in Supplementary Table 2. Type of ablation (radiofrequency, cryoballoon), strategy (pulmonary vein isolation, linear lesions, mitral isthmus line, complex fractionated atrial electrograms, cavotricuspid isthmus) and proportions of AF type (PAF, persistent AF, LSPAF) from the individual studies are described in Supplementary Table 3. The 73 articles (Supplementary References) included 22 biomarkers:
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(1)
Natriuretic peptides [atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), N-terminal pro-brain natriuretic peptide (NT-proBNP)],
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(2)
Fibrosis markers [gal-3, CITP, TIMP, transforming growth factor-beta (TGF-β)],
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(3)
Inflammatory pathway markers [tumour necrosis factor-alpha (TNF), CRP, hsCRP, white blood cell (WBC), NLR, IL-6],
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(4)
Lipid profile markers [cholesterol, LDL, high-density lipoprotein (HDL), triglycerides (TG)],
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(5)
Others, such as renal function indicators [creatinine (Cr), eGFR], cardiac injury marker [troponin I (Trop)], uric acid and Haemoglobin A1c (HbA1c).
Natriuretic peptides and association with AF recurrence
Based on five studies involving 324 patients, high levels of baseline ANP were significantly associated with AF recurrence post ablation (OR 1.50, 95% CI: 0.99–2.26, p = 0.05, Fig. 2). There was no statistical heterogeneity (I2 = 0) found for these studies, with no outliers detected. There were 21 studies involving 5008 patients in the meta-analysis for BNP, and the pooled result showed that baseline BNP was significantly higher in patients who experienced AF recurrence post CA compared to those that remained in sinus rhythm (OR 2.91, 95% CI: 1.74–4.88, p < 0.01, Fig. 2). However, the heterogeneity was significantly high (I2 = 95%, p < 0.01) and remained so even when outliers were removed (I2 = 78%, p < 0.01; Supplementary Fig. 1). Fifteen studies were pooled for assessing baseline NT-proBNP levels in 2165 patients. The recurrence group had significantly higher NT-proBNP than the non-recurrence group following ablation (OR 3.11, 95% CI: 1.80–5.36, p < 0.01, Fig. 2). Heterogeneity decreased from 85% to 69% following outlier abstraction. Excluding outliers resulted in diminishing the strength of association of high levels of BNP and NT-proBNP, and AF recurrence (BNP OR 2.14, 95% CI: 1.62–2.83), p < 0.01 and NT-proBNP OR 2.63, 95% CI: 1.77–3.91, p < 0.01, Supplementary Fig. 1).
Inflammatory markers and association with AF recurrence
Based on 21 studies (5049 patients), pooled SMD for baseline hsCRP showed that levels were higher in the recurrence group compared to the non-recurrence group post-ablation (OR 2.04, 95% CI: 1.28–3.23, p < 0.01, Fig. 3). The heterogeneity of these studies was high (I2 = 94%, p < 0.01). Subtracting outliers reduced heterogeneity from high to moderate (I2 = 51%, p < 0.01) with a decreased strength of association of hsCRP and AF recurrence (OR 1.40, 95% CI: 1.15–1.72, p < 0.01, Supplementary Fig. 1). There were 15 studies retrieved for baseline WBC, and levels were higher in patients with AF recurrence post-CA (OR 1.38, 95% CI: 1.09–1.75, p < 0.01, Fig. 3). The heterogeneity of these studies was moderate to high (I2 = 65%, p < 0.01). The magnitude of association reduced from OR 1.38 to OR 1.20 after removing outliers (95% CI: 1–1.44, p = 0.05, Supplementary Fig. 1). Six studies showed that baseline IL-6 levels were higher in patients with recurrence of AF following ablation than those that maintained sinus rhythm (OR 1.83, 95% CI: 1.18–2.84, p < 0.01, Fig. 3). The studies showed very low heterogeneity (I2 = 3%, p = 0.40). There were no outliers identified in studies reporting IL-6.
Other biomarkers and association with AF recurrence
Lipid markers (cholesterol, LDL, HDL and TG), fibrosis/inflammation biomarkers (CRP, NLR, TNF, TGF-β, Gal-3, TIMP), creatinine, troponin I and HbA1c did not show variation in levels between the groups (recurrence vs non-recurrence) following AF ablation (Supplementary Fig. 2, 3, 4, 5). After removing outliers, raised baseline uric acid levels were shown to be associated with AF recurrence following ablation (OR 1.26, 95% CI: 1.01–1.58, p = 0.04, Fig. 4). Three studies reported that baseline CITP values were higher in AF recurrence than the non-recurrence group (OR 1.89, 95% CI: 1.16–3.08, p = 0.01, Fig. 5). The heterogeneity of these studies was low (I2 = 0%, p = 0.39). Only eGFR was present in low levels in the recurrence group compared to non-recurrence in 19 studies (OR 0.68, 95% CI: 0.54–0.86, p < 0.01, Fig. 5). The heterogeneity was high (I2 = 80%, p < 0.01) and decreased after removing outliers (I2 = 25%, p = 0.16; OR 0.78, 95% CI: 0.68–0.90, p < 0.01; Supplementary Fig. 1).
Ranking, meta-regression, sub-group analysis and publication bias
The ranking of biomarkers and their association with AF recurrence was based on pooled ORs. The highest ORs were detected for NT-proBNP (3.11), BNP (2.91), hsCRP (2.04), CITP (1.89) and IL-6 (1.83). Meta-regression analysis was conducted for biomarkers with 10 or more studies (BNP, NT-proBNP, hsCRP, WBC and eGFR) to explore sources of heterogeneity (Supplementary Table 7). As expected, AF type emerged as an important factor contributing to heterogeneity (R2 = 55.74%, p < 0.0001) in BNP analysis. We conducted subgroup analyses (Supplementary Fig. 6), which showed that studies (six) including only paroxysmal AF (PAF) patients showed that levels of BNP were significantly higher in the recurrence group (OR 2.74, 95% CI: 1.63–4.60, p < 0.01, I2 = 78%, p < 0.01). Despite statistical significance, there is a decrease in strength of association of high level of BNP and AF recurrence for studies that included both PAF and persistent AF cohorts [OR 1.95, 95% CI: 1.15–3.31, p < 0.05 (I2 = 85%, p < 0.01)]. The addition of long-standing persistent AF populations (3 studies) to PAF and persistent AF showed no statistical difference in BNP levels in the groups of AF recurrence and non-recurrence. Egger’s test (p > 0.05) did not illustrate funnel plot asymmetry indicating there was no small-study effect for all the biomarkers that retrieved 10 or more studies (BNP, NT-proBNP, hsCRP, WBC and eGFR; Supplementary Fig. 7).
Risk of bias in studies
The majority of studies were considered to have a low to moderate (58 articles) risk of bias (Supplementary Table 8). Of the 15 studies classified as having a high risk of bias, none were excluded from the analysis.