Discussion:
In this study, we focused on a selective group of AF patients who underwent ablation. By comparing the eGFR before RFCA to the eGFR during readmission for recurrence, we found that renal function could still be improved after RFCA in NVAF patients with a mildly decreased eGFR, even if they had recurrent atrial arrhythmia.
Among general populations, the annual decline in eGFR is between 0 and 1 ml/min/1.73 m2 for both sexes after the age of 20-30 years according to the NKF guidelines.25 In chronic kidney disease (CKD) patients, the average decline rate is 1-2.5 ml/min/1.73 m2.26 In patients with additional comorbidities in addition to CKD, the decline rate has been observed to be 2.16 and 2.07 ml/min/1.73 m2 per year in men and women, respectively.27 In patients with both AF and CKD, the incidence of progression to end-stage renal disease is substantially higher than that in patients without AF.7 Previous studies have shown that CKD patients free from AF after RFCA had better renal function.19,21,22 Our study, on the other hand, showed that patients with mildly impaired renal function (eGFR of 60 to 89 ml/min/1.73 m²) could achieve improved renal function even with atrial arrhythmia recurrence after RFCA. Moreover, the absolute eGFR has a closer association with the CHA2DS2-VASc score and the type of recurrent atrial arrhythmia than the initial CHA2DS2-VASc score or AF type, which presumptively could be partially attributed to the reduced AF burden after RFCA.
Cardiovascular diseases and CKD are concordant. The results from previous studies indicate that the treatment of concomitant cardiovascular diseases could slow the progression of renal function deterioration. The mainstay to slow the progression of renal function deterioration is to control comorbidities, such as heart failure, hypertension and diabetes mellitus. 28 As a practical tool to stratify stroke risk in NVAF patients, the CHA2DS2-VASc score is highly recommended for use by existing guidelines.29 This score is the sum of cardiovascular risk factors that a patient may have. Stroke risk in NVAF patients has recently been considered a dynamic process due to increases in age and other new incident risk factors. Therefore, the change in score between baseline and follow-up, which was reflected by CHA2DS2-VASc, could have greater value in predicting ischemic stroke. Our study shows that a lower CHA2DS2-VASc score was a significant factor associated with improved renal function, which suggests that controlling comorbidities should still be of great importance even after RFCA.
The AF burden, which means the amount or quantity of AF a patient has, is often expressed as the percent time of atrial fibrillation divided by total monitoring time, representing the duration patients are in an AF state. AF burden is an emerging parameter that has a close relationship to cardiovascular outcomes.30,31 In addition, some studies suggest that a higher AF burden could increase the risk of stroke.32
Catheter ablation is considered to be an effective treatment for reducing AF burden.12,33 However, the endpoint of successful AF ablation has long been reflected as no atrial arrhythmia lasting longer than 30 s captured by a monitoring device. Based on this threshold, the cumulative recurrence rate at 5 years after AF ablation ranges from 60% to 73%.34 Recently, after the results of the CABANA study were released, the adoption of catheter ablation for AF patients has been questioned.10 The crux of the argument focused on whether this binary evaluation of AF recurrence could reflect the total advantages of catheter ablation. In the CASTLE AF study, the AF recurrence rate in the ablation group was 36.9% after 60 months of follow-up. Furthermore, the AF burden was reduced from 51% to 20% in the ablation group but remained at more than 50% in the pharmacologic group at the 12-month follow-up.12 In addition, the post hoc analysis of the CABANA trial showed that AF burden decreased by 69-88% in the ablation group and 48-73% in the medical therapy group after 5 years (P< 0.01).17 In the CIRCA-DOSE trial, the one-year success rate of AF ablation was 53%, and the AF burden was relatively reduced by nearly more than 98%.35
It is unclear whether AF burden has a relationship with renal function impairment. However, several studies have shown that maintaining sinus rhythm is associated with better renal function, which implies that patients with renal dysfunction might benefit from reduced AF burden.19,21,22 To evaluate the effect of AF burden on renal function, the pattern of arrhythmia change before and after the index ablation was classified into 4 groups in our study. The recurrence of paroxysmal or nonparoxysmal arrhythmia could roughly represent different AF burdens. Based on the results from our study, for AF patients with a reduced eGFR, considering the protection of renal function, clinicians should pay more attention to heart rhythm monitoring and timely conversion to sinus rhythm with medical therapy or catheter ablation. Moreover, our study provides another angle to look at the benefits of AF catheter ablation. In patients with mildly impaired renal function, even those with recurrence, after a mean follow-up of 11 months, renal function could still be improved after catheter ablation. This could be informative for clinicians referring patients for treatment. AF ablation could lead to a better outcome by reducing AF burden instead of eliminating AF completely in a selective group of patients.
Our study had some limitations. Although we demonstrated the relationship between changes in eGFR and recurrent arrhythmia types, we were not able to verify how AF burden changes would affect renal function due to a lack of precise data on AF burden. Second, renal function in this study was evaluated by eGFR alone. Other measurements of renal function, such as proteinuria, were not used in this study. Third, this is a single-arm self-control study that aimed to reveal the change in renal function before and after RFCA. No real control group was recruited in this study. Finally, the increase in eGFR was modest, and the clinical effect of the eGFR change is still unknown.
In conclusion, in NVAF patients with mildly impaired renal function, even those with recurrence after the initial catheter ablation, we observed improvements in renal function, which was associated with a lower CHA2DS2-VASc score and paroxysmal arrhythmia.