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.