In this population-based prospective study, we found that kidney damage, manifested as micro-or macroalbuminuria, and decreased kidney function were associated with a higher AF risk. An elevated risk of AF was observed even among individuals with mildly decreased kidney function measured by eGFR
cys. These associations were independent of lifestyles, clinical factors, and cardiovascular disease, and were similar in men, women, whites, and African-Americans, and in individuals with or without a history of cardiovascular disease or hypertension, and among those taking antihypertensive medications. The somewhat different results using eGFR
cys and eGFR
creat are consistent with previous data suggesting that the former presents a more linear association with mortality, probably due to creatinine being lowered by muscle loss.
30Previous studies addressing the relationship of kidney function with AF risk have provided inconsistent results. Lower eGFR
creat was associated with a higher risk of AF in two studies in Japan.
14, 31 However, reduced kidney function as measured by both higher cystatin C levels or reduced eGFR
creat was not associated with AF risk in the Cardiovascular Health Study, a population-based study of elderly individuals in the US.
16 Potential explanations for the discrepancy with our results is the older age in the Cardiovascular Health Study (average 75 vs. 63 in the ARIC study), differences in the classification of kidney dysfunction (cystatin C quartiles in the Cardiovascular Health Study vs. clinical categories of eGFR
cys in our analysis), and in AF ascertainment.
16 In a subset of participants in the prospective Framingham Heart Study, ACR was not associated with AF incidence; however their analysis had limited statistical power as it only included 135 AF events.
15 In contrast, cross-sectional analyses have consistently shown a higher prevalence of AF among individuals with chronic kidney disease.
11–13 Our study compares favorably with previous reports in its large sample size, extended follow-up, and well characterized information on potential confounders.
CKD may increase the risk of AF through several mechanisms. Individuals with kidney dysfunction are more likely to develop hypertension and have poorer control of their blood pressure.
32 The resulting expansion of the extracellular fluid might lead to left ventricular hypertrophy, poor ventricular compliance and, eventually, to atrial stretch and fibrosis, established predictors of AF.
5, 33 In addition, CKD leads to pathological activation of the intrarenal RAA system.
34 Compelling evidence suggests that an upregulated RAA system causes atrial fibrosis and electrical remodeling, creating the required substrate for the development of AF.
35 This effect might be partly mediated through increased secretion of TGF-β1, which is pro-fibrotic.
36 Moreover, involvement of the RAA system in AF pathogenesis is also suggested by the potential reduced risk of AF after use of ACEIs or ARBs,
35, 37 though this has not been observed in all studies.
38 Whether CKD affects AF risk through this mechanism merits further inquiry. Finally, CKD might cause AF through an increased risk of cardiovascular disease, including heart failure and CHD,
1, 2, 5 or through sympathetic overactivity.
8 Our observation that both low eGFR
cys and presence of albuminuria independently increased the risk of AF hints that a variety of mechanisms underlie these associations.
Some study limitations should be noted. In our primary analysis, incident AF was mostly identified from hospitalization discharges; therefore, we could not include asymptomatic AF and AF managed exclusively in an outpatient setting. However, an analysis including only AF events identified from systematic study ECGs found an association between CKD and AF risk of similar magnitude. Moreover, we and others have previously shown that the validity of AF ascertainment using hospitalizations is acceptable,
22, 39 that incidence rates of AF in the ARIC Study are consistent with other population-based studies,
22 and that the associations between variants in the chromosome 4q25—extremely specific for AF risk—and AF incidence in ARIC are similar to those in other studies with a more intensive ascertainment of AF.
40 Still, individuals with reduced renal function may have been more likely to have their AF detected by hospitalization than those with normal function, potentially creating ascertainment bias. Other important limitations include the absence of echocardiographic data, the potential for residual confounding by some CKD risk factors (e.g. hypertension, diabetes), the availability of only 1 measurement of ACR and cystatin C, which could lead to measurement bias, and the lack of standardization of cystatin C assays and equation. Despite some limitations, our study has important strengths: a large sample size, the elevated number of AF events, the long follow-up, the diversity of the study population, and the quality and extent of measured covariates.
In conclusion, we have found that kidney damage and impaired kidney function are associated with an increased risk of AF independently of other risk factors. Given the growing burden of CKD in the general population and the potential for its prevention,
41 future studies should focus on understanding the specific mechanisms underlying this association. Furthermore, strategies for the prevention of AF will have to consider CKD as a preventable risk factor for AF in addition to other well-established risk factors.
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