The present study demonstrated a high prevalence and incidence of AF in patients with CKD stage 4–5. By the end of the follow-up period a third of the patients had been diagnosed with AF. Older age, elevated TnT and increased LAVI assessed from transthoracic echocardiography independently predicted the occurrence of new-onset AF in the study patients.
Our study demonstrated for the first time the association between AF incidence and elevated TnT or increased LAVI in patients with CKD stage 4–5. While older age and greater left atrial diameter have been linked to AF incidence in CKD patients in previous studies, there are no prior data on the association between TnT or LAVI and AF incidence in patients with CKD stage 4–5 (9). Reasons for higher troponin levels in new-onset AF patients remain unknown. However, these findings have important clinical implications in AF prediction in the CKD population. In fact, our results suggest that almost every other CKD stage 4–5 patient with TnT > 50 ng/l and LAVI > 30 ml/m2 was at risk for developing new-onset AF within 4 years, and the risk among patients aged over 60 years was even higher (~ 60%). Conversely, only 3% of patients with new-onset AF had TnT ≤ 50 ng/l and LAVI ≤ 30 ml/m2 (Fig. 3).
The association between elevated high-sensitivity troponin and incidence of new-onset AF in CKD patients was explored in a recent study but the cohort comprised patients with only mild to moderate CKD (11). Nevertheless, elevated TnT and increased LAVI are common findings in CKD patients and associated with the risk of left ventricular hypertrophy and heart failure – predictors of AF themselves (12–15). Thus, measurement of TnT and LAVI especially in elderly CKD patients might be reasonable in predicting AF.
Nearly one fifth of the study patients had a prior diagnosis of AF and this was in line with previous reports on CKD patients (7, 8). Older age and dilatation of the left atrium were associated with the history of AF in our study and have consistently predicted AF prevalence in CKD patients irrespective of dialysis treatment in previous studies. Other consistent predictors for positive AF history have been congestive heart failure and male sex (7, 8, 16).
The incidence rate of AF was remarkably high in our study compared to previous studies – even those on dialysis patients. This might be partly explained by the high prevalence of hypertension in our study compared to previous reports (5, 9, 12). Furthermore, two thirds of the patients with new-onset AF were receiving RRT at the time of AF detection. In fact, hemodialysis procedure itself has been identified as a trigger for AF (17). Studies comparing the incidence rate of AF in non-dialysis and dialysis patients with CKD do not exist, but AF incidence has been numerically higher in CKD patients undergoing dialysis (5, 9, 11–13). One previous trial reported a higher incidence rate of AF in dialysis patients compared to healthy controls (13).
Interestingly, most new-onset AF cases were detected during hospital treatment and in two thirds of the patients a predisposing condition was identified (Table 3). The figure is higher compared to previous studies and the most common predisposing condition in our study was infection (33%) while in the study by Lubitz et al most new-onset AFs with a predisposing condition were triggered by surgery (50%) (18). These findings are possibly explained by the relative lability of CKD patients due to the high burden of comorbidities and shared risk factors with AF as well as susceptibility to infections, fluid overload and electrolyte imbalance compared to patients without CKD (19–21). These data suggest that CKD patients recovering from a major surgery or suffering from an acute infection might benefit from screening of AF.
This study has the limitations of an observational study. The study sample of patients was relatively small and the echocardiography data was partly incomplete. However, the patients were extensively and consistently examined by the same clinicians and the quality of the data is high. Some new-onset AF episodes may have been missed since AF is commonly asymptomatic. Nevertheless, all the study patients resided in the catchment area of the research hospital and all AF episodes are recorded in the patient registry of the same hospital. Despite these limitations, we believe that these data can benefit clinical practice and guide future research.