Directed acyclic graphs helped to identify confounding in the association of disability and electrocardiographic findings: results from the KORA-Age study.

OBJECTIVES:To examine the association between electrocardiographic (ECG) findings and disability status in older adults. STUDY DESIGN AND SETTING:KORA-Age, a population-based cross-sectional study of the MONICA/KORA project, a randomized sample from Southern Germany of people aged 65 years or older. RESULTS:A total of 534 (51.5%) of 1,037 participants were characterized as disabled. Disabled participants were on average 4.5 years older than those who were not disabled. Crude associations of left-axis deviation, ventricular conduction defects, atrial fibrillation, and QT prolongation with disability status were significant (P < 0.05). In models controlled for age and sex, these effects remained constant except for QT prolongation. In the models adjusted for the minimal sufficient adjustment set (consisting of the variables sex, physical activity, age, obesity, diabetes, education, heart diseases, income, lung diseases, and stroke) identified by a directed acyclic graph (DAG), no significant association could be shown. CONCLUSION:Associations between specific ECG findings and disability were found in unadjusted analysis and logistic models adjusted for age and sex. However, when adjusting for other possible confounders identified by the DAG, all these associations were no longer significant. It is important to adequately identify confounding in such settings.