Fig. 1

A schematic overview of the study design. A Comparison of observational studies and Mendelian randomization studies to help understand causality from serum electrolyte levels to high risk of AF. AF, atrial fibrillation; SNP, single-nucleotide polymorphism. B Mendelian randomization use genetic variant associated with exposure to estimate the causal effect of the exposure on the outcome. The three core assumptions are: [1] the genetic variant must be strongly associated with the exposure; [2] the genetic variant should be independent of any measured and unmeasured confounders; and [3] the genetic variant must influence the outcome through the exposure only and not through any direct or alternative pathways