Systems and methods are provided for determining an estimated risk of arrhythmia during or after dialysis based on changes in serum potassium concentration of a patient and an amount of fluid removed from the patient during dialysis. The systems and methods allow for a determination of a risk that arrhythmia will occur due to the changes in potassium and fluid volume of a patient during dialysis, and for optimizing a dialysis prescription in order to minimize the risk of arrhythmia.