An elderly patient on digoxin develops new onset atrial fibrillation. What should be the most appropriate initial intervention?

The most appropriate initial intervention in this scenario is to order a serum TSH, digoxin level, and an electrolyte panel.

In elderly patients taking digoxin, the development of new onset atrial fibrillation can be indicative of underlying issues that might be contributing to the arrhythmia. Evaluating thyroid function through serum thyroid-stimulating hormone (TSH) is essential, as thyroid disorders, particularly hyperthyroidism, are known to cause atrial fibrillation.

Additionally, measuring the digoxin level is crucial to ensure that the patient is not experiencing digoxin toxicity, which can also present with arrhythmias. Electrolyte imbalances, such as low potassium or magnesium, can exacerbate cardiac problems and lead to arrhythmias, including atrial fibrillation. Therefore, checking an electrolyte panel is vital in assessing the patient's current status and guiding further management.

In contrast, other options may not address the immediate need for a comprehensive assessment of the patient's condition. Discontinuing digoxin therapy could potentially lead to worsening heart failure if the patient requires ongoing treatment for that condition. Simply decreasing the digoxin dose does not assess the potential causes of the new atrial fibrillation and could also risk the patient remaining on an inappropriate therapeutic dose.