Final answer:
The most important nursing action when planning care for a type 1 diabetic client with heart failure on digoxin is to monitor the client for cardiac dysrhythmias, as digoxin affects heart conduction and diabetes may alter drug interactions. Therefore, the correct option is b.
Step-by-step explanation:
When a client with type 1 diabetes develops heart failure and digoxin is prescribed, an important nursing action to include when planning care is to monitor the client for cardiac dysrhythmias. This action is crucial because digoxin can affect the electrical conduction system of the heart, and patients with diabetes may have altered pharmacokinetics that could enhance their risk for dysrhythmias. It's also important to note that while digoxin and insulin therapies can coexist, one does not necessarily directly impact the dosage of the other. Monitoring blood glucose levels will also still be essential since type 1 diabetes requires careful management of insulin to maintain proper blood glucose levels, and hypoglycemia or hyperglycemia can occur for various reasons as outlined in the referenced information.