Final answer:
The medication that should be withheld before elective cardioversion for supraventricular tachycardia, from the provided options, is usually digoxin. This drug can increase the risk of arrhythmias following the procedure.
Step-by-step explanation:
A nurse preparing a client for elective cardioversion to treat supraventricular tachycardia should instruct the client to withhold certain medications that may affect the procedure. Of the options listed, the medication that should typically be withheld before cardioversion is digoxin, especially if the client has signs of digoxin toxicity or if their digoxin levels are high. Digoxin, a cardiac glycoside with positive inotropic effects, can increase the risk of arrhythmias following cardioversion. It is important to follow the cardiologist's specific instructions, as they may have different protocols based on the individual patient's condition.
Medications such as enoxaparin are anticoagulants, or blood thinners, and their use around the time of cardioversion is typically to reduce the risk of thromboembolic events. Stopping them would require careful consideration and weigh the risk of thrombosis. Metformin is used for the treatment of diabetes and diazepam is a benzodiazepine; neither is typically required to be withheld for 48 hours before cardioversion unless specified by a physician for other reasons.