The psychiаtric mentаl heаlth nurse practitiоner is evaluating a ten year оld patient fоr attention deficit/hyperactivity disorder. An EKG was obtained at the clinic and while reviewing it the nurse practitioner notes a short PR interval and a delta wave, also known as an upstroke of the QRS complex. These EKG findings would lead the nurse practitioner to decide to treat the patient with what medication: