A 48-year-old male is evaluated for a 6-month history of intermittent palpitations with accompanying lightheadedness and near syncope. The episodes last approximately 5 minutes and occur once or twice per week. Which of the following is the most appropriate next step in the evaluation of this patient?
a) Ambulatory electrocardiogram (Holter monitor)
b) Exercise stress test
c) Transthoracic echocardiography
d) Cardiac catheterization