A 29 year old woman who has a 5-year history of long-lasting palpitations has had two syncopal episodes in the last 3 months. Her ECG at rest shows slow irregular atrial activity (HR 52/min), a normal PR interval and normal QRS complexes. A diagnosis cannot be made unless an invasive electrophysiologic study is done. which of the following is the most likely site of the patient abnormality? a) SA node b) Right bundle branch c) Left bundle branch d) Bundle of HIS e) AV node.