A 58-year-old man with a history of hypertension and recent myocardial infarction presents to the emergency department with palpitations and dizziness. His heart rate is 160 bpm with a regular rhythm. ECG shows a narrow complex tachycardia with a rate of 160 bpm. Blood pressure is 110/70 mmHg. Intravenous adenosine 6 mg is administered, which terminates the arrhythmia within seconds. Which of the following best describes the mechanism of action of adenosine in terminating this arrhythmia?