An 82-year old woman is brought to the physician because of a 1-week history of episodes of light-headaches and fainting

[answerhappygod]

An 82-year old woman is brought to the physician because of a 1-week history of episodes of light-headaches and fainting. Her pulse is 45/min, and blood pressure is 90/50 mm Hg. Physical examination shows no other abnormalities. An ECG shows normal, regular P waves followed by normal QRS complexes. The physician decreases the dose of propranolol. Five days later, the patient's pulse is 80/min, and her symptoms have resolved. Which of the following is the most likely explanation for this patient's low pulse while taking the higher dose of propranolol?


A) Decreased activation of fast sodium channels
B) Decreased rate of repolarization phase
C) Decreased slope of diastolic depolarization
D) Increased calciumin flux during latep hase of slowd epolarization
E) Increased potassium influx during rapid depolarization phase
F) Increased sodium efflux during early repolarization phase