A sudden, substantial increase in efferent vagal activity (induced by carotid sinus massage, for example) would: a. strengthen the contraction of atrial myocytes. b. strengthen the stimulatory action of any concurrent sympathetic activity. c. increase the speed of impulse conduction in the ventricular Purkinje fibers. d. decrease the heart rate within one or two cardiac cycles. e. shorten the AV conduction time.
