A client has had a myocardial infarction (MI) that damaged the right atrium, which has interfered with the SA node. The compensatory mechanism, the AV node, becomes the pacemaker of the heart and beats how many times/minute?
A) 10 to 20 beats/minute
B) 21 to 30 beats/minute
C) 45 to 50 beats/minute
D) 55 to 60 beats/minute
Ans: C
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The AV nodal fibers, when not stimulated, discharge at an intrinsic rate of 45 to 50 times a minute, and the Purkinje fibers discharge 15 to 40 times/minute. The SA node has the fastest intrinsic rate of firing (60–100 beats/minute) and normally functions as the pacemaker of the heart. Should the SA node fail to discharge, the AV node can assume the pacemaker function of the heart, and the Purkinje system can assume the pacemaker function of the ventricles should the AV junction fail to conduct impulses from the atria to the ventricles.
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