A junctional escape rhythm occurs because of _____
a. severe chronic obstructive pulmonary disease
b. multiple irritable sites firing within the AV junction
c. slowing of the rate of the heart's primary pacemaker
d. intrathoracic pressure changes associated with the normal respiratory cycle
C
The atrioventricular (AV) junction may assume responsibility for pacing the heart if (1) the sinoatrial (SA) node fails to discharge (such as sinus arrest), (2) an impulse from the SA node is generated but blocked as it exits the SA node (such as SA block), (3) the rate of discharge of the SA node is slower than that of the AV junction (such as a sinus bradycardia or the slower phase of a sinus arrhythmia), and (4) an impulse from the SA node is generated and is conducted through the atria, but is not conducted to the ventricles (such as an AV block).
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