Final answer:
In the event that the SA and AV nodes fail to initiate impulses, the heart will continue to beat due to subsequent pacemakers in the conduction system, with the atrioventricular bundle setting a rate of 30-40 bpm, bundle branches at 20-30 bpm, and Purkinje fibers at 15-20 bpm.
Step-by-step explanation:
If both the SA and AV nodes fail to initiate impulses, the heart would still be able to generate a heartbeat due to the presence of the atrioventricular bundle, bundle branches, and Purkinje fibers. These lower components of the conduction system can act as pacemakers, though they do so at a slower rate.
If the AV node were blocked or unable to function, the atrioventricular bundle would generate heartbeats at a rate of approximately 30-40 beats per minute. The bundle branches would provide a rate of 20-30 beats per minute, and finally, the Purkinje fibers would maintain a rate of 15-20 beats per minute. In the case of a third-degree AV block, where there is no correlation between the P waves and QRS complexes in an ECG, the ventricles would beat at the intrinsic rate provided by the AV node or the lower pacemaker cells, if the AV is also non-functional.