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What is the intrinsic firing rate of the ventricles?

  1. 40-60 bpm

  2. 60-80 bpm

  3. 20-40 bpm

  4. 80-100 bpm

The correct answer is: 20-40 bpm

The intrinsic firing rate of the ventricles typically refers to the rate at which the ventricular pacemaker cells (such as the Purkinje fibers) generate impulses in the absence of external stimuli. This intrinsic rate is generally in the range of 20 to 40 beats per minute. This firing rate is significantly lower than that of other components of the conduction system, like the sinoatrial (SA) node, which normally generates impulses at a rate of 60 to 100 bpm — making it the primary pacemaker of the heart. When higher-level pacemakers, like the SA node or atrioventricular (AV) node, are not functioning properly, the ventricles can take over as a backup pacemaker, but at this slower rate. Understanding the intrinsic firing rate and the hierarchy of pacemaker activity in the heart is crucial for comprehending various cardiac conditions, such as bradycardia or heart blocks, where the normal conduction pathways are interrupted.