What is the rate of the Bundle of His/Purkinje fibers?

The Bundle of His and Purkinje fibers play a critical role in the conduction system of the heart. They are responsible for transmitting electrical impulses from the atrioventricular (AV) node to the ventricles, facilitating coordinated contraction. The intrinsic firing rate of these structures is key to understanding their function when the heart relies on them as a pacemaker due to dysfunction in the primary pacemaker cells, which are located in the sinoatrial (SA) node.

The Bundle of His/Purkinje fibers typically exhibit a firing rate of approximately 20 to 40 beats per minute (BPM) under normal circumstances, which is considerably lower than the rates found in primary pacemaking structures such as the SA node (60-100 BPM). However, if the SA and AV nodes fail to effectively drive heart rate, the Purkinje fibers can increase their rate to a range of 30 to 50 BPM to maintain some level of cardiac output, but this is not typical.

In clinical practice, it is acknowledged that when the Purkinje system becomes the dominant pacemaker due to higher-level pacemaker failure, the heart could achieve frequencies exceeding 40 BPM. Hence, recognizing that the Purkinje fibers can indeed fire above their intrinsic rate