| Purkinje fibers | |
|---|---|
 Isolated heart conduction system showing Purkinje fibers | |
 TheQRS complex is the large peak. | |
| Details | |
| Identifiers | |
| Latin | rami subendocardiales |
| MeSH | D011690 |
| TA98 | A12.1.06.008 |
| TA2 | 3961 |
| FMA | 9492 |
| Anatomical terminology | |
ThePurkinje fibers, named forJan Evangelista Purkyně, (English:/pɜːrˈkɪndʒi/pur-KIN-jee;[1]Czech:[ˈpurkɪɲɛ]ⓘ;Purkinje tissue orsubendocardial branches) are located in the innerventricular walls of theheart,[2] just beneath theendocardium in a space called the subendocardium. The Purkinje fibers are specialized conducting fibers composed ofelectrically excitable cells.[3] They are larger thancardiomyocytes with fewer myofibrils and manymitochondria. They conductcardiac action potentials more quickly and efficiently than any of the other cells in the heart'selectrical conduction system.[4] Purkinje fibers allow the heart's conduction system to createsynchronized contractions of its ventricles, and are essential for maintaining healthy and consistentheart rhythm.[5]
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Purkinje fibers are a uniquecardiac end-organ. Furtherhistologic examination reveals that these fibers are split in ventricles walls. The electrical origin of atrial Purkinje fibers arrives from thesinoatrial node.
Given no aberrant channels, the Purkinje fibers are distinctly shielded from each other bycollagen or thecardiac skeleton.
The Purkinje fibers are further specialized to rapidly conduct impulses (having numerous fastvoltage-gatedsodium channels andmitochondria, and fewermyofibrils, than the surrounding muscle tissue). Purkinje fibers take up stain differently from the surrounding muscle cells because of having relatively fewer myofibrils than other cardiac cells. The presence of glycogen around the nucleus causes Purkinje fibers to appear, on a slide, lighter and larger than their neighbors, being arranged along the longitudinal direction (parallel to the cardiac vector). They are oftenbinucleated cells.[6]
Heart rate is governed by many influences from theautonomic nervous system. The Purkinje fibers do not have any known role in setting heart rate unless theSA node is compromised (when they can act aspacemaker cells).[7] They are influenced byelectrical discharge from the sinoatrial node.
During theventricular contraction portion of thecardiac cycle, the Purkinje fibers carry the contraction impulse from both the left and rightbundle branch to themyocardium of the ventricles.[5] This causes the muscle tissue of the ventricles to contract. This generatesforce to ejectblood out of the heart, either to thepulmonary circulation from the right ventricle, or to thesystemic circulation from the left ventricle.[8]
Purkinje fibers also have the ability of firing at a rate of 20–40 beats per minute if upstream conduction or pacemaking ability is compromised.[9] In contrast, the SA node in normal state can fire at 60-100 beats per minute.[9] In short, they generateaction potentials, but at a slower rate than thesinoatrial node.[9] This capability is normally suppressed. Thus, they serve as the last resort when other pacemakers fail. When a Purkinje fiber does fire, it is called apremature ventricular contraction or PVC, or in other situations can be aventricular escape.
Purkinje fibers are named after theCzech scientistJan Evangelista Purkyně, who discovered them in 1839.[10]
