Purkinjefibers

Purkinje fibers are specialized conducting myocardial fibers that form the terminal components of the heart's His-Purkinje system. They originate from the bundle of His and spread through the subendocardial layer of the ventricles, creating a network that reaches into both the left and right ventricular walls. The cells are larger and paler than ordinary cardiomyocytes, with sparse contractile elements and abundant glycogen, and they have extensive gap junctions to promote rapid electrical coupling with surrounding ventricular muscle.

Functionally, Purkinje fibers rapidly conduct electrical impulses from the AV node through the bundle branches to the ventricular myocardium, enabling nearly synchronous contraction of the ventricles. They possess one of the fastest conduction velocities in the heart, typically about 2–4 meters per second, which helps coordinate the timing of ventricular depolarization and contraction.

In addition to fast conduction, Purkinje tissue can exhibit automaticity under certain conditions, acting as a latent pacemaker if the sinoatrial or atrioventricular nodes fail. This property contributes to escape rhythms, though it is usually slower than the primary pacemakers of the heart.

Clinical relevance centers on the Purkinje network’s role in arrhythmias. Purkinje fibers can participate in ectopic ventricular activity and reentrant circuits, particularly after myocardial infarction or in certain cardiomyopathies, and may be involved in triggered activity in susceptible hearts.

History and naming: the structure is named after Jan Evangelista Purkinje, who described these fibers in the 19th century as a key part of cardiac conduction.