Purkinje Fibers - Function

Function

Heart rate is governed by many influences from the Autonomic Nervous System. The Purkinje Fibers do not have any known role in setting heart rate, but are influenced by Sympathetic discharge from the Sinoatrial node and thoracic Spinal Accessory Ganglia.

During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from both the left and right bundle branch to the myocardium of the ventricles. This causes the muscle tissue of the ventricles to contract, thus enabling a force to eject blood out of the heart; either to the Pulmonary circulation from the right ventricle or to the Systemic circulation from the left ventricle.

Atrial and ventricular discharge through the Purkinje trees is assigned on a standard Electrocardiogram as the P Wave and QRS complex, respectively.

Purkinje fibers also have the ability of automaticity, firing at a rate of 15-40 beats per minute if left to their own devices. In contrast, the SA node outside of parasympathetic control can fire a rate of almost 100 beats per minute. - in short, they generate action potentials, but at a slower rate than sinoatrial node and other atrial ectopic pacemakers. Thus they serve as the last resort when other pacemakers fail. When a pukinje fiber does fire, it is called a premature ventricular contraction or PVC. Another name given is ventricular escape. It plays a vital role in the circulatory system.