What is the conduction system?
The conduction system consists of various specialized heart muscle cells that transmit electrical impulses, causing the heart muscle to contract rhythmically.
Pacemaker generates electrical impulses
The electrical impulses are generated by so-called pacemaker cells. They are mainly located in two structures: sinus node (the primary pacemaker of the heart) and AV node (secondary pacemaker). They are both located in the right atrium and together constitute the excitation generation system.
Normally, the sinus node generates the electrical impulses, which then propagate through the atria to the AV node as the atria contract. This is located at the border of the ventricle. From here, excitation passes through the conduction system to the ventricles, which then contract.
Like the sinus node, the AV node is capable of spontaneous, automatic impulse formation. However, this only comes into play if the sinus node fails as the primary pacemaker, because the natural frequency of the AV node, at 40 to 50 impulses per minute, is significantly lower than that of the sinus node, at around 70 impulses per minute.
Conduction system: transmission of impulses
The His bundle passes from the AV node through the valvular plane to the septum between the two main chambers (ventricular septum). There it splits into two branches called the tawara (ventricular) legs. The right leg pulls toward the apex of the heart on the right side of the ventricular septum, and the left leg pulls toward the left side of the septum. Both tawara legs branch from here to form the Purkinje fibers. These run within the working muscles of the heart and ultimately transmit electrical impulses to the individual muscle cells of the ventricles, causing them to contract. This forces blood from the left ventricle into the aorta and from the right ventricle into the pulmonary artery.
Influence of the nervous system
The conduction system is influenced by the autonomic nervous system (sympathetic and parasympathetic). Stimulation of the sympathetic nervous system increases heart rate and cardiac output, while stimulation of the parasympathetic nervous system decreases heart rate via a decrease in pacing rate in the sinus node.
What problems can occur in the conduction system?
The conduction system may also be disrupted in the tawara (ventricular) thighs, which is called intraventricular block (thigh block).
