The heart pumps blood into the circulation with regular beats to supply the body and all of its organs with oxygen (task of the heart). It does this all by itself, i.e. it is not stimulated by nerves from the outside, but has specialized cells that function as an internal clock. This system of cells is known as a stimulation conduction system or pacemaker system.
The primary pacemaker/pacemaker is the so-called sinus node, which is located on the right atrium and normally ensures a heart rate of 60 to 80 beats per minute. It transmits the excitation so that the atria and then the ventricles contract one after the other to enable the heart to beat in a regulated rhythm. If, in the context of certain heart diseases, the heart does not beat fast enough or takes breaks, this conduction system must be supported by an external pacemaker.
First of all, it is important to decide whether the patient needs the pacemaker only for a limited time or whether it is needed permanently. Only in the second case will the pacemaker actually be implanted. Indications for a temporary treatment are, for example, cardiogenic shock (in which the heart cannot pump enough blood for a short time) or certain poisonings (for example with the plant foxglove).
The indication for long-term use of the pacemaker is mainly in bradycardia (when the heart beats too slowly), which causes the patient discomfort. Atrial fibrillation can also cause such a symptom, as the atrium contracts disorderly too quickly and too often, with only a few beats being able to be transmitted to the ventricles. The other large group of diseases for which there are indications for a pacemaker concerns the conduction system itself.
Here, on the one hand, there is a sinus node dysfunction (also known as sick sinus syndrome), in which the pacemaker function of the sinus node is disturbed or completely blocked, which means that the heartbeat can slow down to up to 40 beats per minute. The pacemaker must then practically take over the function of the sinus node. In addition, there are several types of so-called heart blocks, in which it is not the generation but the transmission of electrical impulses that is defective.
This conduction disturbance can be located inside the atrium, between the atrium and the ventricle, or inside the ventricle itself, whereby the conduction can either be delayed or fail completely. In this case, the pacemaker stimulates, depending on the type, either only the atrium or the atrium and ventricle. The carotid sinus syndrome is also an indication for a pacemaker.
In this disease, an area of the carotid artery is excessively sensitive. If this area is irritated (for example by jerky head movements), the heart rate drops extremely; the pacemaker must therefore stimulate the ventricles. Pacemakers are also indicated for cardiac arrhythmia, cardiac insufficiency (when the heart cannot pump enough blood to supply the body with adequate oxygen) and an insufficient pulse rate increase in stressful situations.
