Sinus node defect
If the sinus node fails as the primary pacemaker and stimulation center of the heart, a secondary pacemaker must step in for it (sick sinus syndrome). This is called the atrioventricular node (AV node) and can take over the function of the sinus node to a certain extent. It generates a rhythm with a lower frequency, so the heart does not beat as usual 60-70 times per minute, but only about 40 times. In certain diseases (e.g. coronary heart disease), the sinus node remains functional, but generates the excitations at a greater distance, so that the heart rate becomes slower (so-called sinus bradycardia).
Sick- Sinus- Syndrome
The term sick sinus syndrome summarizes several cardiac arrhythmias resulting from a defective sinus node. Men and women over the age of 50 are affected about equally frequently. The cause is often a scarred change in the tissue in the heart, where the specialized excitatory cells of the sinus node are located.
The first of these is high blood pressure (arterial hypertension), which leads to a pressure load on the atria and thus to overstretching and damage to the tissue in the area of the sinus node. Myocarditis (inflammation of the heart muscle) or coronary heart disease can also be the cause. Other heart diseases such as valvular heart disease can also be a trigger.Likewise, an overdose of certain drugs such as beta blockers can cause sick sinus syndrome.
Children who have to undergo surgery due to a congenital heart defect can also develop sick sinus syndrome as a result. There is no general consensus on the exact definition of the term sick sinus syndrome. Clinically, the term refers to a rhythm disturbance that occurs together with pronounced low and high pulse rates (tachycardia–bradycardia syndrome).
Sinus bradycardias without any other identifiable cause or a sinuatrial block are also summarized under the term. Symptomatically, bradycardia (too slow a heartbeat) manifests itself as dizziness, syncope (fainting) or hearing and vision impairment, whereas tachycardia (too fast a heartbeat) manifests itself as palpitations, chest tightness (angina pectoris) or shortness of breath (dyspnoea). The most important diagnostic tool is a long-term ECG and exercise ECG, which can be used to demonstrate the electrical activity of the heart.
Depending on the exact clinical picture, the therapy can be carried out with medication (with so-called antiarrhythmic drugs, drugs against cardiac arrhythmia) or a pacemaker must be used to replace the function of the defective sinus node. In Germany almost every third pacemaker is used in a patient with sick sinus syndrome.
