- Atrioventricular block
- Bradycardic arrhythmia
In AV block, the electrical excitation of the sinus node is only delayed (1st degree AV block), only partially (2nd degree) or not at all (3rd degree) passed on to the chamber muscles by the AV node or subordinate structures. This means that the flow of electrical potentials is interrupted at a certain point from the AV node downwards.
1st degree AV block
In 1st degree AV block, any potential that arises in the sinus node (pulse pacemaker of the heart) is still passed on, but the transfer is slowed down. So there is actually no real blockage here, only a delay. Symptoms: First-degree AV block doesn’t cause symptoms.
It can only be recognized in the ECG. Diagnosis: With 1st degree AV block, an extension of the PQ time is visible in the ECG, the distance between the P wave and the Q wave is more than 0.20 sec. Therapy: No therapy is necessary.
Second-degree AV block
With 2nd degree AV block, individual potentials of the sinus node are not passed on. Here again, a distinction is made between two forms, which have different prognoses. – Wenckebach block (IIa block): Here the distances between the P wave and the Q wave become longer and longer until a transition fails.
- Mobitz-Block (IIb-Block): Here the distance between P-wave and Q-wave remains normal, but there is always a sudden failure of a QRS complex. So not every P-wave is followed by a QRS complex. To make things even more complicated, we further differentiate between a 2:1 block (only one of two sine potentials is forwarded) or a 3:1 block (two of three sine potentials are forwarded)
3rd degree AV block
With the 3rd degree AV block (total AV block) there is a total line interruption. The potentials of the sinus node are not passed on. They only lead to a contraction of the atrium.
The chambers contract in time with subordinate structures such as the AV node. This beat is significantly slower than the sinus rhythm. Atrial and ventricular actions are therefore no longer properly coordinated.
The ECG shows P-waves that occur at a normal frequency. However, they are not related to the QRS complexes occurring at a slower frequency. It usually takes some time until the AV node or subordinate structures “jump on” and generate a replacement clock, this is called pre-automatic pause.
Symptoms AV block
The symptoms of the 2nd and 3rd degree AV block arise from the reduced heart rate and the resulting reduced pumping power. Due to the delayed or completely blocked potentials, the heart beats more slowly. The blood is transported less quickly in the organism.
The reduced pumping capacity is mainly manifested by symptoms such as dizziness or syncope (fainting fits), also known as Adams-Stokes fits. Adams-Stokes seizures are characterized by acute dizziness followed by brief unconsciousness caused by a reduction in the blood supply to the brain. In most cases, the symptoms do not occur under stress but at rest, because under stress the heart beats faster and the ability to conduct blood is improved.
In this way the actual disturbance can be absorbed. There are two additional dangers with total AV block:
- If the heart rate slows down considerably (less than 40 beats per minute), heart weakness (heart failure) develops. – During the pre-automatic pause, the chambers do not beat. Depending on the duration of the pause, this can lead to loss of consciousness, seizures (often misinterpreted as epilepsy), respiratory arrest and, if the pause lasts longer than three minutes, irreversible brain damage.