Causes | AV block


An AV block is usually caused by pathological changes in the stimulus conduction system. CHD (coronary heart disease), a heart attack and medication can lead to an AV block. It usually occurs in older people.

Diagnosis of the AV block by ECG

The diagnosis is made on the basis of the medical history and the typical ECG (electrocardiogram) changes. In case of a relatively frequent and harmless AV block grade 1, the distance between the P- wave and the QRS complex is more than 200 ms. Treatment is not necessary and often it is a random finding in the ECG.

A distinction is made between a Mobitz type and a Wenckebach type for grade 2 AV block. With the Wenckebach type, the distance between the P wave and the QRS complex increases from beat to beat. When a certain distance is reached, a QRS complex is eliminated.

With the Mobitz type, the stimulus is transferred to the chamber only every 2 to 3 strokes, which leads to an irregular formation of a QRS complex. A grade 3 AV block is the most dangerous AV block and always requires treatment. Here, the excitation is sent so undirected over the heart muscle that the atria and ventricle beat in an uncoordinated manner.

The normal human pulse and, if necessary, blood pressure cannot be maintained in this way. The treatment should be carried out quickly, as the normal supply of blood to the body cannot be guaranteed with an untreated grade 3 AV block. The uncoordinated propagation of excitation becomes noticeable in the ECG by P waves and QRS complexes which do not appear at certain distances from each other.

So it can happen that you see a QRS jag first and then two P waves instead of one P wave followed by QRS complex after a certain time. AV block grade 3 is not only noticed symptomatically by the patient (loss of performance, tiredness, indisposition) but also manifests itself by a restless pulse. The danger of grade 3 AV block is syncope, i.e. temporary unconsciousness.


If the AV block was caused by medication or a disease (e.g. myocarditis), the treatment of this disease and discontinuation of medication is the main focus. The AV block can then recede. With 1st and 2nd degree Wenckebach type AV block, no further therapy is usually required. In 2nd degree type Mobitz AV block and total AV block, pacemaker therapy is indicated. Usually an atrial system (e.g. DDD) is implanted.


The AV block is also called atrioventricular arousal disorder. This disturbance of the transmission of excitation in the heart affects the atrioventricular node (AV node) or subsequent structures such as the HIS bundle, the two tawara legs or the Purkinje fibers. The excitation can only be passed on slowly or sometimes not at all through the AV block.

Usually the AV-block develops when the tissue shows degenerations, because the affected person is already older. In addition, certain medications and cardiovascular diseases such as heart attack are also possible causes. This disorder can be of varying degrees of severity.

Some patients do not notice anything at all, while in others the heartbeat slows down (bradycardia), but it can lead to cardiac arrest. There are 3 different degrees of the disorder, which have different degrees of severity:

  • In first-degree AV block, the excitation is delayed from the atrium to the ventricle. Clinically, first-degree AV block has no significance at all, since there is no drop in ventricular frequency and the patients have no complaints, nor is this disorder noticeable in any way outside the ECG.

However, the PR interval is more than 0.2 seconds longer. Even though this block has little clinical relevance, electrolytes can be given in isolated cases. – With AV block type 2 the AV node is not completely blocked.

This means that a few few excitations are not transmitted from the atrium to the chamber and thus the frequency falls below that of the sinus node. The PR interval here is longer than 0.45 seconds and you can see P waves but no QRS complexes. This interference can be divided into two different types.

There is the Mobitz Type 1 (Wenckebach-Block) where with each heartbeat the PQ interval gets longer until a transition is no longer present. And then it starts again. With this type, no treatment is usually necessary.

There is also Mobitz Type 2 in which the PQ interval always remains the same but very often the excitation is not passed on. The disturbance here is usually below the AV node. For this most patients need a pacemaker, otherwise the prognosis is poor.

  • The 3rd degree AV block is the last block in this disorder and also the most severe. Here the excitation transfer fails completely and the chamber is no longer excited. Sometimes, however, the chamber moves arrhythmically to the atria, since the AV node as well as the subsequent stations of the excitation transition can also develop pacemaker potentials like HIS bundles.

However, these frequencies are significantly below those of the sinus node. As therapy, a pacemaker is implanted here. In general, cardiovascular disorders can be detected very well by the ECG. Even if the patients have no complaints, the ECG looks characteristic.