Internal Medicine

AV block

Synonyms in the broadest sense

Atrioventricular block
bradycardiac arrhythmia

definition

With AV block, the electrical excitation of the Sinus node from the AV node or subordinate structures only delayed (AV block 1st degree), only partially (2 degrees) or not (3 degrees) forwarded to the ventricular muscles. This means that the flow of electrical potentials is interrupted at a certain point from the AV node downwards.

1st degree AV block

At the 1st degree AV block every potential in the sinus node (pulse pacemaker of the Heart) arises, still forwarded Indeed the transition is slowed down. So there is actually no real blockage here, just a delay.

Symptoms: The 1st degree AV block does not cause symptoms. You can recognize him alone in the EKG.
Diagnosis: In the case of AV block of the 1st degree, an extension of the PQ time can be seen in the ECG, the distance between the P wave and the Q spike is over 0.20 seconds.
therapy: No therapy is required.

2nd degree AV block

At the 2nd degree AV block individual potentials of the sinus node are not passed on. A distinction is made here between two forms that 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 the P wave and the Q wave remains normal, but a sudden failure of a QRS complex occurs again and again. So there is not a QRS complex following every P wave. To make it even more complicated, a further distinction is made here between a 2: 1 block (only one of two sine potentials is passed on) or a 3: 1 block (two of 3 sine potentials are passed on)

3rd degree AV block

At 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 the contraction of the atrium. The chambers contract in time with subordinate structures such as of the AV node. This cycle is significantly slower than the sinus rhythm. Atrial actions and chamber actions are no longer properly coordinated. in the EKG one sees P-waves that occur with a normal frequency. However, they are not related to the QRS complexes that occur with a slower frequency. It usually takes a certain amount of time until the AV node or subordinate structures "start" and generate a replacement clock, this is called pre-automatic pause.

Symptoms of AV block

The symptoms of 2nd and 3rd degree AV block arise from the depressed Heart rate and the consequent reduced pumping capacity. This beats through the delayed or completely blocked potentials heart slower. The blood is transported less quickly in the organism. The reduced pumping performance manifests itself primarily through symptoms such as dizziness or syncope (fainting spells), too Adams-Stokes attacks called. Adam Stokes seizures are characterized by an acute feeling of dizziness with subsequent, brief loss of consciousness, which is caused by the reduced blood supply to the brain. Most of the time, the symptoms do not occur under exertion, but rather at rest, since under exertion the heart beats faster and conductivity 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 sharply (less than 40 beats per minute), heart failure develops (Heart failure).
The chambers do not beat during the pre-automatic pause. Depending on the length of the break, it can lead to loss of consciousness, seizures (often misinterpreted as epilepsy), respiratory failure and irreversible brain damage if there is a break of more than three minutes.

causes

An AV block is usually caused by pathological changes in the conduction system. The KHK (Coronary heart disease), a Heart attack and medication can lead to AV block. Mostly it occurs in older people.

Diagnosis of the AV block by ECG

The diagnosis is based on the anamnesis and the typical ECG (Electrocardiogram) Changes made.

For information on the process and interpretation of an ECG, also read: EKG or AV block due to myocardial inflammation in the EKG

ECG changes in AV block grade 1

With 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 Incidental finding in the EKG.

EKG changes in AV block grade 2

A distinction is made between a Mobitz type and a Wenckebach type in AV block grade 2. In 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 disappears. With the Mobitz type, the stimulus is only transmitted to the chamber every 2 to 3 beats, which leads to a irregular formation of a QRS complex leads.

EKG changes in AV block grade 3

A grade 3 AV block represents the most dangerous and always in need of treatment AV block represent.Here the excitation is sent so undirected via the heart muscle that the atria and ventricle beat in an uncoordinated manner. The normal human pulse and possibly also blood pressure cannot be maintained in this way. Treatment should be carried out quickly, since with an untreated Grade 3 AV block, the normal supply of blood to the body cannot be guaranteed. The uncoordinated spread of excitation makes itself felt in the EKG P waves and QRS complexes noticeable, which do not appear at certain distances from one another. So it can happen that you first see a QRS spike and then two P waves instead of one P wave followed by QRS complex after a certain time.
Grade 3 AV block is not only noticed symptomatically by the patient (loss of performance, tiredness, malaise), but is also noticeable through a restless pulse. The danger of AV block grade 3 is syncope, i.e. temporary loss of consciousness.

therapy

Was the AV block caused by medication or a disease (e.g. a Myocarditis), the focus is on treating this disease and stopping medication. The AV block can then recede.

In most cases, no further therapy is required for the 1st and 2nd degree Wenckebach AV block.

With 2nd degree AV block type Mobitz and a total AV block there is one Pacemaker therapy indexed. Usually an atrial involved system (e.g. DDD) is implanted.

Summary

Of the AV block is also called atrioventricular arousal disorder.
This disturbance of the conduction of excitation in the heart affects the Atrioventricular node (AV node) or subsequent structures like that HIS bundle, the two Tawara thigh or the Purkinje fibers.

The excitation can only be passed on slowly or sometimes not at all through the AV block. The AV block usually develops when the tissue shows degeneration because the affected person is older.
Also, certain medications as well as cardiovascular diseases are also like Heart attack a possible reason. This disorder can vary in severity.
Some patients do not notice anything, while others have a slower heartbeat (Bradycardia), but it can go up to one Cardiac arrest to lead.

There are 3 different degrees of disorder, which have different degrees of severity:

With 1st degree AV block the excitement is delayed from Forecourt directed to the ventricle. Clinically, the first-degree AV block has no meaning at all, there no trash the ventricular frequency takes place and the patients neither have symptoms nor is this disturbance noticeable in any way outside of the ECG.
The PR interval is longer than 0.2 seconds. Even if this block is of 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 excitations are not transferred from the atrium to the ventricle and so 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 from time to time but no QRS complexes. This disorder can be divided into two different types.
There is Mobitz type 1 (Wenckebach block) in which the PQ interval becomes longer with each heartbeat, until a transition no longer takes place. And then it starts all over again. Treatment of this type is usually not necessary.
Then there is also that Mobitz type 2 in which the PQ interval always remains the same but very often an excitation is not passed on. The disorder here is mostly below the AV node. Most patients need a pacemaker for this, otherwise the prognosis is poor.
The 3rd degree AV block is the last block in this disorder and also the most serious. Here the conduction of excitation fails completely and the chamber is no longer excited.
Sometimes the ventricle also moves arrhythmically to the atria, since the AV node and the subsequent stations of the conduction of excitation such as HIS bundles can develop pacemaker potentials. However, these frequencies are well below those of the sinus node. A pacemaker is implanted here as therapy. In general, cardiovascular disorders can be recognized very well through the EKG. Even if the patient has no symptoms, the EKG looks characteristic.