Sinoatrial block

The SA block ( sinoatrial block ) is a heart rhythm disorder. It is caused by delay or even interruption of the conduction of excitation from the sinus node to the atrial muscle (see heart, there rooms and vessels).

SA blocks are completely harmless and quite common especially in healthy heart usually. Rarely, however, they can cause serious symptoms such as sudden loss of consciousness ( syncope) or poor performance and then require specific therapy.

Causes

A sino-atrial block can have many causes, which can be found either on the heart itself or the autonomic nervous system. Also, endocrinological and psychological causes come into consideration. They range from harmless vagotonic states, as observed especially in young competitive athletes at rest, to cardiac arrest of several seconds duration at then usually already damaged heart. Also medications such as beta blockers can trigger an SA block.

Shapes and diagnostics

A distinction is made between three different types or degrees of SA block (similar to the nomenclature for AV block), with only the SA block second degree ( SA block II ° ) are diagnosed more or less reliable in the normal electrocardiogram ( ECG) can. The remaining species of the SA block can be detected only by special complex cardiac catheterizations.

SA block I °

The SA- block I ° is defined as the propagation delay from the sinus node to the atrium, but each impulse of the sinus node being passed over. He can not be seen on the surface ECG.

SA block II ° Type 1

When SA block II ° Type 1 ( Wenckebach or Mobitz type or 1- type ), the conduction disturbance in a steady extension of the line until now and then a heartbeat fails completely. In the ECG ( for nomenclature see ECG, there nomenclature and standard values ​​), it is often at increasingly shorter intervals between P waves and then a complete lack of cardiac activity ( P wave and QRS complex ) recognizable, with the distance to the next P- shaft is shorter than two preceding PP intervals.

SA block II ° Type 2

The SA block II ° Type 2 (or Mobitz type 2 ) is very similar to Type 1, also include both individual cardiac actions completely. However, in the ECG, the distance between the P-waves in the ideal case is equal to and failure of the heart action exactly twice as large (or larger by a multiple) as two previous PP- intervals.

SA block III °

In the third degree ( or complete ) sinoatrial block no impulse of the sinus node is more reconciled. In the healthy heart of the next -ranking physiological pacemaker ( AV) node assumes the impulse formation with 40 to 50 pulses per minute. In this way, only a so-called AV nodal rhythm in the ECG is usually seen, which brings to mind among many other causes also a SA block. In pre-damaged heart of the escape rhythm may be missing, which may under certain circumstances have a longer cardiac arrest with immediate unconsciousness result.

Therapy

Few patients with an SA block require any therapy. In most cases, this is only the case if the block causes symptoms such as syncope or heart failure.

In an emergency occurs, intravenous drug therapy with atropine and epinephrine, if necessary. In all other cases it is first checked whether or not the SA block is caused by drugs or a disturbance of the electrolyte concentration in the blood. If you can not clear symptoms of SA block removed by the discontinuation of medication or the compensation of electrolyte disturbances, there is an indication for pacemaker supply. When SA block pure case a stimulating exclusively in the court of one -chamber system is given preference. In very rare cases, such as when a pacemaker operation is not reasonable, even a medical term therapy can be attempted with ipratropium bromide.