SA block
| Classification according to ICD-10 | |
|---|---|
| I45.5 | Other specified heart block - sinoatrial block |
| ICD-10 online (WHO version 2019) | |
The SA block ( sinus atrial block ) is a cardiac arrhythmia . It arises from a delay or even interruption of the conduction of excitation from the sinus node to the atrial muscles (see heart , there spaces and vessels ).
SA blockages are quite common and mostly completely harmless, especially in people with healthy hearts. Rarely, however, can they cause serious symptoms such as sudden loss of consciousness ( syncope ) or poor performance and then require targeted therapy .
causes
A sinus atrial block can have a variety of causes, which can be found either in the heart itself or in the autonomic nervous system . Also, endocrinological and psychological causes can be considered. The spectrum ranges from harmless vagotonic states, such as those observed in young competitive athletes in particular when they are resting, to cardiac arrests lasting several seconds when the heart is usually damaged. Also drugs such as beta blockers can trigger an SA block.
Forms and diagnostics
A basic distinction is made between three different types or degrees of severity of SA block (similar to the nomenclature for AV block ), with only the second-degree SA block ( SA block II ° ) being diagnosed more or less reliably in the normal electrocardiogram (ECG) can. The other types of SA block can only be detected by means of special, complex cardiac catheter examinations .
SA block I °
The SA block I ° is defined as the line delay from the sinus node to the atrium, but each pulse of the sinus node is transferred. It cannot be seen in the surface ECG.
SA block II ° type 1
With SA-Block II ° Type 1 (or Wenckebach-Type or Mobitz-1-Type ) the conduction disturbance leads to a steady lengthening of the conduction, until every now and then a heartbeat fails completely. In the ECG , it can often be recognized by increasingly shorter intervals between the P waves and then a complete lack of cardiac action (P wave and QRS complex), whereby the distance to the next P wave is shorter than two previous PP intervals.
SA block II ° type 2
The SA block II ° type 2 (or Mobitz-2 type ) is very similar to type 1, here too, individual heart actions are completely canceled. However, in the ECG, the distance between the P waves is ideally the same and, if the cardiac action fails, it is exactly twice as large (or several times larger) than the two preceding PP distances.
SA block III °
In the third-degree (or complete) sino-atrial block, no impulse from the sinus node is passed over. In a healthy heart, the next-ranking physiological pacemaker ( AV node ) takes over the generation of excitation with 40 to 50 pulses per minute. In this way, only a so-called AV node rhythm can usually be recognized in the ECG, which, along with many other causes, also suggests an SA block. If the heart is damaged, the substitute rhythm may be missing, which in certain circumstances can lead to a prolonged cardiac arrest with immediate loss of consciousness .
therapy
Only a few patients with an SA block require therapy at all. As a rule, this is only the case if the block causes symptoms such as syncope or cardiac insufficiency .
In an emergency, intravenous drug therapy with atropine and possibly adrenaline is carried out . In all other cases, the first step is to check whether the SA block is caused by medication or a disturbance in the electrolyte concentration in the blood. If clear symptoms of the SA block cannot be eliminated by discontinuing medication or compensating for electrolyte imbalances, there is an indication for pacemaker care . With the pure SA block, preference is given to a 1-chamber system that stimulates exclusively in the atrium. In very rare cases, for example when a pacemaker operation is unreasonable, long-term drug therapy with ipratropium bromide can be tried.
