Pathogenesis (development of disease)
Sinuatrial block is a block in the conduction of excitation in the atrium due to a disturbance between the sinoatrial node and the atrium.
Three degrees of severity of sinuatrial block can be distinguished:
- 1st-degree SA block – conduction delay of excitation from the sinoatrial node to the atrial muscles; not detectable on electrocardiogram (ECG).
- SA block 2nd degree – intermittent conduction interruption (not every excitation is transmitted).
- Type 1 (Wenckebach periodicity): steady prolongation of conduction until a heartbeat now and then fails completely.
- Type 2 (Mobitz): Individual heartbeats also fail completely here. In the ECG heart pauses are recognizable.
- SA block 3rd degree – Total conduction interruption, impulse transmission to the atrial myocardium is absent; In a healthy heart, the AV node (electrical connection between atria and ventricles) then takes over the excitation formation with 40-50 impulses/minute (replacement rhythm). In the ECG, a so-called AV-node rhythm is recognizable. If the heart is pre-damaged, the replacement rhythm of the AV node may be missing, which may lead to prolonged cardiac arrest with immediate unconsciousness.
Etiology (Causes)
Causes related to disease
- Coronary artery disease – atherosclerosis (arteriosclerosis, hardening of the arteries) of the coronary arteries.
- Myocardial infarction (heart attack)
- Myocarditis (inflammation of the heart muscle)
- Sick sinus syndrome – disturbances in cardiac conduction due to damage to the sinus node.
Medication
- Overdose of antiarrhythmic drugs – drugs for cardiac arrhythmias such as ajmaline or lidocaine.
- Overdose of digitalis glycosides – medications such as digoxin that are prescribed to strengthen the heart in heart failure (cardiac insufficiency) and in cardiac arrhythmias
