Overview
Sinoatrial exit block is a delay in conduction between the sinoatrial node and atrial myocardium.
Pathogenesis
Causes of Sinoatrial Exit Block
- Idiopathic degeneration
- Myocardial infarction
- Infiltrative disease - sarcoidosis, amyloidosis, haemochromatosis
- Connective tissue disease - SLE, scleroderma, RA
- Cardiac surgery - valvular surgery, correction of congenital heart disease
- Infections - Lyme disease, endocarditis
Diagnosis
ECG Findings
- First degree - not detectable on ECG
- 2nd Degree: type I (Wenckebach) - progressively shortened PP intervals, followed by a pause
- 2nd degree: type II - constant PP interval, with a pause that is a multiple of the PP interval.
- 3rd degree - complete failure of transmission to the atria; indistinguishable from sinus arrest on ECG
Examples
- 2nd degree SA exit block: type I
![2nd degree SA exit block type I]()
- 2nd degree SA exit block: type II
![2nd degree SA exit block type II]()
- 3rd degree SA exit block
![3rd degree SA exit block]()
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