Sinoatrial block (SA block): ECG criteria, causes and clinical features

Sinoatrial block (SA block): ECG criteria, causes and clinical features

Sinoatrial block (SA block): from ECG to clinical management Sinoatrial (SA) block implies that the impulses discharged in the sinoatrial node are either not conducted to the atria or are so with a delay. This manifests with loss of P-waves (loss of atrial activation) and consequently loss of QRS complexes (loss of ventricular depolarization). Sinoatrial block is subdivided into three degrees according to the nature of the block. The nature of these blocks is very similar to the  atrioventricular (AV) blocks . Importantly, first-degree sinoatrial block and third-degree sinoatrial block cannot be diagnosed using surface  ECG  (i.e ECG recorded on the body surface). This is because the electrical potentials generated by the sinoatrial node are much too small to be detected on the surface ECG. Intracardiac  electrodes  – with placement of electrodes against the sinoatrial node – are necessary to diagnose first- and third-degree sinoatrial block. However, second-degree sinoatrial block may be dia…

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