SA Blocks

Sinoatrial node blocks affect conduction through the SA node. The degree of the block can be first, second or third. A first degree block is not seen on the ECG, as conduction is just delayed. A second degree block causes intermittent failure of the impulse to exit the node and a third degree block causes all impulses to be blocked from exiting the node. A third degree block can only be diagnosed during electrophysiological studies.