In some people, they can cause fainting, altered mental status, chest pain, hypoperfusion, and signs of shock.

In a first degree sinoatrial block, there is a lag between the time that the SA node fires and actual depolarization of the atria.

This rhythm is not easily detectable using state of the art (the highest level of scientific development at the current state in time) diagnostic equipment, thus is currently not recognizable on an ECG strip because an ECG strip does not denote when the SA node fires.

It can be detected only during an electrophysiology study when a small wire is placed against the SA node from within the heart and the electrical impulses can be recorded as they leave the p-cells in the centre of the node [ see pacemaker potential ], followed by observing a delay in the onset of the p wave on the ECG.

Note that this is quite different from the Wenckebach AV block, in which the PR interval gets progressively longer, before the dropped QRS segment.

A second degree type II, or sinus exit block, is a regular rhythm that may be normal or slow.