Editing Heart block (section)

===SA nodal blocks===
SA blocks rarely give severe symptoms, because even if an individual had complete block at this level of the conduction system (which is uncommon), the secondary pacemaker of the heart would be at the AV node, which would fire at 40 to 60 beats a minute, which is enough to retain [[consciousness]] in the resting state. However, SA block is capable of causing problematic symptoms even so, and may also hint at conduction issues elsewhere in the heart, and therefore SA blocks are – despite their lower level of life-threatening risk – still "the most common indication for pacemaker implantation in the US".<ref>[https://books.google.com/books?id=h90AyFfNahsC&dq=first+degree+infra+hisian+heart+block&pg=PA144 ''Electrophysiology: A Companion Guide'', Steinberg (ed.)], p. 142</ref>

Types of SA nodal blocks include:
* SA node Wenckebach (Mobitz I)<ref name="Fuster-2000">{{cite book | author=Valentin Fuster | author2=R. Wayne Alexander | author3=Robert A. O'Rourke | author4=Robert Roberts | title=Hurst's The Heart | edition=10th | publisher=McGraw-Hill Professional Publishing | date=November 2000 | pages=Figure 24–60b | isbn= 978-0-07-135695-4 | no-pp=true|display-authors=etal}}</ref>
* SA node Mobitz II
* SA node exit block

In addition to the above blocks, the SA node can be suppressed by any other arrhythmia that reaches it.  This includes retrograde conduction from the ventricles, [[Cardiac ectopy|ectopic]] atrial beats, [[atrial fibrillation]], and [[atrial flutter]].{{cn|date=February 2021}}

The difference between SA node block and SA node suppression is that in SA node block an electrical impulse is generated by the SA node that doesn't make the atria contract.  In SA node suppression, on the other hand, the SA node doesn't generate an electrical impulse because it is reset by the electrical impulse that enters the SA node.{{cn|date=February 2021}}