Editing Heart block (section)

==Types==
[[File:ConductionsystemoftheheartwithouttheHeart-en.svg|thumb|280px|Conduction system of the heart]]
[[File:Type I A-V block 5-to-4 Wenckebach periods.png|thumb|[[Sinus rhythm]] with acute inferior [[infarction]] complicated by Type I [[Second-degree atrioventricular block|AV block]] manifest in the form of 5:4 [[Wenckebach]] periods; R-P/P-R reciprocity.]]
[[File:Sinus rhythm with 3-to-2 and 2-to-1 Type II A-V block.png|thumb|Sinus rhythm (rate = 100/min) with 3:2 and 2:1 Type II AV block; [[right bundle branch block]]]]
[[File:Complete A-V block with resulting junctional escape.png|thumb|[[Sinus tachycardia]] with complete AV block and resulting junctional escape]]
Following the path of the electrical signals, the places where conduction can be blocked give rise to different kinds of heart blocks:
{| class=wikitable
|-
! Location !! Name
|-
| Within the [[sinoatrial node]] (SA node or Sinus node), where the [[Cardiac pacemaker|heart's signals originate]] || [[Sinoatrial block|Sinoatrial nodal block]]s (often abbreviated "SA nodal block" or "SA block", sometimes written "Sinuatrial block")
|-
| Within the [[atrioventricular node]] (AV node) || [[Atrioventricular block]] (often abbreviated "AV nodal block", "AV block" or AVB).
|-
| At and below the [[bundle of His]] || [[Intra-Hisian block]]s and [[Infra-Hisian block]]s respectively.
|-
| Within the left or right [[bundle branch]]es || [[Bundle branch block]]s.
|-
| Within the fascicles of the left [[bundle branch]] || "Fascicular block" or hemiblocks.
|}
SA and AV node blocks are each divided into three degrees, with second degree blocks being divided into two types (written either "type I or II" or "type 1 or 2").  In an SA block, the electrical impulse is delayed or blocked on the way to the atria, thus delaying atrial depolarization. By contrast, an AV block occurs in the AV node and delays ventricular depolarization. The term "Wenckebach block" is also used for some heart blocks, and can refer to a second degree type I block in ''either the SA node or the AV node''; however, the ECG features of the two are quite distinctly different.

===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}}

===AV nodal blocks===
There are three basic types of [[Atrioventricular block|AV nodal block]]:
* [[First-degree atrioventricular block|First-degree AV block]]
* [[Second-degree atrioventricular block|Second-degree AV block]]
** Type 1 second-degree AV block (Mobitz I), also known as a Wenckebach block<ref name="Dorland's227">{{cite book |title=Dorland's Illustrated Medical Dictionary |date=2012 |publisher=Elsevier |isbn=978-1-4160-6257-8 |page=227 |edition=32nd}}</ref>
** Type 2 second-degree AV block (Mobitz II), also known as a Hay block – due to a block in or below the bundle of His<ref name="Dorland's227"/>
* [[Third-degree atrioventricular block|Third-degree AV block]] (complete heart block)

===Infra-Hisian block===
Infra-Hisian block is that of the distal conduction system.  Types of infra-Hisian block include:
* Type 2 second degree heart block (Mobitz II) – a type of AV block due to a block within or below the [[bundle of His]]<ref name="Dorland's227"/>
** [[Left anterior fascicular block]]
** [[Left posterior fascicular block]]
* [[Right bundle branch block]]
* [[Left bundle branch block]]

Of these types of infra-Hisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.{{cn|date=February 2021}}