Editing Heart block (section)

{{short description|Disorder of heart rhythm}}
{{distinguish|cardiac arrest|heart failure|myocardial infarction}}
{{see also|Congenital heart block}}
'''Heart block''' ('''HB''')<ref>{{Cite book|title=Logan's Medical and Scientific Abbreviations|last1=Logan|first1=Carolynn M.|last2=Rice|first2=M. Katherine|publisher=J. B. Lippincott and Company|year=1987|isbn=0-397-54589-4<!--hardbound copy-->|pages=232}}</ref> is a disorder in the [[heart]]'s rhythm due to a fault in the [[cardiac pacemaker|natural pacemaker]].<ref name="Heart">{{cite web |title= Conduction Disorders |url= https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/conduction-disorders |website= sitecoreprod.heart.org{{!}}beta.heart.org{{!}}www.heart.org{{!}}heart.org{{!}}*.azurewebsites.net{{!}}localhost |language= en}}</ref> This is caused by an obstruction – a block – in the [[electrical conduction system of the heart]]. Sometimes a disorder can be [[genetic disorder|inherited]]. Despite the severe-sounding name, heart block may cause no symptoms at all in some cases, or occasional missed heartbeats in other cases (which can cause light-headedness, [[Syncope (medicine)|syncope]] (fainting), and [[palpitation]]s), or may require the implantation of an  [[Artificial cardiac pacemaker|artificial pacemaker]], depending upon exactly where in the heart conduction is being impaired and how significantly it is affected.

Heart block should not be confused with other conditions, which may or may not be co-occurring, relating to the heart and/or other nearby organs that are or can be serious, including [[angina]] (heart-related chest pain), heart attack ([[myocardial infarction]]), any type of [[heart failure]], [[cardiogenic shock]] or other types of shock, different types of abnormal heart rhythms ([[arrhythmias]]), [[cardiac arrest]], or [[respiratory arrest]].

In severe cases where the heart's ability to control and trigger heartbeats may be completely ineffective or unreliable, heart block can usually be treated by inserting an artificial pacemaker, a medical device that provides correct electrical impulses to trigger heart beats, compensating for the natural pacemaker's unreliability. Therefore, heart block frequently has no effects, or mild and occasional effects, and is not life-threatening in the vast majority of cases, and is usually treatable in more serious cases.

The human [[heart]] uses electrical signals to maintain and initiate the regular  [[Cardiac cycle|heartbeat]] in a living person; incorrect conduction or interference from external sources can lead to mild or serious symptoms depending upon the location of the blockage and how severely conduction is being blocked. Conduction is initiated by the [[sinoatrial node]] ("sinus node" or "SA node"), and then travels to the [[atrioventricular node]] ("AV node") which also contains a secondary "pacemaker" that acts as a backup for the SA nodes, then to the [[bundle of His]] and then via the [[bundle branch]]es to the point of the apex of the  [[muscle fascicle|fascicular branches]]. Blockages are therefore classified based on where the blockage occurs – namely the SA node ("[[Sinoatrial block]]"), [[AV node]] ("[[AV block]]" or '''AVB'''), and at or below the [[bundle of His]] ("Intra-Hisian" or "Infra-Hisian block" respectively). Infra-Hisian blocks may occur at the left or right [[bundle branch]]es ("[[bundle branch block]]") or the fascicles of the left bundle branch ("fascicular block" or "[[Hemiblock]]"). 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"). The term "[[Karel Frederik Wenckebach|Wenckebach]] block" is also used for second degree type 1 blocks of either the SA or AV node; in addition second-degree blocks type 1 and 2 are also sometimes known as " [[Woldemar Mobitz|Mobitz]] 1" and "Mobitz 2".

Clinically speaking, the blocks tend to have more serious potential the closer they are to the "end" of the electrical path (the muscles of the heart regulated by the heartbeat), and less serious effects the closer they are to the "start" (at the SA node), because the potential disruption becomes greater as more of the "path" is "blocked" from its "end" point.  Therefore, most of the important heart blocks are AV nodal blocks and infra-Hisian blocks. SA blocks are usually of lesser clinical significance, since in the event of SA block, the AV node contains a secondary pacemaker which would still maintain a heart rate of around 40–60 beats per minute, sufficient for [[consciousness]] and much of [[daily life]] in the majority of individuals.