What is "heart block"

n. (context pathology English) A disease in the electrical system of the heart, opposed to coronary artery disease, which is disease of the blood vessels of the heart.

n. recurrent sudden attacks of unconsciousness caused by impaired conduction of the impulse that regulates the heartbeat [syn: Adams-Stokes syndrome, Stokes-Adams syndrome, atrioventricular block]

Heart block is a disease or inherited condition that causes a fault within the heart's natural pacemaker due to some kind of obstruction (or "block") in the electrical conduction system of the heart. Despite the severe-sounding name, heart block may often cause no symptoms at all in some cases, or occasional missed heartbeats in other cases (which can cause lightheadedness, syncope (fainting), and palpitations), or may require an artificial pacemaker to be implanted, depending upon exactly where in the heart conduction is being impaired and how significantly it is affected.

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 heart beat in a living person; incorrect conduction 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 branches to the point of the apex of the fascicular branches (shown in the diagram on the right). 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 branches (" 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 " 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 " 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.