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Heart block ( HB) (1987). 9780397545896, J. B. Lippincott and Company. ISBN 9780397545896 is a disorder in the heart's rhythm due to a fault in the natural pacemaker. This is caused by an obstruction – a block – in the electrical conduction system of the heart. Sometimes a disorder can be genetic disorder. Despite the severe-sounding name, heart block may cause no symptoms at all or mere occasional missed Cardiac cycle and ensuing light-headedness, syncope (fainting), and . However, depending upon exactly where in the heart conduction is impaired and how significantly, the disorder may require the implantation of an artificial pacemaker, a medical device that provides correct electrical impulses to trigger heartbeats, compensating for the natural pacemaker's unreliability, so making heart block usually treatable in more serious cases.
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 heart failure, cardiogenic shock or other types of shock, different types of abnormal heart rhythms (arrhythmias), cardiac arrest, or respiratory arrest.
The human heart uses electrical signals to maintain and initiate the regular heartbeat in a living person. 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 to the point of the apex of the muscle fascicle. 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 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 " Woldemar 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 an SA node 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 most cases.
| Sinoatrial block (often abbreviated "SA nodal block" or "SA block", sometimes written "Sinuatrial block") |
| Atrioventricular block (often abbreviated "AV nodal block", "AV block" or AVB). |
| Intra-Hisian blocks and Infra-Hisian blocks respectively. |
| Bundle branch blocks. |
| "Fascicular block" or hemiblocks. |
Types of SA nodal blocks include:
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 atrial beats, atrial fibrillation, and atrial flutter.
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 does not make the atria contract. In SA node suppression, on the other hand, the SA node does not generate an electrical impulse because it is reset by the electrical impulse that enters the SA node.
Of these types of infra-Hisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.
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