P1-58 LATE RECOVERY OF TRANSIENT COMPLETE HEART BLOCK SECONDARY TO RHEUMATIC CARDITIS: A CASE FOR WATCHFUL WAITING RATHER THAN PERMANENT PACING. AMA Credit Designation Statement - Physicians The American Heart Association designates this live activity for a maximum of 2.00 AMA PRA Category 1 Creditsâ¢. Physicians should claim only the credit commensurate with the extent of their participation in the activity. AMA Credit Designation Statement - Physicians The American Heart Association designates this live activity for a maximum of 2.00 AMA PRA Category 1 Creditsâ¢. Physicians should claim only the credit commensurate with the extent of their participation in the activity.
Heart block | |
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ECG showing types of heart block | |
Specialty | Cardiology |
Heart block (HB)[1] is a disorder in the heart's rhythm due to a fault in the natural pacemaker.[2] This is caused by an obstruction â a block â in the electrical conduction system of the heart. Sometimes a disorder can be 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 (fainting), and palpitations), or may require the implantation of an 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 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 branches to the point of the apex of the 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 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.
Types[edit]
Conduction system of the heart
Sinus rhythm with acute inferior infarction complicated by Type I AV block manifest in the form of 5:4 Wenckebach periods; R-P/P-R reciprocity.
Sinus rhythm (rate = 100/min) with 3:2 and 2:1 Type II AV block; right bundle branch block
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:
![Heart Heart](https://litfl.com/wp-content/uploads/2018/08/3rd-degree-heart-block.jpg)
Location | Name |
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Within the sinoatrial node (SA node or Sinus node), where the heart's signals originate | Sinoatrial nodal blocks (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 blocks and Infra-Hisian blocks respectively. |
Within the left or right bundle branches | Bundle branch blocks. |
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[edit]
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'.[3]
Types of SA nodal blocks include:
- SA node Wenckebach (Mobitz I)[4]
- 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, ectopic atrial beats, atrial fibrillation, and atrial flutter.[citation needed]
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.[citation needed]
AV nodal blocks[edit]
There are three basic types of AV nodal block:
- Second-degree AV block
- Type I second-degree AV block (Mobitz I), also known as a Wenckebach block[5]
- Type 2 second-degree AV block (Mobitz II) - due to a block in or below the bundle of His[5]
- Third-degree AV block (complete heart block)
Infra-Hisian block[edit]
Infra-Hisian block is that of the distal conduction system. Types of infra-Hisian block include:
- Type 2 second degree heart block (Mobitz II) âa type of AV block due to a block within or below the bundle of His[5]
Complete Heart 1 1 Scale Model Kit
Of these types of infra-Hisian block, Mobitz II heart block is considered most important because of the possible progression to complete heart block.[citation needed]
References[edit]
- ^Logan, Carolynn M.; Rice, M. Katherine (1987). Logan's Medical and Scientific Abbreviations. J. B. Lippincott and Company. p. 232. ISBN0-397-54589-4.
- ^'Conduction Disorders'. sitecoreprod.heart.org|beta.heart.org|www.heart.org|heart.org|*.azurewebsites.net|localhost.
- ^Electrophysiology: A Companion Guide, Steinberg (ed.), p. 142
- ^Valentin Fuster; R. Wayne Alexander; Robert A. O'Rourke; Robert Roberts; et al. (November 2000). Hurst's The Heart (10th ed.). McGraw-Hill Professional Publishing. Figure 24â60b. ISBN978-0-07-135695-4.
- ^ abcDorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. 2012. p. 227. ISBN978-1-4160-6257-8.
External links[edit]
Classification |
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Retrieved from 'https://en.wikipedia.org/w/index.php?title=Heart_block&oldid=1005253137'
Other names: Bundle Branch Block; Complete Heart Block Lords of the fallen cell 11.
- Medication List
About Heart Block
Sometimes the signal from the heart's upper to lower chambers is impaired or doesn't transmit. This is 'heart block' or 'AV block.' This does not mean that the blood flow or blood vessels are blocked.
Heart block is classified according to the level of impairment -- first-degree heart block, second-degree heart block or third-degree (complete) heart block.
First-degree heart block
First-degree heart block, or first-degree AV block, is when the electrical impulse moves through the AV node more slowly than normal. The time it takes for the impulse to get from the atria to the ventricles (the PR interval) should be less than about 0.2 seconds. If it takes longer than this, it's called first-degree heart block.
Complete Heart 1 1 Full
Heart rate and rhythm are normal, and there may be nothing wrong with the heart.
Certain heart medicines such as digitalis (DIJ'ih-TAL'is) can slow conduction of the impulse from the atria to the ventricles and cause first-degree AV block. Also, well-trained athletes may have it.
Generally, no treatment is necessary for first-degree heart block.
Second-degree heart block
In this condition, some signals from the atria don't reach the ventricles. This causes 'dropped beats.' On an electrocardiogram, the P wave isn't followed by the QRS wave, because the ventricles weren't activated. Waves aax crack mac. There are two types:
- Type I second-degree heart block, or Molitz Type I, or Wenckebach's AV block. Electrical impulses are delayed more and more with each heartbeat until a beat is skipped. This condition is not too serious but sometimes causes dizziness and/or other symptoms.
- Type II second-degree heart block, or Molitz Type II. This is less common than Type I but generally more serious. Because electrical impulses can't reach the ventricles, an abnormally slow heartbeat may result. In some cases a pacemaker is needed.
Third-degree or complete heart block
Complete heart block (complete AV block) means that the heart's electrical signal doesn't pass from the upper to the lower chambers. When this occurs, an independent pacemaker in the lower chambers takes over. The ventricles can contract and pump blood, but at a slower rate than that of the atrial pacemaker.
These impulses are called functional or ventricular scope beats. They're usually are very slow and can't generate the signals needed to maintain full functioning of the heart muscle. On the electrocardiogram, there's no normal relationship between the P and the QRS waves.
Complete heart block is most often caused in adults by heart disease or as a side effect of drug toxicity. Heart block also can be present at -- or even before -- birth. (This is called congenital heart block.) It also may result from an injury to the electrical conduction system during heart surgery. Complete heart block may be a medical emergency with potentially severe symptoms and a serious risk of cardiac arrest (sudden cardiac death). If a pacemaker can't be implanted immediately, a temporary pacemaker might be used to keep the heart pumping until surgery can be performed.
Note: There are currently no drugs listed for 'Heart Block'.
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