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| {{Infobox_Disease | | {{Infobox_Disease |
| | Name = {{PAGENAME}} | | | Name = {{PAGENAME}} |
| | Image = example2.jpg | | | Image = example2.jpg |
| | Caption =
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| | DiseasesDB = 10477
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| | ICD10 = {{ICD10|I|44|0|i|30}}
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| | ICD9 = {{ICD9|426.11}}
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| | ICDO =
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| | OMIM =
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| | MedlinePlus =
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| | eMedicineSubj =
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| | eMedicineTopic =
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| }} | | }} |
| {{SI}} | | {{First degree AV block}} |
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| {{CMG}}'''; Associate Editor-In-Chief:''' {{CZ}}'''; Assistant Editor-In-Chief:''' Sandeep Krishnan
| | '''For patient information, click [[Heart block (patient information)|here]]''' |
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| ==Overview==
| | {{CMG}}; {{AE}} {{Sara.Zand}} {{CZ}}, {{AEL}}, [[User:Mohammed Salih|Mohammed Salih, M.D.]] |
| '''First degree AV block''' or '''PR prolongation''' is a disease of the [[electrical conduction system of the heart|electrical conduction system]] of the [[heart]] in which the [[PR interval]] is lengthened or prolonged. In first degree heart block, the disease is almost always at the level of the [[atrioventricular node]] (AV node). It has a [[prevalence]] in the normal (young adult) population of 0.65-1.1% and the [[incidence]] is 0.13 per 1000 persons.
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| == Causes ==
| | {{SK}} First degree atrioventricular block, first degree AVB, first-degree atrioventricular block, first-degree AV block, first-degree AVB, 1st degree heart block, 1st degree AV block |
| First degree AV block may be due to conduction delay in the [[AV node]], in the His-Purkinje system (made up by the [[bundle of His]] and the [[Purkinje fibers]]), or a combination of the two. The majority of cases are due to a dysfuction of the [[AV node]]; however, when first degree heart block coexists with a [[bundle-branch block]], the cause is more likely to be a conduction delay in the His-Purkinje system. | |
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| ==Differential Diagnosis of Causes of First Degree AV Block== | | ==[[First degree AV block overview|Overview]]== |
| The most common causes of first degree heart block are an AV nodal disease, enhanced vagal tone (for example in athletes), [[myocarditis]], acute [[myocardial infarction]] (especially acute inferior MI), electrolyte disturbances and [[drugs]]. The drugs that most commonly cause first degree heart block are those that increase the refractory time of the [[AV node]], thereby slowing AV conduction. These include [[calcium channel blockers]], [[beta-blockers]], [[digitalis]] [[cardiac glycosides]] and anything that increases cholinergic activity such as [[cholinesterase inhibitor]]s.
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| ==Diagnosis== | | ==[[First degree AV block historical perspective|Historical Perspective]]== |
| In normal individuals, the [[AV node]] slows the conduction of electrical impulse through the heart. This is manifest on a surface EKG as the PR interval. The normal PR interval is from 120 milliseconds (ms) to 200 milliseconds (ms) in duration. This is measured from the initial deflection of the [[P wave]] to the beginning of the [[QRS complex]].
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| In first degree heart block, the diseased AV node conducts the electrical activity slower. This is seen as a [[PR interval]] greater than 200 milliseconds (ms) in length on the surface EKG. It is usually an incidental finding on a routine EKG.
| | ==[[First degree AV block pathophysiology|Pathophysiology]]== |
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| First degree heart block does not require any particular evaluation except for electrolyte and drug screens especially if an overdose is suspected. | | ==[[First degree AV block causes|Causes]]== |
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| ==Differential Diagnosis of AV Block in General== | | ==[[First degree AV block differential diagnosis|Differentiating First degree AV block from other Diseases]]== |
| ===Normal Variants===
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| # [[PR prolongation]] can be found in 0.5% of healthy patients
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| # [[Second degree block type I]] may be seen in healthy patients during sleep
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| # Transient AV block can occur with vagal maneuvers
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| ===ST Elevation MI=== | | ==[[First degree AV block epidemiology and demographics|Epidemiology and Demographics]]== |
| In acute ST elevation [[MI]]:
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| * [[First degree block]] occurs in 8% to 13%
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| * [[Second degree block]] in 3.5% to 10%
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| * [[Complete heart block]] in 2.5% to 8%
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| ====Inferior ST Elevation MI==== | | ==[[First degree AV block risk factors|Risk Factors]]== |
| * Inferior ST elevation [[MI]]: [[AV block]] is more common in patients with inferior [[MI]]s (1/3rd of patients)
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| # In 90% of patients the inferior wall is supplied by the [[RCA]] which gives off a branch to the [[AV node]]
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| # As a rule the [[AV block]] is transient and normal function returns within a week of the acute episode
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| ====Anterior ST Elevation MI==== | | ==[[First degree AV block screening|Screening]]== |
| * Anterior ST elevation [[MI]]: [[AV block]] may be seen in up to 21%
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| # Incidence of [[second degree AV block]] and [[third degree AV block]] is 5 to 7%
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| # Block is the result of damage to the interventricular septum supplied by the [[LAD]]
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| # There is damage to the bundle branches either in the form of bilateral bundle branch block or [[trifascicular block]]
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| # [[RBBB]], [[RBBB]] + [[LAHB]], [[RBBB]] + [[LPHB]] or [[LBBB]] often appear before the development of [[AV block]]
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| # The PR is normal or minimally prolonged before the onset of [[second degree AV block]] or [[third degree AV block]]
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| # Although the [[AV block]] is usually transient, there is a relatively high incidence of recurrence or high-degree AV block after the acute event
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| # In addition to [[ischemia]], [[fibrosis]] and [[calcification]] of the summit of the ventricular septum that involve the branching part of the bundle branches, may play a role in the genesis of the conduction defect.
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| # It used to be thought that CAD was the most frequent cause of chronic [[complete AV block]], but it actually causes only 15% of cases
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| ===Degenerative Diseases=== | | ==[[First degree AV block natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
| * Sclerodegenerative disease of the bundle branches first described by Lenegre
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| * The pathologic process is called idiopathic bilateral bundle branch fibrosis and the heart block is called primary heart block
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| * This is the most common cause of chronic [[AV block]] (46%)
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| * Lev described similar degenerative lesions, which he referred to as sclerosis of the left side of the cardiac skeleton. There is progressive fibrosis and calcification of the mitral annulus, the central fibrous body, the pars membranacea, the base of the aorta, and the summit of the muscular ventricular septum. Various portions of the [[His bundle]] or the bundle branches may be involved, resulting in [[AV block]].
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| ===Hypertension=== | | ==Diagnosis== |
| * Chronic [[AV block]] in patients with [[HTN]] is thought to be due to [[CAD]] or sclerosis of the left side of the cardiac skeleton exacerbated by [[hypertension]]
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| ===Diseases of the Myocardium===
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| * [[Acute rheumatic fever]]: PR prolongation is a common (25 to 95% of cases) sign in patients with [[acute rheumatic fever]]
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| :# [[Type I second degree AV block]] may occur, but [[complete AV block]] is uncommon
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| :# usually transient, disappears when the patient recovers
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| * [[Amyloidosis]]
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| * [[Ankylosing spondylitis]]
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| * [[Chagas disease]]
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| * [[Dermatomyositis]]
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| * [[Dilated cardiomyopathy]] results in various degrees of heart block are seen in 15% of patients
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| * [[Diphtheria]]
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| * [[HCM]]: 3% of patients with [[HCM]] will develop heart block
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| * [[Hemochromatosis]]
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| * [[Lyme disease]]
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| * [[Muscular dystrophy]]
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| * [[Myocarditis]]
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| * [[Sarcoid]]
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| * [[Scleroderma]]
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| * [[SLE]]
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| * Tumors, primary and secondary
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| ===Valvular Heart Disease===
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| [[Valvular heart disease|Valvular Diseases]]
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| * Calcific [[aortic stenosis]] may be accompanied by chronic partial or complete AV block
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| * There is an extension of the calcification to involve the main bundle or its bifurcation, resulting in degeneration and necrosis of the conduction tissue
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| * May also occur in rheumatic mitral valve disease, but is less common
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| * Occasionally, massive calcification of the mitral annulus as an aging process may cause [[AV block]]
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| * May also be seen in [[bacterial endocarditis]], especially of the [[aortic valve]]
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| ===Drugs===
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| * [[Digoxin]] is one of the most common causes of reversible [[AV block]]
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| :# When [[second degree AV block]] is induced, it is always of the Type I variety
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| :# When complete block occurs, the [[QRS complex]]es are narrow because the block is of the AV node
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| :# The ventricular response rate is more rapid than that due to organic lesions, and increased automaticity of the AV junctional pacemaker may be responsible.
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| * [[Quinidine]] and [[Procainamide]] may produce slight prolongation of the PR
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| * [[Beta blocker|β blockers]] may cause [[AV block]]
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| * [[Diltiazem]] and [[verapamil]] may cause AV conduction delay and [[PR interval]] prolongation
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| ===Congenital===
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| * Occurs in the absence of other evidence of organic heart disease
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| * Site is usually proximal to the bifurcation of the [[His bundle]], most often in the [[AV node]]
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| * Narrow [[QRS]] with a rate > 40 beats per minute
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| * Frequently seen in those with corrected [[transposition of the great vessels]], and occasionally in [[ASD]]s and [[Ebstein's anomaly]]
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| ===Trauma===
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| * May be induced during open heart surgery in the area of AV conduction tissue
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| * Seen in patients operated on for the correction of [[VSD]], [[tetralogy of Fallot]], and [[endocardial cushion defect]].
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| * May be due to [[edema]], transient ischemia, or actual disruption of the conduction tissue. The block may therefore be permanent or transient.
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| * Also reported with both penetrating and non-penetrating trauma of the chest
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| ==Electrocardiographic Findings==
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| # [[PR interval]] is greater than 0.20 seconds = 200 miliseconds
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| # Each [[P wave]] is followed by a [[QRS]]
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| # Range of [[PR interval]] is between 0.21 and 0.40 seconds
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| # [[P wave]] may be mistaken for a [[T wave]] or a [[U wave]]
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| # The [[PR interval]] is more variable in those without heart disease
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| # In patients with a narrow [[QRS]], His-Bundle recordings show that the conduction delay is in the AV node, with prolongation of the atrial His (AH) time, rarely is a prolonged His ventricular (HV) time responsible.
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| # In patients with PR prolongation and QRS prolongation, then the conduction delay may occur in various regions of the conduction system
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| == Treatment ==
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| The management includes identifying and correcting electrolyte imbalances and withholding any medications that are associated with PR prolongation. This condition does not require admission unless there is an associated [[myocardial infarction]]. Even though it usually does not progress to higher forms of heart block, it may require outpatient follow up and monitoring of the [[EKG]] especially if there is an associated [[bundle branch block]]. If there is a need for treatment of an unrelated condition care should be taken not to introduce any medication that may slow AV conduction. If this is not feasible, clinicians should be very cautious when introducing any drug that may slow conduction and if drugs are introduced, regular monitoring of the [[EKG]] is indicated.
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| == Prognosis ==
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| Isolated first degree heart block has few if any clinical consequences. There are no symptoms or signs associated with it, and there is little danger of progression to [[complete heart block]].
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| Individuals who have first degree block as part of a triad of first degree heart block, [[right bundle branch block]], and either [[left anterior fascicular block]] or [[left posterior fascicular block]] (known as [[trifascicular block]]) may be at an increased risk of progression to [[complete heart block]].
| | [[First degree AV block history and symptoms|History and Symptoms ]] | [[ First degree AV block physical examination|Physical Examination]] | [[First degree AV block laboratory findings|Laboratory Findings]] | [[First degree AV block electrocardiogram|Electrocardiogram]] | [[First degree AV block EKG examples|EKG Examples]] | [[First degree AV block chest x ray|Chest X Ray]] | [[First degree AV block echocardiography|Echocardiography]] | [[First degree AV block other imaging findings|Other Imaging Findings]] | [[First degree AV block other diagnostic studies|Other Diagnostic Studies]] |
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| ==Diagrams & Examples== | | ==Treatment== |
| | [[First degree AV block medical therapy|Medical Therapy]] | [[First degree AV block surgery |Surgery]] | [[First degree AV block primary prevention|Primary Prevention]] | [[First degree AV block secondary prevention|Secondary Prevention]] | [[First degree AV block cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[First degree AV block future or investigational therapies|Future or Investigational Therapies]] |
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| <div align="left">
| | ==Case Studies== |
| <gallery heights="175" widths="175">
| | [[First degree AV block case study one|Case #1]] |
| Image:example3.jpg|
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| Image:example4.jpg|
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| </gallery>
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| </div>
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| <div align="left">
| | ==Related Chapters== |
| <gallery heights="175" widths="175">
| | *[[Electrical conduction system of the heart]] |
| Image:example1.jpg|
| | *[[Electrocardiogram]] (ECG or EKG) |
| Image:FirstAVblock.jpg|
| | *[[SA node]] |
| </gallery>
| | *[[AV node]] |
| </div>
| | *[[Second degree AV block]] |
| | *[[Third degree AV block]] |
| | *[[Bundle branch block]] |
| | *[[Hemiblock]] |
| | *[[Infra-Hisian Block]] |
| | *[[Left anterior fascicular block]] |
| | *[[Left posterior fascicular block]] |
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| [[Category:Electrophysiology]] | | [[Category:Arrhythmia]] |
| [[Category:Cardiology]] | | [[Category:Cardiology]] |
| [[Category:Disease]] | | [[Category:Disease]] |
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| [[Category:Emergency medicine]] | | [[Category:Emergency medicine]] |
