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| | Name = {{PAGENAME}} | | | Name = {{PAGENAME}} |
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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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| {{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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| {{SK}} Prolonged PR; PR prolongation; prolonged PR interval; long PR; PR interval lengthened; first-degree AV block; first-degree AVB; first-degree atrioventricular block | | {{CMG}}; {{AE}} {{Sara.Zand}} {{CZ}}, {{AEL}}, [[User:Mohammed Salih|Mohammed Salih, M.D.]] |
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| ==Overview==
| | {{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 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]]). | |
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| ==Pathophysiology== | | ==[[First degree AV block overview|Overview]]== |
| First degree AV block may be due to conduction delay in the [[AV node]], 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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| ==Causes of AV Block== | | ==[[First degree AV block historical perspective|Historical Perspective]]== |
| ==Common Causes of First Degree AV Block==
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| 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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| ===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 pathophysiology|Pathophysiology]]== |
| 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 causes|Causes]]== |
| * 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 differential diagnosis|Differentiating First degree AV block from other Diseases]]== |
| * 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 epidemiology and demographics|Epidemiology and Demographics]]== |
| * 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=== | | ==[[First degree AV block risk factors|Risk Factors]]== |
| * 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=== | | ==[[First degree AV block screening|Screening]]== |
| * [[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=== | | ==[[First degree AV block natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
| [[Valvular heart disease|Valvular Diseases]] | |
| * 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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| *[[Ebstein's anomaly]] may be associated with first-degree AV block.
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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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| ==Epidemiology and Demographics==
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| ===Incidence===
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| The [[incidence]] of first degree AV block is 13 per 100,000 persons.
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| ===Prevalence===
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| First degree AV block has a [[prevalence]] in the normal (young adult) population of 65-110 per 100,000.
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| == Natural History, Complications and Prognosis ==
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| ===Natural History===
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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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| ===Complications===
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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]].
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| ==Diagnosis== | | ==Diagnosis== |
| 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.
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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.
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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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| ===EKG examples===
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| This is an [[electrocardiogram]], a 64 year-old man with a history of [[coronary artery disease]]. The patient was taking [[amiodarone]], [[metoprolol]], and [[Vasotec]] at the time of this recording. This was a routine recording. The [[electrocardiogram]] shows [[sinus rhythm]] with a prolonged P wave > 120 milliseconds. The [[P wave]] is notched in the inferior leads. This is consistent with a left atrial abnormality. The [[PR interval]] is long at 200 milliseconds and is diagnostic of [[first-degree heart block]]. The [[Q waves]] in the Interior leads suggest an [[inferior wall infarction]].
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| [[Image:First degree heart block.jpg|center|800px]]
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| This is an [[electrocardiogram]] from a 77 year old man with a history of [[coronary artery disease]]. He was taking [[Monopril]], [[metoprolol]], [[ASA]] and [[ Hytrin]]. The cardiogram shows sinus rhythm with a marked [[first degree heart block]] ( about 360ms). There is also a [[poor R wave progression]] across the precordial leads and a [[Q wave]] in V2 suggestive of a previous [[anterior wall infarction]]. The [[QRS]] also has a left axis deviation best described as a left anterior hemi-block.
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| [[Image:First degree heart block1.jpg|center|800px]]
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| This is an [[electrocardiogram]] from a 87 year old man with a history of [[atrial fibrillation]]. His medications were [[coumadin]] and [[Monopril]]. The cardiogram shows sinus rhythm with rate of about 50/min, and a marked [[first degree heart block]] with a [[pr interval]] of about 350ms.
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| The first complex on the left is a fusion between the patient's native [[QRS]] and the pacemaker spike (this is nomal operation) this is followed by a [[PVC]]. Note the small blip following the [[PVC]] is artifact and is not a failure to capture of the [[pacemaker]]. The [[pacemaker]] is working well as a VVI pacer set at 50/min. The large spikes suggest a unipolar lead.
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| [[Image:First degree heart block2.jpg|center|800px]]
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| The recording below shows sinus rhythm with first degree heart block (pr > 200ms.) Note the [[P wave]]s in the inferior leads are greater than 120 ms. in duration, which suggests left atrial abnormality.
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| [[File:First degree AV block.jpg|center|800px]]
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| The rhythm is sinus. The [[PR interval]] is prolonged (>200ms) and the QRS is a left ward axis (<-30 degrees).
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| The EKG shows a first degree heart block and a left anterior fascicular block.
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| [[File:First degree AV block left ant fasc. block.jpg|center|800px]]
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| Shown below is an electrocardiogram of first degree AV block.
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| [[File:example1.jpg|center|center|800px]]
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| Shown below is an electrocardiogram of first degree AV block.
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| [[File:FirstAVblock.jpg|center|800px]]
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| The EKG shown below is a regular rhythm at a rate of 65/min. The PR interval is 400 ms, the QRS is approximately 110 MS, and there are Qs waves in I, II, aVL, and poor R waves in the precordial leads. This is sinus rhythm with a marked first degree heart block. The QRS suggests an extensive anterior/lateral [[myocardial infarction]].
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| [[Image:1dhb.jpg|center|800px]]
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| The EKG recording below shows sinus rhythm with a marked first degree heart block. In this case the PR interval is about 400 ms. A Holter monitor showed second degree but not third degree A/V block.
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| [[Image:Fdhb.jpg|center|800px]]
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| The EKG below shows first degree AV block
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| [[Image:First degree AV block9.png|center|800px]]
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| Shown below is an EKG showing sinus rhythm with a first degree A/V block (>200ms). There is terminal P wave negativity in V1 suggestive of left atrial abnormality. There is left anterior fascicular block (axis < -30 degrees). The ST segment is slightly elevated in leads II and aVF with T wave inversion suggesting inferior ischemia or infarction.
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| [[Image:First_Degree_AV_Block1.jpg|center|800px]]
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| Shown below is an EKG showing a first degree heart block with a left anterior hemi-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]] |
| [[File:First_degree_heart_block6.jpg|center|800px]] | |
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| Shown below is an example of EKG showing a sinus rhythm with a prolonged PR interval (>120ms.) which is first degree A/V block. There is also a left axis deviation (axis between -30 and -90 degrees) with R waves in the inferior leads. This axis deviation is consitent with a left anterior fasicular block.
| | ==Treatment== |
| [[File:AVBlockEKG.jpg|center|800px]] | | [[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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| == Treatment == | | ==Case Studies== |
| * Correction of reversible causes of the block such as ischemia, medications, electrolyte imbalances, and vagotonic conditions should be considered.
| | [[First degree AV block case study one|Case #1]] |
| * Treatment in emergency situations are [[atropine]] and an [[external pacer]].
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| * Implantation of permanent pacemakers is not usually indicated in first degree heart block.
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| * 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]].
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| * There are some special situations in which placement of a permanent pacemaker is indicated in first degree heart blocks.
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| * Special situations when placement of permanent pacemakers is indicated in first degree heart block are: pacemaker syndrome (loss of atrioventricular synchrony) and in some neuromuscular conditions associated with first degree heart block such as myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb's dystrophy (limb-girdle), and peroneal muscular atrophy)
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| * A dual chamber DDD pacemaker is preferred over a single chambered VVI pacemakers as it maintains physiologic AV synchrony. A dual-chamber [[artificial pacemaker]] is a type of device that typically listens for a pulse from the SA node and sends a pulse to the AV node at an appropriate interval, essentially completing the connection between the two nodes. Pacemakers in this role are usually programmed to enforce a minimum heart rate.
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| ==Sources== | | ==Related Chapters== |
| | | *[[Electrical conduction system of the heart]] |
| Copyleft images obtained courtesy of ECGpedia, http://en.ecgpedia.org/index.php?title=Special:NewFiles&dir=prev&offset=20080806182927&limit=500
| | *[[Electrocardiogram]] (ECG or EKG) |
| | | *[[SA node]] |
| ==References==
| | *[[AV node]] |
| {{Reflist|2}}
| | *[[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]] |
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