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| {{CMG}}; {{AE}} {{CZ}} | | {{CMG}}; {{AE}} {{CZ}} |
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| | ==[[Second degree AV block overview|Overview]]== |
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| | ==[[Second degree AV block historical perspective|Historical Perspective]]== |
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| | ==[[Second degree AV block pathophysiology|Pathophysiology]]== |
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| ==Electrocardiographic Findings== | | ==[[Second degree AV block causes|Causes]]== |
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| ====Type I Second Degree AV Block==== | | ==[[Second degree AV block differential diagnosis|Differentiating Second degree AV block from other Diseases]]== |
| * Also called the [[Wenckebach phenomenon]] or [[Mobitz type I]] block
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| * Intermittent failure of the supraventricular impulse to be conducted to the ventricles, not every [[P wave]] is followed by a [[QRS]]
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| * There is progressive prolongation of the [[PR interval]] until a [[P wave]] is blocked
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| * Progressive shortening of the RR interval until a [[P wave]] is blocked
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| * The RR interval containing the blocked [[P wave]] is shorter than the sum of 2 PP intervals
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| * The increase in the [[PR interval]] is longest in the second conducted beat after the pause
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| * These rules may not be followed because of fluctuation in vagal tone and secondary to sinus arrhythmia.
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| * In patients with normal [[QRS]] width, the block is usually located in the [[AV node]]
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| :*there is progressive prolongation of the AH interval until the blocked [[P wave]] occurs
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| * When it is associated with bundle branch block, the block may occur in the [[AV node]], [[His bundle]] or the contralateral bundle branch
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| :*in 75% the block is in the [[AV node]]
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| :*in 25% it is infranodal <br>
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| | ==[[Second degree AV block epidemiology and demographics|Epidemiology and Demographics]]== |
| Shown below is a two lead rhythm strip from a patient in the emergency room. The [[Sinus rhythm|rhythm is sinus]] with second degree A/V block. Note the progressive lengthening of the [[PR interval]] and that the interval that brackets the blocked P wave is less than twice that of the [[RR interval]]. This recording suggests a Mobitz I A/V block, but some care has to be taken as the [[QRS]] that ends the pause in at least one case looks like a nodal escape beat.
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| [[File:Second degree AV block.jpg|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an image of an electrocardiogram showing type I second degree AV block (Wenckebach).
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| [[File:Wenckebach.png|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia,http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an electrocardiogram showing type I second degree AV block (Wenckebach).
| | ==[[Second degree AV block risk factors|Risk Factors]]== |
| [[File:Wenckebach2.png|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia,http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an electrocardiogram showing type I second degree AV block (Wenckebach).
| | ==[[Second degree AV block natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
| [[File:Wenckebach3.jpg|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia,http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an electrocardiogram showing type I second degree AV block (Wenckebach).
| | ==Diagnosis== |
| [[Image:Wenckebach_2.jpg|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia,http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an electrocardiogram showing a Mobitz I A/V block with a gradual increase in the [[PR interval]] before the dropped [[p wave]]
| | [[Second degree AV block history and symptoms|History and Symptoms ]] | [[ Second degree AV block physical examination|Physical Examination]] | [[Second degree AV block laboratory findings|Laboratory Findings]] | [[Second degree AV block electrocardiogram|Electrocardiogram]] | [[Second degree AV block EKG examples|EKG Examples]] | [[Second degree AV block chest x ray|Chest X Ray]] | [[Second degree AV block echocardiography|Echocardiography]] | [[Second degree AV block other imaging findings|Other Imaging Findings]] | [[Second degree AV block other diagnostic studies|Other Diagnostic Studies]] |
| [[File:MobitzIAVBlock.jpg|center|500px]] | |
| Copyleft image obtained courtesy of ECGpedia,http://en.ecgpedia.org/wiki/Main_Page
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| ====Type II Second-Degree AV Block: [[Mobitz Type II Block]]==== | | ==Treatment== |
| * There are intermittent blocked [[P wave]]s
| | [[Second degree AV block medical therapy|Medical Therapy]] | [[Second degree AV block surgery |Surgery]] | [[Second degree AV block primary prevention|Primary Prevention]] | [[Second degree AV block secondary prevention|Secondary Prevention]] | [[Second degree AV block cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Second degree AV block future or investigational therapies|Future or Investigational Therapies]] |
| * In the conducted beats, the [[PR interval]]s remain constant
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| * The PR is fairly constant except that slight shortening may occur in the first beat after the blocked cycle. This is the result of improved conduction following the block
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| * Most patients with type II second-degree AV block have associated bundle branch block.
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| * In these instances the block is usually located distal to the [[His bundle]], in approximately 27 to 35% of patients however, the lesion is located in the His bundle itself, and a narrow complex may be inscribed. <br>
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| *'''''2:1 AV Block:'''''
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| :*Impossible to determine whether the second-degree AV block is type I or type II.
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| :*A long rhythm strip is helpful to document any change in the behavior of the conduction ratio
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| :*When the atrial rate is increased by exercise or by [[atropine]], the AV block in type I tends to decrease and that in type II tends to increase
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| Shown below is an electrocardiogram of a 12 lead EKG with a 2:1 AV block.
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| [[File:2to1AVBlock1.jpg|center|500px]] | |
| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| ----
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| Shown below is an electrocardiogram of a type II second degree AV block (Mobitz type II).
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| [[File:Rhythm Mobitz.png|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| Shown below is an electrocardiogram of a 3 channel recording with a 2:1 AV block in a 73 year old woman with [[dizziness]]. 2 to 1 AV block (every other [[P wave]] is conducted to the [[ventricles]]) 2 to 1 AV block starts after the 5th [[QRS]] in this 3 channel recording. The first non-conducted [[P wave]] is indicated with an arrow. Note the [[long PR interval]] of conducted [[P waves]] is constant and the [[left bundle branch block]] 2 to 1 AV block cannot be classified into Mobitz type I or II as we do not know if the 2nd [[P wave]] would be conducted with the same or [[longer PR interval]]. [[File:2_to_1_AV_block.jpg|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| Shown below is an electrocardiogram of a 2:1 AV Block with [[atrial tachycardia]].
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| [[File:2to1AVBlock2.jpg|center|500px]]
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| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| Shown below is an example of EKG showing two strips from the same patient with a 2:1 block on the top tracing and a Mobitz II A/V block on the lower one. Note that with 2:1 block you cannot tell if this is a Mobitz I or II. Mobitz II is seen below as the PR does not change before and after the non-conducted [[P wave]].
| | ==Case Studies== |
| [[Image:Mobitz_II_AV_block.jpg|center|500px]] | | [[Second degree AV block case study one|Case #1]] |
| Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
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| ====Advanced AV Block or High Grade AV Block====
| | ==Related Chapters== |
| * When the AV conduction ratio is 3:1 or higher
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| * In some cases only occasional ventricular captures are observed, and the dominant rhythm is maintained by a subsidiary [[pacemaker]].
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| * You must compare the PR interval of the rare captured beats, a constant PR interval suggests type II block <br>
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| ==Differential Diagnosis of AV Block==
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| ===Differential Diagnosis of Second-Degree AV Block===
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| * Second Degree AV Block may be simulated by blocked PACs. Must be very careful to assure that the P to P intervals are constant
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| * 2:1 conduction may simulate [[sinus bradycardia]] as the blocked [[P wave]]s may fall on the preceding [[T wave]]s <br>
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| ===Differential Diagnosis of AV Block in General===
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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====
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| *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=====
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| *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=====
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| * 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====
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| * 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====
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| * 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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| ==History and Symptoms==
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| Most people with Wenckebach (Type I Mobitz) do not show symptoms. However, those that do usually display one or more of the following:
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| *[[Light-headedness]]
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| *[[Dizziness]]
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| *[[Fainting]]
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| *[[Fatigue]]
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| *[[Heart failure]] symptoms
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| *[[Pre-syncope]]
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| *[[Syncope]]
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| ==Treatment==
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| ===Mobitz I===
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| * Patients are usually asymptomatic and doesn't require a pacemaker.
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| * Correction of reversible causes of the block such as ischemia, medications, and vagotonic conditions should be addressed.
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| ===Mobitz II===
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| * Correction of reversible causes of the block such as ischemia, medications, and vagotonic conditions should be considered.
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| * Implantation of permanent pacemakers in both asymptomatic and symptomatic patients is usually done. Asymptomatic Mobitz II are prone to be converted to symptomatic or third degree heart AV block. Thus, they should be considered for a pacemaker even if asymptomatic.
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| * A dual chamber DDD pacemaker is preferred over a single chambered VVI pacemakers as it maintains physiologic AV synchrony.
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| * 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 and to record instances of [[atrial flutter]] and [[atrial fibrillation]]
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| * Treatment may also include medicines to control [[blood pressure]] and [[atrial fibrillation]], as well as lifestyle and dietary changes to reduce risk factors associated with [[myocardial infarction|heart attack]] and [[stroke]].
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| * Treatment in emergency situations are [[atropine]] and an [[external pacer]].
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| ==Related chapters== | |
| *[[Electrical conduction system of the heart]] | | *[[Electrical conduction system of the heart]] |
| *[[Electrocardiogram]] (ECG or EKG) | | *[[Electrocardiogram]] (ECG or EKG) |
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| *[[First degree AV block]] | | *[[First degree AV block]] |
| *[[Third degree AV block]] | | *[[Third degree AV block]] |
| ==Sources==
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| *Copyleft images obtained courtesy of ECGpedia, http://en.ecgpedia.org/index.php?title=Special:NewFiles&dir=prev&offset=20080806182927&limit=500
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| *{{WhoNamedIt|synd|2824}}
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| * http://www.youtube.com/watch?v=GVxJJ2DBPiQ - AV Block Parody Video by the University of Alberta
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| *[http://www.emedicine.com/emerg/topic234.htm Emergency Cardiovascular Medicine] - eMedicine article on 2nd Degree Heart Block
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| ==References== | | ==References== |
