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{{Infobox_Disease |
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{{Paroxysmal AV block}}
  Image          = P4block.jpg|
'''For patient information, click [[Xyz (patient information)|here]]'''
  Caption        = Phase 4 block in the His-Purkinje system occurring after an atrial premature beat that conducts to the ventricles.  Notice the delayed sinus beat that results in a critical P-P lengthening with subsequent Phase 4 block in the His.|
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'''Paroxysmal AV block''' or ''phase 4 block'' is a condition when 1:1 AV conduction suddenly changes to complete AV block.
==[[Paroxysmal AV block overview|Overview]]==


==Mechanism of phase 4 block==
==[[Paroxysmal AV block historical perspective|Historical Perspective]]==


# Cells electrically capable of pacing slowly reduce their transmembrane potential during phase 4 of the action potential
==[[Paroxysmal AV block classification|Classification]]==
# When the time of diastole is prolonged, cells may reduce their membrane potential below that capable of conducting (below -65 mV)
# With reduction in cycle length, the membrane threshold potential decreases toward zero resulting in inability to excite that tissue.  Hence this phenomena is also referred to as "bradycardia dependent block"


==Most often occurs after critical lengthening of PP interval often following:==
==[[Paroxysmal AV block pathophysiology|Pathophysiology]]==
# APD eithers conducted or non conducted - [[Paroxysmal AV block#Figure 1|Figure 1]]
# Retrogradely conducted VPBs - [[Paroxysmal AV block#Figure 2|Figure 2]]
# His bundle extrasystole retrogradely conducts to atrium but with block to the ventricle during CMS
# Vagal maneuvers, such as valsalva and carotid sinus massage - [[Paroxysmal AV block#Figure 3|Figure 3]]


==Characteristics of Paroxysmal AV block==
==[[Paroxysmal AV block causes|Causes]]==
# Occurs after critical lengthening of PP interval
# Localized to sub AV node
# Mechanism is phase 4 block
# Dangerous because of unreliable escape mechanism
# Paroxysmal and often difficult to diagnose


==Phase 4 Block, Figure 1==
==[[Paroxysmal AV block differential diagnosis|Differentiating Paroxysmal AV block from other Diseases]]==
[[Image:P4block.jpg|600px|]]
*Phase 4 block in the His-Purkinje system occurring after an atrial premature beat that conducts to the ventricles.  Notice the delayed sinus beat that results in a critical P-P lengthening with subsequent Phase 4 block in the His.
==Figure 2==
[[Image:P4block2.jpg|600px|]]
*Complete AV block following a ventricular premature beat that conducts to the atrium.  The following sinus beat results in a long P-P interval.  Given the baseline RBBB, left anterior hemiblock, phase 4 block likely occurs in the left posterior fascicle.
==Figure 3==
[[Image:P4block3.jpg|600px|]]
*Carotid massage resulting in complete AV block.  Although this maneuver most often results in block in AV node, this likely results from phase 4 block infranodally.  Note the lengthening of the P-P interval with no increase in PR interval.


==References==
==[[Paroxysmal AV block epidemiology and demographics|Epidemiology and Demographics]]==
#Wellens, Hein J.J., Conover, Mary.  The ECG in Emergency Decision Making.  Saunders Elsevier, St. Louis.  2006
#Intermittent atrioventricular block: What is the mechanism? Rakesh K. Pai, MD, Marcos Daccarett, MD, Nathan M. Segerson, MD, Moeen Abedin, MD, T. Scott Wall, MD, Roger A. Freedman, MD, Mohamed H. Hamdan, MD. Heart Rhythm December 2006. pp. 1502


==[[Paroxysmal AV block risk factors|Risk Factors]]==


{{Electrocardiography}}
==[[Paroxysmal AV block screening|Screening]]==
{{Circulatory system pathology}}
 
==[[Paroxysmal AV block natural history, complications and prognosis|Natural History, Complications and Prognosis]]==
 
==Diagnosis==
[[Paroxysmal AV block diagnostic study of choice|Diagnostic study of choice]] | [[Paroxysmal AV block history and symptoms|History and Symptoms]] | [[Paroxysmal AV block physical examination|Physical Examination]] | [[Paroxysmal AV block laboratory findings|Laboratory Findings]] | [[Paroxysmal AV block electrocardiogram|Electrocardiogram]] | [[Paroxysmal AV block x ray|X-Ray Findings]] | [[Paroxysmal AV block echocardiography and ultrasound|Echocardiography and Ultrasound]] | [[Paroxysmal AV block CT scan|CT-Scan Findings]] | [[Paroxysmal AV block MRI|MRI Findings]] | [[Paroxysmal AV block other imaging findings|Other Imaging Findings]] | [[Paroxysmal AV block other diagnostic studies|Other Diagnostic Studies]]
 
==Treatment==
[[Paroxysmal AV block medical therapy|Medical Therapy]] | [[Paroxysmal AV block interventions|Interventions]] | [[Paroxysmal AV block surgery|Surgery]] | [[Paroxysmal AV block primary prevention|Primary Prevention]] | [[Paroxysmal AV block secondary prevention|Secondary Prevention]] | [[Paroxysmal AV block cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Paroxysmal AV block future or investigational therapies|Future or Investigational Therapies]]
 
==Case Studies==
[[Paroxysmal AV block case study one|Case #1]]


[[Category:Cardiac electrophysiology]]
[[Category:Cardiology]]
[[Category:Cardiology]]
[[Category:Cardiovascular diseases]]
[[Category:Arrythmia]]
[[Category:Emergency medicine]]
[[Category:Disease]]
[[Category:Up-To-Date]]
[[Category:Up-To-Date cardiology]]


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Revision as of 02:40, 18 May 2020

Paroxysmal AV block Microchapters

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Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Paroxysmal AV block from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Study of Choice

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

X-ray

Echocardiography and Ultrasound

CT scan

MRI

Other Imaging Findings

Other Diagnostic Studies

Treatment

Medical Therapy

Interventions

Surgery

Primary Prevention

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Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Akash Daswaney, M.B.B.S[2]

Synonyms and keywords:

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Paroxysmal AV block from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic study of choice | History and Symptoms | Physical Examination | Laboratory Findings | Electrocardiogram | X-Ray Findings | Echocardiography and Ultrasound | CT-Scan Findings | MRI Findings | Other Imaging Findings | Other Diagnostic Studies

Treatment

Medical Therapy | Interventions | Surgery | Primary Prevention | Secondary Prevention | Cost-Effectiveness of Therapy | Future or Investigational Therapies

Case Studies

Case #1


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