Second degree AV block pathophysiology

Jump to: navigation, search

Second degree AV block Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Second degree AV block from other Diseases

Epidemiology and Demographics

Risk Factors

Natural History, Complications and Prognosis

Diagnosis

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

EKG Examples

Chest X Ray

Echocardiography

Other Imaging Findings

Other Diagnostic Studies

Treatment

Medical Therapy

Surgery

Primary Prevention

Secondary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Second degree AV block pathophysiology On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

slides

Images

American Roentgen Ray Society Images of Second degree AV block pathophysiology

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Second degree AV block pathophysiology

CDC on Second degree AV block pathophysiology

Second degree AV block pathophysiology in the news

Blogs on Second degree AV block pathophysiology

Directions to Hospitals Treating Second degree AV block

Risk calculators and risk factors for Second degree AV block pathophysiology

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

Please help WikiDoc by adding more content here. It's easy! Click here to learn about editing.

Pathophysiology

Mobitz Type I

The classic site of block in Mobitz type I second degree block is the AV node (70%-75%). In the remaining 25%-30% of the cases the site is infra-nodal (His bundle, bundle branches or fascicles). Mobitz type I is again composed of two variations which show Wenckebach periodicity: classic and atypical.

Classic

Classic variety usually occurs within the AV node. It can be observed in antegrade AV conduction and also in retrograde VA conduction across the AV node. There is a gradually increasing PR interval and eventually a dropped beat. There is also usually a gradually decreasing R-R interval. The PR interval is usually shortest in the initial beat and gradually increases ending in a dropped beat and the cycle repeats. If the interval between the last conducted beat and the first beat of the next cycle is very long, the first beat may be a junctional escape rhythm rather than a conducted beat. This classic Wenckebach phenomenon occurs usually with ratios of 3:2, 4:3 or 5:4. This results in grouped beating.

Atypical

This variant of Wenckebach pattern is defined as long Wenckebach and is also called pseudo-Mobitz type II pattern as it simulates Mobitz type II block. In this pattern the conduction ratios usually exceed 6:5 or 7:6 and the last few beats of the cycle, before a dropped beat, show a relatively constant PR interval (maximum variation of 0.02 sec among them). The beats after the dropped beat again show gradually prolonging PR intervals.[1]

Mobitz Type II

Conduction delay in Mobitz type II second degree block is almost always infra-nodal (His bundle [20%], bundle branches or fascicles). Usually the morphology of the QRS complex is wide, except when the site of block is the His bundle. In this variant of second degree heart block the PR interval is constant with occasional dropped beats as compared to the gradually prolonging PR interval in Mobitz type I. Bifascicular or trifascicular disease is seen in two thirds of the patients with Mobitz type II.

References

  1. El-Sherif N, Aranda J, Befeler B, Lazzara R (1978). "Atypical Wenckebach periodicity simulating Mobitz II AV block". Br Heart J. 40 (12): 1376–83. PMC 483582. PMID 737095. Unknown parameter |month= ignored (help)

Linked-in.jpg