Wolff-Parkinson-White and Atrioventricular (AV) Heart Blocks

Chapters 12 and 17

Wolff-Parkinson-White

Chapter 12

Artrioventricular Bypass Tract

Accessory pathways form and fail to disappear during fetal development

Formed near the mitral or tricuspid valves or interventricular septum

An AV bypass tract is sometimes referred to as the bundle of Kent

Artrioventricular Bypass Tract

From SA node directly to AV node AND to ventricular myocardium

Partially bypassing the bundle of His and purkinje fibers

Accessory Pathways

Wolff-White-Parkinson

Wide QRS

due to early depolarization

not due to a delay in depolarization

Shortened PR interval

Upstroke QRS complex is slurred; delta wave

Wolff-Parkinson-White

As a general rule: the initial QRS complex (delta wave) vector will point away from the area of the ventricles that is first to be stimulated by the bypass tract

F.Y.I.

Wolff-Parkinson-White

Bypass Tracts

Left Lateral

negative delta waves in I and/or aVL and positive in V1

Posterior

positive delta waves in most of the precordial (chest) leads and negative in the inferior leads

Right

negative delta waves in V1 and V2 and positive in I and V6

Anteroseptal (anterior)

negative delta waves in leads V1 and V2

F.Y.I.

WPW Significance

More prone to arrhythmias especially SVT

Often mistaken for RBBB or LBBB or an MI

AV Heart Block

Chapter 17

15

Classification of AV Heart Blocks

Degree AV Conduction Pattern

1St Degree BlockUniformly prolonged PR

interval

2nd Degree, Mobitz Type IProgressive PR interval

prolongation

2nd Degree, Mobitz Type II Sudden conduction failure

3rd Degree Block No AV conduction

First Degree Block

note the prolonged PR interval

Second Degree AV Block

Mobitz type I or Winckebach

Mobitz type II

Second Degree AV Block Type I or Wenckebach

Second Degree AV Block Type I or Wenckebach

1.Progressive lengthening of the PR interval from beat to beat until a beat is dropped.

2.The PR interval after the nonconducted P wave is shorter than the PR interval before the nonconducted P wave.

3.May be grouping of QRS complexes

Second Degree AV BlockType II

1. Sudden appearance of a single, non-conducted sinus P wave...

2. ...without...

1. ...the progressive prolongation of the PR intervals…

2. ...and the shortening of the PR interval in the beat after the non-conducted P wave.

Second Degree AV BlockType II

2:1 AV Blocks

• Often are type II blocks • look for slightly prolonged QRS

• But they can be type I blocks• look at long rhythm strip

• Sometimes they are labeled a “second degree block” only

Advanced Second-Degree AV Block

• Two or more consecutive non-conducted sinus P waves

• Note the consistent PR intervals

Third-Degree (Complete) AV Block

Third-Degree (Complete) AV Block

1. P waves are present, with a regular atrial rate faster than the ventricular rate

2. QRS complexes are present, with a slow (usually fixed) ventricular rate

3. The P wave bears no relation to the QRS complexes, and the PR intervals are completely variable

4. (Some properly timed P waves may be conducted)

Third-Degree (Complete) AV Block

• QRS can be normal width or wide

AV Dissociation

• SA is pacing the atria• AV is pacing the ventricles• Ventricular rate is similar to atria rate• No P wave, even if properly timed, will

be conducted.

AV Dissociation

AV Dissociation

Third-Degree (Complete) AV Block

100 b/min42 b/min

NoComplete heart block