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 F.Y.I. 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

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 Block Uniformly prolonged PR interval 2nd Degree, Mobitz Type I Progressive 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 Progressive lengthening of the PR interval from beat to beat until a beat is dropped. The PR interval after the nonconducted P wave is shorter than the PR interval before the nonconducted P wave. May be grouping of QRS complexes

Second Degree AV Block Type II Sudden appearance of a single, non- conducted sinus P wave... ...without... ...the progressive prolongation of the PR intervals… ...and the shortening of the PR interval in the beat after the non-conducted P wave.

Second Degree AV Block Type 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 P waves are present, with a regular atrial rate faster than the ventricular rate QRS complexes are present, with a slow (usually fixed) ventricular rate The P wave bears no relation to the QRS complexes, and the PR intervals are completely variable (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/min 42 b/min No Complete heart block