Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Chapter 7 Heart Blocks

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Heart Blocks AV Blocks  First Degree  Second Degree  Type I  Wenckebach  Type II  2:1 AV block  High-grade AV block  Third Degree Mechanism of Block  Not a true block  Delay at the AV node  Each impulse is eventually conducted  Intermittent block; some beats are conducted, others are blocked  Pathology can be within the AV node or below it in the Bundle of His  Pathology is often blended with other types of blocks  Atria and ventricles are completely dissociated  There is a total block at the AV node

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ First Degree Heart Block AV node holds each impulse longer than normal before conducting it to the ventricles. Each impulse is eventually conducted.

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ First Degree Heart Block  Regularity: Depends on underlying rhythm  Rate: Depends on underlying rhythm  P Wave: Upright and uniform; each P wave followed by QRS complex  PRI: Greater than.20 seconds; constant across strip  QRS: Less than.12 seconds

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ First Degree Heart Block

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Blocked P Waves

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Type II Second Degree Heart Block AV node selectively conducts some beats but blocks others. Even beats that are conducted can encounter delays in AV node. Conduction through the ventricles is normal.

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Conduction Ratios in Type II Second Degree Heart Block

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Conduction Ratios in Type II Second Degree Heart Block

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Type II Second Degree Heart Block with a Prolonged PRI

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Rules for Type II Second Degree Heart Block  Regularity: If conduction ratio is consistent, R-R interval will be constant, and rhythm will be regular. If conduction ratio varies, R-R will be irregular.  Rate: Atrial rate is usually normal. Since many atrial impulses are blocked, ventricular rate is usually bradycardic (often one-half, one-third, or one-fourth the atrial rate).  P Wave: Upright and uniform; always outnumber QRS complexes.  PRI: Constant on conducted beats, but possibly prolonged.  QRS: Less than.12 seconds.

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Type I Second Degree Heart Block (Wenckebach) Sinus impulses encounter progressive delays in AV node until one impulse is blocked completely and the cycle starts over. Conducted impulses depolarize ventricles normally.

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Classical Second Degree Heart Block  Regularity: Can be regular or irregular, depending on whether conduction ratio varies or is constant  Rate: Usually in bradycardia range; can be one half to one third the normal rate  P Wave: Upright and uniform; more than one P wave for every QRS complex; P-P interval is regular  PRI: Constant on conducted beats; can be greater than.20 seconds  QRS: Less than.12 seconds

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Conduction Pattern in Wenckebach

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Wenckebach  Regularity: Irregular; R-R interval changes as PR interval gets longer; characteristic grouped beating  Rate: Usually slightly slower than normal  P Wave: Upright and uniform; some P waves not followed by QRS complexes  PRI: Progressively lengthens until one P wave is not conducted  QRS: Less than.12 seconds

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Wenckebach

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Complete Heart Block The AV node blocks all sinus impulses, so an escape pacemaker from the AV junction or ventricles takes over to pace the ventricles. Atria and ventricles are totally dissociated.

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ

Complete Heart Block  Regularity: Regular  Rate:40–60 beats per minute if focus is junctional 20–40 beats per minute if focus is ventricular  P Wave: Upright and uniform; more P waves than QRS complexes  PRI: No relationship between P waves and QRS complexes; P waves occasionally superimposed on QRS complexes  QRS: Less than.12 seconds if focus is junctional;.12 seconds or more if focus is ventricular

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Complete Heart Block

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ The Heart Blocks P-PR-RPRIConduction First DegreeRegularUsually Regular >.20 Seconds, constant One P wave for every QRS complex Second Degree Wenckebach Type II Regular Irregular Usually Regular Increasingly longer until one P wave is blocked Constant when conducted (may be prolonged) More P waves than QRS complexes Third DegreeRegular No relation between P waves and QRS complexes More P waves than QRS complexes

Gail Walraven, Basic Arrhythmias, Sixth Edition ©2006 by Pearson Education, Inc., Upper Saddle River, NJ Chapter 7 Practice Strips

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