“ “ Heart Blocks”Heart Blocks”

Why does AVB occur?Why does AVB occur?

Disease of the atrioventricular nodeDisease of the atrioventricular node

A change in the normal transmission of the A change in the normal transmission of the electrical signal through the conduction electrical signal through the conduction systemsystem

Types of Atrioventricular Blocks Types of Atrioventricular Blocks

1st Degree AV Block1st Degree AV Block

2nd Degree AV Block, Type I2nd Degree AV Block, Type I

2nd Degree AV Block, Type II2nd Degree AV Block, Type II

3rd Degree AV Block3rd Degree AV Block

First degree heart blockFirst degree heart block

Signal originates in SA nodeSignal originates in SA node

Signal conducted to ventriclesSignal conducted to ventricles

BUT there is a delay in the conduction BUT there is a delay in the conduction pathwaypathway

1st Degree AV Block1st Degree AV Block

One P wave to each QRS complex One P wave to each QRS complex A constant PR intervalA constant PR interval PR interval of greater than >0.2 secsPR interval of greater than >0.2 secs bradycardia or tachycardiabradycardia or tachycardia

Etiology:Etiology: Prolonged conduction delay in the AV Prolonged conduction delay in the AV node or Bundle of Hisnode or Bundle of His

2nd degree heart block2nd degree heart block

Divided in to two types Divided in to two types Type 1 - Wenkeback (Mobitz type I)Type 1 - Wenkeback (Mobitz type I) Type 2 - Mobitz type IIType 2 - Mobitz type II

2nd Degree AV Block, Type I2nd Degree AV Block, Type I

PR interval progressively lengthensPR interval progressively lengthens One non conducted beat- One non conducted beat- (P wave not followed by (P wave not followed by

QRS).QRS). Following beat has shorter PR intervalFollowing beat has shorter PR interval

Etiology:Etiology: Each successive atrial impulse Each successive atrial impulse encounters a longer and longer delay in the AV encounters a longer and longer delay in the AV node until one impulse (usually the 3rd or 4th) node until one impulse (usually the 3rd or 4th) fails to make it through the AV node.fails to make it through the AV node.

Type II second degree blockType II second degree block

Type IIType II

Not as common as Type I and often leads Not as common as Type I and often leads to complete heart blockto complete heart block

Block usually within or below the bundle of Block usually within or below the bundle of HisHis

2nd Degree AV Block, Type II2nd Degree AV Block, Type II

Normal and constant PR interval in the Normal and constant PR interval in the conducted beats and not prolongedconducted beats and not prolonged

Dropped beatsDropped beats QRS complex may appear widenedQRS complex may appear widened Note : P wave may only show itself as a Note : P wave may only show itself as a

distortion of the T wavedistortion of the T wave 2:1 conduction -Two P waves per QRS 2:1 conduction -Two P waves per QRS

complexcomplex

2nd Degree AV Block, Type II2nd Degree AV Block, Type II

Etiology:Etiology: Conduction is all or nothing (no Conduction is all or nothing (no prolongation of PR interval); typically block prolongation of PR interval); typically block occurs in the Bundle of His.occurs in the Bundle of His.

3rd Degree AV Block3rd Degree AV Block

The P-P interval and R-R interval will be The P-P interval and R-R interval will be regular and consistent .Atria will beat at regular and consistent .Atria will beat at intrinsic rate (60-80).Ventricles (20-40)intrinsic rate (60-80).Ventricles (20-40)

No relation between P and QRS complexNo relation between P and QRS complex Note QRS may be abnormal shape (P Note QRS may be abnormal shape (P

wave and abnormal spread of wave and abnormal spread of depolarisation)depolarisation)

3rd Degree AV Block3rd Degree AV Block

Etiology:Etiology: There is complete block of conduction There is complete block of conduction in the AV junction, so the atria and ventricles in the AV junction, so the atria and ventricles form impulses independently of each other. form impulses independently of each other. Without impulses from the atria, the ventricles Without impulses from the atria, the ventricles own intrinsic pacemaker kicks in at around 30 - own intrinsic pacemaker kicks in at around 30 - 45 beats/minute.45 beats/minute.

• Most dangerousMost dangerous

Differentiating Atrioventricular Differentiating Atrioventricular BlockBlock

Examine Atrial rateExamine Atrial rate Examine ventricular rateExamine ventricular rate P wavesP waves PR intervalPR interval QRS complexQRS complex

RememberRemember

When an impulse originates in a ventricle, When an impulse originates in a ventricle, conduction through the ventricles will be conduction through the ventricles will be inefficient and the QRS will be wide and inefficient and the QRS will be wide and bizarre.bizarre.

Rhythm 1Rhythm 1

50 bpm• Rate?• Regularity? regularly irregular

nl, but 4th no QRS

0.08 s

• P waves?

• PR interval? lengthens• QRS duration?

Interpretation? 2nd Degree AV Block, Type I

Rhythm 2Rhythm 2

40 bpm• Rate?• Regularity? regular

nl, 2 of 3 no QRS

0.08 s

• P waves?

• PR interval? 0.14 s• QRS duration?

Interpretation? 2nd Degree AV Block, Type II

Rhythm 3Rhythm 3

60 bpm• Rate?• Regularity? regular

normal

0.08 s

• P waves?

• PR interval? 0.36 s• QRS duration?

Interpretation? 1st Degree AV Block

Rhythm 4Rhythm 4

40 bpm• Rate?• Regularity? regular

no relation to QRS

wide (> 0.12 s)

• P waves?

• PR interval? none• QRS duration?

Interpretation? 3rd Degree AV Block