ECG5

16/12/2008 ECG Diag 5 /ghazi

Principles of ECG Diagnosis5

Conduction Disturbances

Dr Ghazi Ahmad RadaidehMD, FRCP

Rashid HospitalDubai - UAE


Conduction Disturbances

1.Sino-Atr ial Exit Block2. Atr io-Ventr icular (AV) Block

1st Degree AV Block Type I (Wenckebach) 2nd

Degree AV Block Type II (Mobitz) 2nd Degree

AV Block Complete (3rd Degree) AV

Block AV Dissociation

3.Intraventr icular Blocks RBBB LBBB Left Anterior Fascicular

Block Left Posterior Fascicular

Block Bifascicular Blocks Nonspecific Intraventricular

Block Wolff-Parkinson-White

Preexcitation

Objectives


Reading 12-Lead ECG step-by-step (RAWIHI)

1. Rate, Rhythm and Regular ity2. Determine the QRS Axis3. Evaluate the Waves (P,QRS,T ),

Intervals (PR,ST,QT)4. Evaluate for chamber Hyper trophy5. Look for myocardial Infarction and Ischemia6. Interpret the ECG


Delays Delays are caused by a degeneration

within the sinus node, which are characterised by long intervals between consecutive atrial depolarisations.

The causes and types of delays are:Dropped Beats & Sinus Block

Sinus Pause

Sinus Arrest

Escape Beats


Type II sinoatrial exit block. (Dropped Beat)

delay is a multiple of the basic sinus intervalPP intervals fairly constant until conduction failure occurs.


Sinus Pause

delay of activation within the atria for a period between 1.7 - 3 seconds.


Sinus Arrest

Failure of sinus node discharge (pause)

Absence of atr ial depolar ization

Per iods of asystole

delay of activation within the atria for a period equal to, or greater than, 3 seconds


Atrioventricular Block2. Atr io-Ventr icular (AV) Block

1st Degree AV Block

Type I (Wenckebach) 2nd Degree AV Block

Type II (Mobitz) 2nd Degree AV Block

Complete (3rd Degree) AV Block


1st Degree AV Block

60 bpm Rate? Regularity? regular

normal

0.08 s

P waves?

PR interval? 0.36 s QRS duration?


1st Degree AV Block


2nd Degree AV Block, Type I

50 bpm Rate? Regularity? regularly irregular

N, but 4th no QRS

0.08 s

P waves?

PR interval? lengthens QRS duration?


2nd Degree AV Block, Type I I


nl, 2 of 3 no QRS

0.08 s

P waves?

PR interval? 0.14 s QRS duration?


Mobitz type II block


Complete (3rd Degree) AV BlockNo impulse conduction from the atria to the ventricles

Narrow QRS complexescape rhythm

When the conduction starts within or close to, the AV node

Wide QRS complexescape rhythm

When the conduction is of ventricular origin( below AV node)


3rd Degree AV Block


no relation to QRS

wide (> 0.12 s)

P waves?

PR interval? none QRS duration?


Complete (3rd Degree) AV Block


Is it important to know the site of AV Block?

if the problem is located in the AV node, pacing is usually not indicated,

if distal to the AV node, in His or the bundle branch system, a pacemaker is indicated. There are simple, noninvasive measures to

make that distinction.


Diagnostic cr iter ia for RBBB QRS duration = >0.12s in Complete"

RBBB and 0.1-012 in incomplete RBBB.

Wide slur red R wave in leads V1, V2 (V3) + secondary R wave (R) (rSR or rsR )

Wide slur red S wave in leads I, V5, and V6

Associated feature ST segment depression and T wave

inversion in V1, V2 (V3)


Right bundle branch block


Conditions associated with RBBB

Rheumatic heart disease Cor pulmonale/right ventricular hypertrophy Myocarditis or cardiomyopathy Ischaemic heart disease Degenerative disease of the conduction system Pulmonary embolus Congenital heart disease for example, in atrial

septal defects Normal finding( No organic heart disease)


Diagnostic cr iter ia for LBBB QRS duration = >0.12s QRS complexes wide or slurred and

upright in leads 1, V5, and V6 No q waves in I, V5 and V6 leads. A predominantly negativeQRS

complex in lead V1. Associated features

St depression and T wave inversion in I, V5-6

Poor R wave progression in the chest leads

Left axis deviation common but not invariable finding

V1

V6

Lead I


Left Bundle Branch Block


Nonspecific Intraventricular Conduction Defects (IVCD)

Causes of nonspecific IVCD include: Ventricular hypertrophy (especially LVH) Myocardial infarction (so called perinfarction blocks) Drugs, especially class IA and IC antiarrhythmics Hyperkalemia

Pacemaker beat

QRS duration >0.10s indicating slowed conduction in the ventricles

Criteria for specific BB or fascicular blocks not met in all 3 of the KEY leads (i.e., leads I and V1 and lead V6


Left anter ior hemiblockcharacterisedby abnormal left axis deviation) in the absence of an inferior myocardial infarction or other cause of left axis deviation.

0o

30o

-30o

60o

-60o-90o

-120o

90o120o

150o

180o

-150o

I

II


Left Anterior Fascicular Block (LAFB)...

the most common intraventricular conduction defect Left axis deviation, usually -45 to -90 degrees rS complexes in leads II, III, aVF Small q-wave in leads I and/or aVL QRS duration usually


(LAFB)...


Left Posterior Fascicular Block (LPFB)....

Left poster ior hemiblock is characterised by: Right axis deviation (usually > +100 degrees)

0o

30o

-30o

60o

-60o-90o

-120o

90o120o

150o

180o

-150o

I

II


Bifascicular Block

Bifascicular block is when 2 of the conduction system pathways below the AV node are blocked. They are defined as one of the following:

1.RBBB and left anterior hemiblock

2.RBBB and left posterior hemiblock3.Complete LBBB (both left anterior and left posterior)


Bifascicular :RBBB + LAFB


Wolff-Parkinson-White PreexcitationECG cr iter ia :

1.Shor t PR interval (0.10s)

Secondary ST-T changes due to the altered ventricular activation sequence


Pacemakers

The spikebefore the QRS represents the firing of the pacemaker

A pacemaker is a device that stimulates the ventricles to fire. An electrical energy or impulse is delivered and the ventricles respond depolarizing and creating cardiac output.


AAI mode


Regular and wide QRS complexes with each QRS complex preceded by a deep and narrow spike.

VVI mode


AV Sequential Pacing DDD


CRT

3 pacemaker leads:

To RVA To LV

through cardiac veins

To RAA


Biventricular pacing

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