ECG

Electrocardiogram (ECG)

Mohammed Hashim Almosawy
Thi-Qar Medical College

ECG:

Is a recording of electrical waves that produced by the electrical activity of the heart , it is one of the most valuable diagnostic tools in modern medicine .

It is essential for diagnosis of cardiac problems if any changes in cardiac activity are developed

Basic components of the healthy heart beat

ECG paper

- One large box = 5 small boxes
- One small box = o.o4 sec
- One large box = 0.2 sec


* Each 5 large boxes = 1 second

Basic components of the healthy heart beat

1- ECG waves

P : atrial depolarization (contraction)

QRS : ventricular depolarization (contraction)
T : ventricular repolarization (relaxation)
U : purkinje fibers repolarization

2- Segments

isoelectric lines because these is no electrical activity during this time
* Two segments:
1- P-R segment : ( starts from the end
Of the P wave to the beginning of the Q wave )


2- S-T segment : ( starts from the end of
S wave to the beginning of T wave )
Normal duration of S-T segment = 0.08 – 0.12
= 2 – 3 small boxes

3- Intervals :

* 3 Intervals:
1- P-R interval : ( from the beginning of P
wave to the beginning of Q wave )
Normally : 3-5 small boxes

2- Q-T interval : ( from the beginning

of Q wave to the end of T wave )
Normally : 8 to 12 small boxes
3- R-R interval : ( from R wave to next
R wave )




How to read ecg to approach to the dx ?
The following are very important parts in ECG that help you to reach the diagnosis
1- Rate : normal HR is 60 – 100 beat /min
A – if the heart rhythm is regular so I calculate the large boxes between R wave and next R wave and dividing 300 on it .
Example: number of large boxes between adjacent R waves = 4 large boxes so
the heart rate =300/4 = 75 beat / min
B- if the rhythm irregular so I calculate the number of QRS complex in 30 large boxes then multiply by 10 .
Example: number of QRS complex in 30 large boxes = 8 QRS complexes so
the heart rate = 8 * 10 = 80 beat /min

Normal heart rate

Bradycardia :

Regular rhythm tachycardia

2 – Rhythm :

regular or irregular and if the P wave present or not .
If the P wave present so it is sinus rhythm , if not present it is not sinus rhythm
* To know the rhythm you carefully compare each R-R intervals, if all the R-R intervals
are equal so it is regular rhythm , if not equal so it is irregular rhythm .
Example: regular sinus rhythm

Irregular sinus rhythm

(Narrow R-R interval) (wide R-R interval)
If the P wave can not determined so it is not sinus

3- Morphology of P wave and QRS complex and their relationship

- normal shape of P wave or not ( normally the P wave identical in shape and up right )
Normal shape of QRS complex , width ( normal or broad )
If the P wave followed by QRS or not


(This P wave not followed by QRS)

4- Axis

To know the axis is normal or not look to lead 1 and lead aVF

1- Normal axis : positive QRS in lead 1 and aVF

2- Right axis deviation : negative QRS in lead 1 and positive in lead aVF
3- Left axis deviation : positive QRS in lead 1and negative in lead aVF

* Normal axis

* Right axis deviation

Left axis deviation

5- intervals

1- P-R interval ( normally 3-5 small boxes )
2- Q-T interval ( normally 8 – 12 small boxes )

this ECG of WPWS

Short P-R interval

Long Q-T interval

6- Segments

1- P-R segment
P-R depression: this is a characteristic of pericarditis

2- S-T segment :

A- S-T elevation : we consider the S-T elevated if ;
-elevation more than one small box in all the leads 
- elevation more than two small boxes in two contiguous leads
like ( V1 and V2 or V3 and V4)

S-T elevation in V2 and V3 ( anteroseptal M I )

B- S-T depression ; we consider the S-T depressed if ;

- depression more than 0.5 small box
- the depression should be in at least two contiguous leads

7- T wave :

shape and amplitude
A- T wave inversions : can be caused by acute coronary ischemia( acute MI) , hypertrophic cardiomyopathy

B- Tall tented T wave : hyperkalaemia

12 leads of ECG

1 – 3 limb leads :
( I , II , III )
2- 3 augmented leads :
( a V R , a V L , a V F )
3 – 6 precordial leads :
( V1 , V2 ,V3 ,V4 ,V5 , V6 )


* Each lead represent a specific area in the heart

leads presentation on ECG

- Leads represent the lateral side of the heart : I , a V L , V5 ,V6
- Leads represent the inferior side : II , III , a V F
- Leads represent the septum of the heart : V1 , V2
- Leads represent the anterior of the heart : V3 , V4

Cardiac Arrhythmias

* Remember that for interpretation of ECG we should know the following :
1- rate
2- rhythm
3 -Morphology of P wave and QRS complex and their relationship
4- T wave
5- intervals
6- segments
7- axis


NOTE : BROAD QRS complex when the width of QRS more than 3 small boxes .

1- Sinus tachycardia :

- Sinus rhythm where the heart rate is faster than the normal range

-ecg paper shows ( Narrow complex tachycardia , Regular rhythm , p wave normal , ….)

* Causes : ( anxiety , pain , fever , dehydration , hypovolemia , anaemia , infection , drugs such as dopamine ,…….)

2- Sinus bradycardia

Is a sinus rhythm where the heart rate is slower than the normal range .

- ECG paper shows ( narrow complex bradycardia , regular rhythm , P wave normal , …)

* Causes: ( hypothermia , hypoxia , hyperkalaemia , athletes , drugs such as digitalis and beta blocker , …..)

3- Premature atrial contraction ( atrial ectopic beat )

the electrical activity originate in the atrium other than the sinoatrial node , resulting in atrial arrhythmias that characterized by unusual P wave shape.

ECG finding :

- P wave come prematurely
Before the next expected beat
- Unusual P wave shape
Normal QRS
Irregular rhythm

* Causes : ( electrolyte imbalance , cardiac stimulant such as tobacco , caffeine and alcohol , IHD , COPD )

4 – Supraventricular Tachycardia

There is an extra pathway that the electrical impulse follows , which causes a fast heart rate .
* causes : ( any cardiac surgery that could cause inflammation in the atria or ventricles , sinus arrhythmia , atrial flutter )




ECG findings :
Narrow complex tachycardia
regular rhythm 
No P wave 
Some S-T segment depression 
Dx : Supra- ventricular tachycardia

* Other Ecg example :

5 – atrial fibrillation ( AF )

Prevalence of AF increase with age : 5% of individuals above 70 years , 10 % of individuals above 80 years
15-25 % of all ischemic strokes are associated with AF
* Causes of AF :
- valvular heart diseases
- ischemic heart disease
- thyrotoxicosis
- pulmonary disease


both A and B ECG paper are example on AF
A –

B -

both above ECG findings show :

1- narrow QRS complex ( normal width ) tachycardia
2 – irregular - irregular rhythm
3- no P wave 

Dx : Atrial fibrillation with rapid ventricular response ( tachycardia )

Note: not always the AF associated with rapid ventricular response but sometimes associated with normal ventricular response ( normal rate ) or with slow ventricular response ( bradycardia )

6- atrial flutter

Less common than AF
Characterized by zigzagging baseline ( saw tooth waves ) best seen in in leads II , III , a V F
* CAUSES ;
- Associated with significant cardiac disease such as mitral valve disease
- complicate 5 % of acute M I
- Flutter usually arise in the Rh atrium and often associated with diseases of right side of the heart : e.g. chronic obstructive pulmonary disease ( COPD) , pulmonary embolism and chronic congestive heart failure

Finding :

Narrow QRS complex tachycardia
Regular rhythm 
Flutter zigzagging waves ( saw tooth pattern ) 
DX: atrial flutter

7- multi-focal atrial tachycardia

Causes: ( lung disorders , IHD , low blood pressure , hypomagnesaemia )

* ECG

Findings:

1- narrow complex tachycardia
2- irregularity
3- different morphologies of P wave at least 3 P waves morphologies in the
same lead ( important point)


8- Ventricular Tachycardia

Two types :

1-sustained lasts for more than 30 seconds
2-non-sustained lasts for less than 30 seconds .
VT is a serious cardiac arrhythmia , in some patients cardiac output will be lost .
Causes : ( IHD , MI , cardiomyopathy , electrolyte imbalance )

VT differ from supraventricular tachycardia arrhythmias ( SVT , A Flutter , A Fibrillation )
because the origin of beat from the ventricles so result in broad QRS complex

Look to this ECG

The above ECG show :

1- broad complex tachycardia
2- regular
3- QRS complexes have the same morphology
Dx : VT


Note : other findings that can be seen in VT ecg are :
a- P wave may be present or not
b- fusion beats and capture beats

Read in details about capture

and fusion beats(mechanism) in any
book of ECG

9- Torsade de pointes

Polymorphic ventricular tachycardia with irregularity .
Causes: ( anti-arrhythmic drugs , electrolyte imbalance e.g. hypokalaemia and
hypomagnesaemia )

* spiky QRS complexes rotating irregularly

around the isoelectric line at rate about
200 beat / min







Ecg

*Findings:

1-broad complex tachycardia
2- irregular rhythm
3-prolongation of Q-T interval
4 – twisting of points

10- Ventricular fibrillation

very bizarre irregular ECG , random in both amplitude and frequency
Causes: ( IHD , Heart failure , electrolyte imbalance , cardiomyopathy )
-ECG :

Finding :

1- bizarre shape
2- broad complex tachycardia with different size
3- irregular with no identifiable P wave

Dx: Ventricular fibrillation

Av block

1 – first degree AV block

there is a delay in the conduction of atrial impulses to the ventricles .

It is usually benign

If associated with acute MI , close monitoring of the ECG is required because may progress to
higher degree of AV block
Causes : ( inferior MI , IHD , electrolyte imbalance , drugs such as beta- blocker)

ECG:

Findings:
1- normal rate
2- sinus regular rhythm ( normal P wave , normal R-R interval)
3-prolongation of P-R interval more than 5 small boxes ( constant P-R prolongation)
Dx: first degree AV block

2- Second degree AV block ( mobitz I OR Wenckebach)

Causes : ( inferior MI , electrolyte imbalance , drugs such as beta blocker , digoxin , verapamil )
* ECG

Findings:

1- normal rate
2- irregular
3- progressive prolongation of P-R interval with dropped QRS ( dropped beat )
Dx : second degree AV block

Progressive

Prolongation of P-R

Dropped beat

3- Second degree AV block ( Mobitz II )

- It is less common than second degree type I , it is more serious than type I , it can suddenly progress to third degree ( complete block ) .
Causes: ( acute MI , drugs such as digoxin , beta blocker , verapamil )
ECG:

Findings:

1-normal rate
2- irregular rhythm w
3- dropped QRS complexes
4- prolongation of P-R interval but constant
Note : the only difference between type I and type II prolonged P-R intervals in type I are progressive while in type II are constant .

Dx : second degree AV block type II

4- Third degree AV block ( complete )
Total failure of conduction between the atria and the ventricles .
Characterized by AV dissociation so the P wave totally not related to the QRS complexes
Causes : ( septal acute MI with extensive necrosis of the septum , fibrosis of bundle of his ,
endocarditis , drugs )
* ECG :

Findings :

1- bradycardia
2- more P waves than QRS complexes
3- complete dissociation between P wave and QRS complex

Dx: third degree heart block ( complete )

5 – Right bundle branch block ( RBBB)
Conduction down the right bundle branch is blocked
Causes : ( ischemic heart disease including right bundle branch , pulmonary embolism , cardiomyopathy , rheumatic heart disease )
* Diagnosis made by examining the chest leads V1 and V6 .
* ECG findings in RBBB :
- normally in ECG after P wave there is negative ( Q wave – positive R wave – negative S wave ) , in RBBB in V1 after the P wave there is ( positive r wave – negative S wave – positive R wave )
So this give r S R pattern in V1 ( M- shape QRS complex in V1 )
Broad complex ( more than 3 small boxes )
In lateral leads ( I , a V L , V5 ,V6 ) there is ( negative Q , positive R wave , negative wide slurred S wave ) so this give shape of ( W shape in these leads )



M and W shapes in ECG

ECG:

Findings:
1- r S R pattern in V1 , V2 , V3 with broad complex
2- wide , slurred S wave in leads V6, V5, I , a V L
Dx : right bundle branch block

6 – left bundle branch block

Conduction down the left bundle branch is block
Causes : ( ischemic heart disease including left bundle branch , cardiomyopathy , hypertensive disease )
Diagnosis made by examining the chest leads V1 and V6 .
ECG findings in LBBB:
-broad complex
r S pattern in V1 with dominant S wave pattern or Q S pattern give the W shape complex
Complex in lateral leads ( I , a V L , V5 ,V6 ) gives either M shape ,R S pattern , monophasic shape , notched shape )


Complex patterns in lateral leads :

ECG:

Findings :
1- broad complex
2- q S pattern in V1 ,V2 ,V3 with dominant S wave
3- M shaped pattern in ( I , a V L , V6)

Other ECG :

Findings:
1- broad complex
2- r S pattern in V1,V2,V3 with dominant S wave
3- notched complex in ( I , V5 , V6 ) , M shaped in a V L ,

Myocardial infraction

Remember the leads presentation

A ) S-T elevation MI

Elevation should be more than one small square in all the leads OR more than 2 small squares in two contiguous leads that represent the same area of the heart .
Example ECG

Findings: 1- S-T elevation in V1,V2,V3 and V4

DX: anteroseptal myocardial infraction

Other ECG:

Findings:
1- S-T elevation in V2,V3,V4
2- other important and clear finding (homework )

B) Non- S T elevation MI (either S-T depression MI or T wave inversion MI )

*S-T depression should be more than 0.5 small square and the depression should be in at least two contiguous leads .
Example ECG:

Findings : ( S-T depression in V2,3,4,5,6 , I , II , a V L )

- Other important and clear findings .( homework )

OTHER Example ECG for non STEMI

Findings:
1- inferior leads S-T depression (II ,III , a V F )
2- S-T depression in leads ( V3,V4,V5)

hyperkalemia

Ecg changes :

Example ECG :

Findings :
1- peaked , tented T wave in V2, V3 ,V4, V5
2- Broad complex with changes of left bundle branch block
*( Management of hyperkalemia is very important )

Pericarditis

ECG :

Findings:

1- P-R segment depression in multiple leads ( specific ECG marker for pericarditis )
2 – saddle shape S-T elevation also in multiple leads

Other ECG example :

Findings: 1- P-R segment depression
2- saddle shape S-T elevation

Wolf Parkinson white syndrome

WPWS is a condition where atrial impulses bypass the AV junction and activate the ventricular myocardium directly via an accessory pathway ( bundle of Kent ) .
Thought to be hereditary
Its incidence is 0.1-0.3 % of population

1) WPWS type 1:

Left sided pathway resulting in predominant R wave
ECG example :

Findings in above ECG :

1- Sinus rhythm
2- broad QRS complexes with slurred upstroke ( delta wave ) associated with
dominant R wave in V1
3- very short P-R interval ( important finding in WPWS )
3- right axis deviation

2) WPWS type B

RIGHT sided pathway resulting in predominant S or QS wave
- The ECG findings the Same as in type A but instead of dominant R wave in type A there is dominant S wave or QS pattern in V1 .

Ventricular hypertrophy

1– Left ventricular hypertrophy
* Sokolov – Lyon criteria , voltage criteria
= most deepest S wave in V1 or V2 + tallest R wave height in V5 or V6 > 35 mm ( > 7 large boxes)
( more accurate criteria )
other criteria is ( a V L criteria )
R wave in a V L > 12 mm
Causes :( systemic
hypertension , aortic
regurgitation , other )

ECG of LVH

Look to the depth of S wave in V1 and tall of R wave in V6 so the sum of both > 35 mm
 Note : in LVH the R wave amplitude will progressively increase from V1 to V6 ( gradual increase ) while the S wave depth will progressively decrease .

2- Right ventricular hypertrophy

here the R wave amplitude progressively decrease in length from V1 to V6 while the S wave
depth will progressively increase from V1 to V6 ( diagnosed by The same criteria ) .

Good luck