Electrocardiography (ECG)

Definition:
The electrical activity of heart on a graph paper is called ECG.
How to study the ECG?
1-Heart rate
2-Rhythm
3-Axis
4-Chamber Hypertrophy
5-Infarction
6-Ischemia
7-P-R Interval
8-Block bundle branch or AV blocks
9-Q Wave
10-Q-T Interval

1-Heart Rate:
QRS complex occurring once per large square is occurring at the rate of 300/min.
QRS complex occurring once per small square is occurring at the rate of 1500/min.
Heart rate may be;
a- Regular
b- Irregular
a-Regular heart rate:
Same or equal distance/difference between R-R interval represents the regular heart rate.
How to calculate;
There are two methods to calculate the Sinus heart rate by;

1. By large boxes 
2. By small boxes 

1. By large boxes:
Account the large boxes between R-R interval e.g; 5 large boxes.
One large square heart rate at the rate of 300/min.
Use the formula;
300/large boxes=300/05=60 per min heart rate (HR).
2. By small boxes:
Account the small boxes between R-R interval e.g; 18 small boxes.
One small square heart rate at the rate of 1500/min.
Use the formula;
1500/small square=1500/18=83 per min HR.

*Here 60/min is normal/ Rough HR.
*And 83/min is sinus/ Accurate HR.

b- Irregular heart rate:
They have no Equidistant between R-R interval of whole ECG, represents the Irregular heart rate.
How to calculate;
There are two methods to calculate the irregular heart rate by;

1. QRS-complex take between 30 big boxes on regular ECG (Red in color) 
2. QRS-complex take between 06 sec strip to check HR (Green in color) 

1. QRS-complex take between 30 big boxes on regular ECG (Red in color):
Account 30 big boxes in an ECG starting from a QRS-complex.
Account the QRS-complex between the big 30 boxes e.g; 10 QRS-complex
Now use the formula;
QRS-complex X 10= 10 X 10= 100/min.

2. QRS-complex take between 06 sec strip to check HR (Green in color):
Account the 6 sec line on ECG paper starting from QRS-complex.
Account QRS-complex Between the 6 sec strip.
Now use the formula;
QRS-complex X 10= 6 X 10= 60/min.

* Here both methods are accurate.

2-Rhythm or Sinus Rhythm:
When the depolarization begins in the SA node of the heart, is said to be sinus Rhythm.
Arrhythmia:
When the depolarization begins in the other places of the heart like Atria and ventricular the Rhythm is named after the part of the heart where the depolarization sequence originate and an Arrhythmia is said to be present.
Sinus Arrhythmia:
Change in the HR associated with respiration, are normally seen in young peoples, and this is called Sinus arrhythmia.

* The rate of discharge of the SA node is influenced by he vagus nerves and reflexes originate in the lungs.

There are the six types of Rhythm:

• Normal sinus rhythm 
• Junctional rhythm 
• Atrial Fibrillation 
• Extra-systole 
• Supra-ventricular tachycardia 
• Ventricular tachycardia

Normal Sinus Rhythm:
It contains P wave, QRS-complex and T wave with same rhythm or rate.
Junctional Rhythm/Nodular:
If no P wave found its called Junctional rhythm, it is due to dysfunction of SA node and AV node that take part in depolarization.
Atrial Fibrillation:
Fibrillation in the right atrium due to not proper contraction of atrium is result of many P waves found like fibrillation of right atrium.
Extra-systole:
Other parts of the heart take part in depolarization like, Atrial muscles, Junctional region(AV Node) and ventricular muscles that show the ectopic beat and ectopic rhythm.

* Atrial ES have abnormal P wave shows AF.
* Junctional ES there is no P wave shows JR.
Supra-ventricular tachycardia:
There is QRS-complex and P & T waves emerge in each other.
Ventricular tachycardia:
It shows only QRS-complex No P waves and No T waves found.

3-Axis:
The average direction of the spread of depolarization wave through the ventricular as seen from the front is called "Cardiac Axis" Its useful to decide whether this axis can derived (direction) easily from the QRS-complex in lead I, II and III.

                         Lead AVF                                                       Lead I
QRS-complex    Upward                                                         Upward             (Normal)
                         Upward                                                         Downward       (Right axis)
                         Downward                                                    Upward            (Left axis)
                         Downward                                                    Downward       (Extreme right axis)

4-Chamber Hypertrophy:

There are four type of hypertrophy:

• Right Ventricular Hypertrophy
• Left Ventricular Hypertrophy
• Left Atrial Hypertrophy
• Right Atrial Hypertrophy

Right Ventricular Hypertrophy (RVH):

Right axis deviation on ECG.

Tall R wave in lead V1.

Deep S wave in lead V6.

* Sometime is said to be right bundle branch block (RBBB).

Left Ventricular Hypertrophy (LVH):

Tall R wave in lead V5 or V6 more than 25mm.

R wave in V5 or V6 plus S wave in lead V1 or V2 more than 35mm.

* Sometime is said to be Left bundle branch block (LBBB).

Left Atrial Hypertrophy (LAH):

P wave in duration more than 12 sec or 3 small square.

Its said to be P-mitral or left atrial enlargement (LAH).

Right Atrial Hypertrophy (RAH):

P wave in amplitude more than 0.3mv or 3 small square.

Its said to be P-pulmonary or right atrial enlargement (RAH).

5- Myocardial Infarction (MI):
Sequence of ECG changes:
Normal ECG__Raised ST segment__ Appearance of Q waves__Normalization of ST segment__Inversion of T waves.
Site of Infarction:
ECG findings on graph paper in different leads shows different diagnosis.

V1-V6                              Anterior wall MI
II,III & AVF                       Inferior wall MI
I, AVL, V5,V6                   Lateral wall MI
I, AVL                              High lateral wall MI
V5-V6                              Lower lateral wall MI
V1-V4                              Antroseptal wall MI

6-Ischemic Heart Disease (IHD):
Digoxin: ST segment slopes downward.
Ischemia: Flat ST segment depression.
T wave Inversion:

• Normal in leads III, AVR, V1, V2 & V3 in black peoples (Negro).
• Ventricular Rhythm.
• Bundle branch block.
• MI.
• RVH & LVH.
• WPW syndrome.

Site of Ischemia:


V1-V6                              Anterior wall Ischemia
II,III & AVF                       Inferior wall Ischemia
I, AVL, V5,V6                   Lateral wall Ischemia
I, AVL                              High lateral wall Ischemia
V5-V6                              Lower lateral wall Ischemia
V1-V4                              Antroseptal wall Ischemia

7-P-R Interval:
(AV delay)
Current or impulse stops at this point.
Normal: 0.12 sec- 0.2 sec i.e; 3 to 5 small square or 120ms to 200ms.
Prolonged: If P-R interval more than 5 small square, then AV node delay increases and called AV block and heart block.

8-Block bundle branch or AV blocks:
There are three types of heart block;

I degree AV block
II degree AV block

• Mobitz type I
• Mobitz type II

III degree AV block

I degree AV block:
P-R interval fix prolonged e.g; 7 small square.
No beat drops i.e; no drops of QRS-complex.
No any pathology rather than it.
Its called 1 degree of heart block.

II degree AV block:
There are two type of it;
Mobitz type I
Mobitz type II

• Mobitz type I:

P-R interval progressively prolonged e.g; more than 5,6,7,8 and so on.
Beat drops i.e; drops QRS-complex.
Pulse is irregular clinically.
Its also known is Wenchebach's phenomenon.

• Mobitz type II:

P-R interval fix prolonged e.g; 7 small square.
Beat drops i.e; drops QRS-complex, e.g; more P waves than QRS-complex.
Its not due to lengthening of AV conduction time, its usually due to block within bundle of His.
Its mostly due to organic heart disease.
Its lead to complete heart block.

III degree AV block:
Its also known as complete heart block, i.e; no impulse from atria to ventricular reaches.
Its only maintained by escape Rhythm, i.e; arising from bundle of His (narrow QRS-complex at the rate of 50 to 60 bpm),  Below the bundle of His (make broad complexes at the rate of 15 to 40 bpm)
Exertion or Exercise does not increase the heart rate.

9-Q Wave:
-Small septal Q wave are normal in lead I, AVL and V6.
-Its can also seen in lead III but in AVF is not a normal variant.
-Probably indicates infarction, If MI present in more than one lead i.e; more than 2 or more leads, longer than 40 ms in duration and deeper than 2 mm in amplitude.
-Q wave in lead III (but not in AVF) pulse Right axis deviation may indicates "Pulmonary embolism".
-Leads showing Q waves indicates the site of infarction.
i.e;

V1-V6                              Anterior wall Old MI
II,III & AVF                       Inferior wall Old MI
I, AVL, V5,V6                   Lateral wall Old MI
I, AVL                              High lateral wall Old MI
V5-V6                              Lower lateral wall Old MI
V1-V4                              Antroseptal wall Old MI

10-Q-T Interval: