ECG EDUCATION--D

THE 12 LEAD ECG MACHINE

In the market ECG machines are available in various types such as 12-lead,6-lead,3-lead, and single lead types.

When we think to buy one for our home use we must first familiar with these types.

For example when we buy a 12-lead machine we should have a thorough knowledge regarding the number of electrodes (Leads) and what are the functions of each electrode and how they should be placed on our body.

See the following animated diagram for a 12-lead ECG machine:-            

                             

Fig-1

In Fig-1 we can see the various electrodes and how they are placed on a human body and brief details are given below:-

1.aVR-Lead:-This lead has been attached at the wrist below the palm at the right hand.

2.aVL-Lead:-This lead has been attached on the left-hand wrist similarly.

3.aVF(R)-Lead:-This lead has been attached at the right foot which you can see as a red dot at the right foot without naming as it serves merely as an earth connection without any further involvement in the ECG procedure.

4.aVF-Lead:-This is attached on the left foot similar to the right.

The above mentioned three unipolar leads namely aVR,aVL, and aVF are forming a triangle known as Einthoven's Triangle.

The above-mentioned triangle is shown with green lines in the above figure.

The triangle is very important as it adds three more virtual bipolar electrodes namely lead-I,

lead-II, and lead-III (Limb bipolar electrodes)

5. In the above diagram (Fig-1) the lead-I receives electrical signals from aVR, and aVL and sends it to the heart.

6. Similarly, the lead-II receives signals from the two unipolar leads namely aVR and aVF and send to the heart

7. The last bipolar lead receives signals from aVL and aVF and sends it to the heart.

Now we attached 7 electrodes out of which one is earth (aVR-F) and the three bipolar electrodes are virtual and embedded in each side of the triangle.

Now we have to place six more electrodes known as chest electrodes as per the methods given below:-
V1-electrode:4th intercostal space at the right sternal border. This means from the first rib next to the shoulder bone (clavicle) below the neck to the space between 4th and 5th ribs and right to the chest big bone(sternum)
V2-electrode:-Similar to the above lead but to the right of the sternum.
V3-electrode:-Midway between V2 and V4.
V4-electrode:-5th intercostal space at the midclavicular line
V5-electrode:-Left anterior axillary line horizontally next to V4.
V6-electrode:-Left midaxillary line on the same horizontal pane next to V4 and V5.
Now the views of the heart by the electrodes are diagrammatical as follows:-

                                 Fig-2 In the above diagram (Fig-2) there are three views such as from the anterior(upper), posterior(lower), and lateral(side) views.
aVR, I,aVL, V1, V2, V3 are viewing the heart from the upper side.
aVF is viewing the heart from the lower side
II, III, V4'V5'and V6 are viewing from the lateral sides.
Terminology:-
Electrodes-----Electrical conductor or receiver
Lead         ---- The electrical potential difference                              between two electrodes
aVR------Augmented Voltage Right

aVL ------Augmented Voltage Left
aVF ------Augmented Voltage Foot

Note:-Many times these two terms 'lead and electrode' are used interchangeably and it doesn't matter.
The bipolar electrodes are virtual and hence they are leads only.

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                                                           Continued in the next post (E)...

ECG EDUCATION-C-ECG AXIS

AXIS OF HEART ON ECG

The axis of the heart in the ECG is the main direction of the overall electrical conductions of the heart. It is very easy to assess the QRS axis which is the electrical depolarization of the ventricles. Since the total mass of the ventricles represents 90% of the total mass of the heart assessing the QRS axis can give us the knowledge of almost all of the heart problems. The QRS axis can be easily observed at the lead-II column because the lead II is fixed very near to the ventricles. This column is separately mentioned at the bottom as the last column in the ECG paper
P-axis may give us some figures for the problems in the atrium only which is 1/8 that of the heart problems.
Hence we are going to concentrate more on the QRS axis in the following article.

Normally all the electrical activities of the heart are directed towards -30 degrees to +90 degrees in a quadrant as shown in the diagram below:-

Fig-1

In the above diagram (Fig-1) the circle has been divided with two crossed pairs of diameters perpendicular to each other to form 4 main quadrants.
For the illustrative purposes these 4 quadrants have been subdivided into sub-quadrants with 30 degrees radians each.
In Fig-1 if the axis (Yellow) is shifted to the left (-30 to -90) then it is known as Left Access Deviation (LAD) which indicates that there are problems in the left ventricle such as hypertrophy or a fascicular block.
Similarly if the axis is shifted to the right side then it is known as Right Access Deviation (RAD) which indicates there are problems in the right ventricle.
Normal ECG:- In the above circle (Fig-1) the leads I, II, and aVF lie in the normal yellow region. Hence in the ECG graph if the QRS complex is positive in the lead-I and II column and aVF column then we can confirm that the ECG is normal with normal ventricular depolarization and the axis of the electrical activities are normal.
Abnormalities:- In the above circle aVL lies on the quadrant between -30 to -90 degrees.
Hence in the ECG columns of lead-I and aVL shows positive QRS and column aVF shows negative QRS then there is LAD which indicates there are problems in the left ventricle.
Similarly if column I shows negative QRS, and the columns of aVF and the III-lead shows positive QRS then there is RAD.
If both column I and aVF shows negative QRS then there is an indeterminate axis which means extreme deviation. 

How to be Familiar With ECG Columns

                             

Fig-2

See the above graph. When you have received your ECG report you may notice on your ECG graph which will look like the one shown above. (Fig-2)
Descriptions as follows:-
1)I-column:-This shows the deflection QRS by the I-bipolar electrode or lead
2)II-column:-This shows the QRS axis deflected in the II-bipolar electrode or lead
3)III-column:- This shows the QRS-axis deflected in the III-bipolar electrode or lead.
4)aVR column:-This shows the QRS deflection at the aVR-unipolar lead.
5)aVL-column:-This shows the QRS axis deflected at the aVL-unipolar lead.
6)aVF-column:-This shows the QRS axis deflected at the aVF-unipolar lead
7)V-1 column: This shows the QRS deflection at the 1st chest lead
8)V-2-column:- This shows the QRS deflection at the 2nd chest lead.
9)V-3-column:-This shows the QRS deflection at the 3rd chest lead.
10) V-4-column:-This shows the QRS deflection at the 4th chest lead.

11)V-5-column:-This shows the QRS deflection at the 5th chest lead.
12)V-6-column:-This shows the QRS deflection at the 6th chest column.

                                                Continued next...

ECG ABNORMALITIES-ECG EDUCATION-B

ECG ABNORMALITIES

Before we go into the subject we must observe some parameters in the ECG.

AXIS OF THE ECG

The axis of the ECG is the major direction of the overall electrical conductions of the heart.

This we can see in the next post in detail.

First of all we must know about the columns in the ECG.

There are 12 columns in your ECG chart. Ignore the first three columns namely 1) aVR- V1- V4; 2)aVL- V2- V5; 3)aVF- V3- V6.

Note the last column which is Sinus Rhythm or Lead II- column. 

In this column you can observe three things namely normal sinus rhythm, sinus bradycardia, and sinus tachycardia. Any of the last two if present then your ECG is abnormal.

Fig-1

1. Normal Sinus Rhythm:-(See Fig-1)

In this the heart rate is normal (60 to 100 bpm), all R-R intervals are equal in length.

The P- wave appear normal (not over 2.5 mm or 2.5 ss)in height, and (not more than 0.12 sec or 3ss) in width. The P-wave represents the two upper chambers (Atria) contraction (Atrial Depolarization)
The QRS complex which represents the contraction of the lower chambers (Ventricular Depolarization)

The P-R interval is the length at the beginning of the upslope of the P-wave to the beginning of the QRS complex and normally it must be 0.12 to 0.20 seconds or 3 to 5 ss.

The normal duration of the QRS complex must be between 0.08 to 0.1 sec or 2 to 2.5 ss.

The amplitude of the R-wave in the sinus rhythm-II column should not be more than 20mm or less than 4 LS.
The QT interval(From the beginning of the Q-wave to the apex of the T-wave should not be more than 2 large boxes or 0.4 sec.
The ST interval fits and overlaps over the isoelectric line and its length is not over 0.08 sec or 2ss.

2. Sinus Bradycardia:-(See Fig-1)
    This can be identified from the ECG by calculating the HR which is <50 BPM.
The RR intervals are elongated
If still the waves are regular then it may not be worried and it may be temporary conditions due to lack of body movements.

3. Sinus Tachycardia:-(See Fig-1)
    This can be identified by calculating the HR which is above 130 BPM. Again if the waves are regular then this too not to be worried as it may be due to over activities such as sports, exercises or work overloads

PATHOLOGICAL OR ABNORMAL ECG 

Fig-2

1.Atrial Fibrillation(See Fig-2)

Examine the P-wave and the PR interval

In atrial fibrillation the P wave is almost absent or invisible and the QRS complexes are irregular as shown in the diagram above. (Fig-2)
Clinical Symptoms of A-fib:-
1.Palpitations with feelings of difficulties with racing flip-flap speed of the heartbeat.
2.Tiredness and weakness
3.Headache
4.Breath short
5.Chest tightness and pain
Atrial fibrillation also occurs if there is Sinoatrial Exit Block means the conduction is blocked and cannot exit out of SA node. A prolonged SA node exit block (III degree block) can cause cardiac arrest.
Some times or infrequently if there is a negative U-shape deflection that immediately follows the T-wave and if it is prominent then it means there is suspected hypokalemia (low potassium), or hypercalcemia(high calcium) or hyperthyroidism.
2. Atrial Flutter:-(See Fig-2)
In Atrial flutter the ECG shows many P-waves as in the diagram.
In atrial flutter the atrium is stimulated irregularly by the SA node.
Clinical symptoms of A-Flutter:-
Very similar to A-fib with less severity.
3.AV CONDUCTION BLOCK
There are three degrees of AV conduction blocks.
The symptoms are as follows:-
1. The heart rate slows down
2. Some times it may not be worried but many times it may be fatal.
3. In the ECG the P-R intervals are elongated to such a limit after which the P-wave and R-waves have no connections at all and the condition is the third-degree AV block.
4.Irregular Heartbeats
5.Syncope and dizziness
6.Chest pain.

Fig-3

4. Ventricular Tachycardia:-(See Fig-3)

Ventricular Tachycardia is the fast heart rhythm with ventricles contracting and relaxing very fast and equal to exceed 100 bpm. Because of ventricles' fast actions the atrial actions are masked and hence there are no visible P-waves. The heartbeat is so fast so that it has fewer chances to be filled with blood.
In VT randomly any two or three beats may be normal with clear P and T waves.
Symptoms of V.T:-
1.Neck tightening
2.Palpitations
3.Nausea and vomiting
4.Headache
6.Dizziness
5. Ventricular Fibrillation:-(See Fig-3)
Ventricular fibrillation is very similar to ventricular tachycardia but more serious than VT because in V.F the ventricles beat irregularly and faster than in VT and incoordinate to fill in and pump out the blood.VF if not treated immediately may lead to cardiac arrest and death.
Symptoms vary similar to VT.
6.Atrial Enlargements:-(See Fig-3)
From the ECG the appearance of the P-wave will indicate the presence of enlargements on either or both the atria. (see the diagram above)
The cone-shaped P-wave apex may indicate there is an enlargement in the right upper chamber (right atrium) 
Causes and symptoms:-
1. The tricuspid valve which is in between the right atrium and ventricle may be damaged.
2.Due to right ventricular failure.
3.Pulmonary hypertension -High pressure in the pulmonary artery.
4.Breathing difficulties
5.Palpitations
6.Arrhythmias
The M-shaped P-wave apex is the indicator of left atrial enlargement 
Causes and Symptoms:-
1.Due to the mitral valve regurgitation, stenosis, and damage
2.Left ventricle failure
3.High B.P
4.Atrial fibrillation
5.Heart failure
6.Fluid build-up and weight gain
7.Breathing difficulties
8.Palpitations.
7.Myocardial Infarction (Heart Attack)(Fig-3)
The ECG changes are as follows:-
1.T-waves are elevated (Hyperacute T-waves)
2.Elevated ST intervals
3.Followed by negative T-wave deflection
4. Finally negative large deflection of Q-wave occurs.
Ischemia develops due to a block of blood circulation and oxygen supply to a portion of the heart muscles. If this ischemia is mild and reversible the can recover its coronary blood supply.
But if the ischemia is severe and irreversible then heart cells will die which leads to MI.
Symptoms Of MI
1.severe, and crushing chest pain
2.Sweating due to sympathetic stimulation
3.Vomiting
4.Shock with decreased B.P, paleness, panic, weak pulse
5. Arrhythmias followed by ventricular fibrillation and collapse.

                                                   Continued...

ECG EDUCTION-A-ECG BASIC-

ECG INTERPRETATIONS

An ElectroCardioGram or ECG (more frequently as  EKG in which K replaces C which represents the first letter of the German word 'Kardio') is the testing of electrical conductions through the heart muscles (Myocardium) which describes the regular 'SINUS RHYTHMs' and the heartbeats in the form of line waves which can be recorded graphically.

In this article we can study all the basics of how to interpret the ECG.

Fig-2

All ECGs are recorded in graph papers that contain large and small squares. Every large square is composed of five small squares. These squares represent seconds.

Each small squares are 1 m.m in width horizontally by which we can calculate the width of the large squares as 5 mm horizontally.

The horizontal axis (the X-axis) represents time. Every 1mm square in the X-axis(the time axis) represents 0.04 seconds and every large square represents 0.04 x 5⇔0.20 seconds.

The above calculations are based on the ECG machine speed which is set up to move the ECG paper by 25 mm per second.
The vertical Y-axis represents the electrical conductions that can be recorded in millivolts and which are in the form of positive and negative deflections.
The positive deflection is the one which deflects upward and above the isoelectric line-the X-axis.
On the contrary the negative deflection is the one which goes down below the isoelectric line.
An isoelectric line is the one in which there are no deflections or electric conductions and that is a brief resting position in between two conduction cycles and that is usually represented by the T-P interval which we will understand in due course.
Again the vertical Y-axis contains the dependent variable the cardiac electric deflections in millivolts which can be calculated as follows.
On a standard ECG paper a deflection of the pointer above or below the isoelectric line with 10 small squares represents + or - 1 mV provided that each small square has a width of 1mm.
That is 10mm above or below deflection =+ or - 1mV.
From a normal ECG we can study so many important health parameters including arrhythmias and other heart problems such as atrial fibrillation, atrial flutter, ventricular fibrillation, myocardial infarction(MI), heart rate, normal sinus rhythm, sinus bradycardia, and sinus tachycardia etc.etc.
A normal adult heartbeat is 80 to 100 bpm. (beats per minute)
The normal range is from 70 to 100 bpm.
For a newborn baby it may be between 90 to 160.
A beat or rhythm is a full ventricular depolarization or contraction, which is the systole represented by the QRS complex in the ECG graph. The QRS is followed by a brief gap to another small bump deflected above the isoelectric line which is the T-wave.The T- wave is the end of one full sinus rhythm.T-wave represents the ventricular repolarization or relaxation.
T-P interval is the resting interval in which no conduction which represents the isoelectric line. The isoelectric line goes until the next cycle begins at P-wave which represents the atrial depolarization, the diastole.
To calculate the heart beats per minute you have to do the followings:-
We already know that the speed of the ECG is 25mm per sec. That means,
                            1 sec   = 25 mm
                            60 sec = 25X60=1500 mm
 Hence 1 min =1500 mm or 1500 small squares
We know that 5 small squares constitute one large square and hence in one minute 300 large squares are moved in the ECG. Count the number of R-waves which represent the heart rate per minute by this 300 sq.method.This 300 is the magic number that we can use to find out our heart rate in the standard large square method. There is another method known as a 6-sec method which we will see later.
            Before we perform any of the above two methods we must confirm that the ECG is normal with regular sinus rhythms. To do this first you take an empty white strip of a paper. overlap the strip exactly to coincide with the ECG and mark with a pen any one of the completed sinus rhythms or any of the two consecutive R-R intervals to find out all R-R gaps are equal to each other. This can be done by overlap the mark upon one by one of the following R-R intervals. If the mark fits exactly on all the R-R intervals then we can say the ECG is normal with regular sinus rhythm.
Now we can proceed with the large square method to determine the heart or pulse rate.
Method-1:-The Large Square Method:-
Spread your ECG on the table.
Count the number of large squares between any two consecutive R-R intervals.
Divide 300 by this number,
The result is your heart beats per minute.
Method-2-The Six seconds Method:-
In this method the ECG must be taken in a 6-second strip paper. Note that there are three lines on the upper part of the strip for every 6 seconds. Count the number of R-waves within these 3 lines  (6 sec) and multiply the number by ten which gives the heartbeats per minute.
This method is useful even if your ECG is not normal.
The 6-second gap can also be calculated as follows:-
Assuming that the speed of the ECG is 25mm/sec.
Accordingly we already noticed that in one minute 300 large squares have passed.
hence                                 1 min = 300 large sq.
                                    (ie) 60 sec= 300 large sq
                              then for 6 sec = 30 large sq
Hence mark down the gap which includes 30 large squires.
Now count the number of R-waves within this gap and multiply it by 10 which will yield the heart rate in beats per minute.

General Nomenclature of an ECG:-

In this section we can find the naming of the ECG parts.

Normally an ECG is appearing like this.

    

Fig-3

In the above diagram we can observe various conductions and their relationships with a normal ECG.

The electrical responses of the various parts of the heart muscle can be classified briefly as follows:-

0-Phase:-In this phase sodium ion flows inwards rapidly into the myocardial cell and depolarizes it the muscle contracted which is represented by elevation in the graph (see diagram)

1-Phase: -A short but powerful drop-in which all sodium ion gates closed and there is a powerful outflow of potassium ion from the cell with the exchange for the chloride ion which flows into the cell and the myocardium repolarizes and relaxes (note in the above diagram this phase is absent in SA and AV nodal conductions.)This phase is present only in the Purkinje fibers that are the ventricular response. This means the ventricles after a shoot up contraction undergo a brief relaxation which can be evidently seen in the ECG as S-wave at the QRS complex.

2-Phase:-This is the phase very prominent and important in the electrophysiology of the heart. In this there is a continuous potassium ion efflux and calcium ion influx to form a plateau in the cardiogram. In the above diagram you can notify this plateau as the S-T interval in ECG.

3-Phase:-In this phase the calcium ion gates are closed and continuous efflux of potassium ion. This is the rapid repolarization or relaxation of the ventricles which can be seen in the ECG as T-waves.

4-Phase:-This is diastolic depolarization in which the ventricles are ready for another cycle. The resting phase is maintained by continuous potassium efflux and slow sodium and calcium ion influx. This is represented in the ECG as the isoelectric line.

FIG-4

At the beginning of the heartbeat first the conduction starts at the SA (Sinoatrial)- node which is situated at the top right corner of the right atrium (right upper chamber) of the heart. Sinoatrial node is the pacemaker to start the heart rhythm. It spontaneously depolarizes with a slow response and spread the electrical conduction to the left atrium and down to the ventricles.

The diaphragm which separates the atria from the ventricles is totally inert and will not respond to electrical conduction. Hence the conduction from the SA node goes to the AV node directly.

But before it reaches the ventricles the conduction is paused for a while by the AV (atrioventricular) node which briefly takes time to decides to send the conduction down to the lower chambers are not. This is represented in the ECG as the P-R or P-Q interval. The AV node is situated at the left bottom of the right atrium and just above and very near to the center of the two ventricles.

Up to the AV node the muscle responses to the conduction are slow in order to give enough time to the AV node to decide.

Once the AV-node comes decided it responds quickly and passes the conduction to the Bundle of His, which is situated at the top-bottom junction of the two ventricles or at the inferior end of the internal septum to the ventricles. (See the figure-4 above)

The bundle of His quickly responds to the conduction and passes it to its branches on either side. The branches then pass it quickly and finally to the Purkinje Fibers which holds the two ventricles. The conduction passes to the ventricular muscles which depolarize quickly and powerfully contract with a sound 'dup'.The ventricular contraction is the powerful one that overshadows the atrial repolarization or relaxation. The ventricular contraction is represented by the QRS complex which masks the atrial relaxation in the ECG. You can note from the above figure the QRS complex is the main part of an ECG which exactly at the overshoot region of the Purkinje fiber (ventricular) response drawn above the ECG (See Fig-3 above)

Now we will go back to the P-wave the first part of the ECG.

From the above figure (Fig-3) the P-wave is the region represented by the atrial contraction(depolarization) which is slow and deflect to a small part just above the isoelectric line (X-axis or Time-axis)

We have already seen that the atrial relaxation (repolarization) is masked in the QRS complex.

Now come to the end portion which is the T-wave in the ECG. The T-wave represents ventricular relaxation (repolarization).

We can summarise these waves as follows:-

1.P-wave-Atrial contraction

2.P-Q interval-A brief pause at the AV-node

3.Q-wave-The brief preparation of the ventricular muscles to overshoot

4.R-Wave-Ventricular Contraction, the overshoot phase.

5.S-wave-after the systole brief repolarization followed by a diastolic depolarization to reach the isoelectric line.

6.S-T-interval-The resting phase before the ventricle relaxes.

7.T-wave:-Repolarization of the ventricles followed by the diastolic depolarization of the atria for the next P-wave cycle.

8.T-P interval-The The isoelectric line.

A brief Terminology:

1.Depolarization-means contraction of the muscles

2.Repolarization-means relaxation of the muscle.

3.Systole-Ventricular contraction (atrial relaxation)-R-wave (QRS -Complex)

4.Diastole-Atrial contraction -P-wave

5.Ventricular relaxation-T- wave

                                          Continued in the next 

A brief explanation regarding to 'Depolarization' and 'Repolarization'.