MORPHOLOGY OF THE ECG WAVES-SELF-ECG EDUCATION-F

MORPHOLOGY OF ECG WAVES

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• The Article:-

This is the last and final step to expertise the ECG education after the identification of the ECG-waves.In this article we will analyze the morphology, physiology, and the pathology of the ECG-waves.

VALIDITY OF THE ECG

Fig-1

Before going into the heading first thing we must confirm the validity of the ECG. To check the validity we must see the correct placements of the leads. If the leads are wrongly placed or mistakenly interchanged then the whole ECG will appear abnormal leading to wrong diagnosis and treatment.
For example the nature of the ECG recorded by aVR electrode (augmented Voltage Right) is a mirror image of the ECG recorded by aVL and lead-II electrodes.
Because the aVR electrode is placed far right from the heart at the right-hand wrist or shoulder.Since the axis of the heart and its activities are all towards left this lead record the sinus rhythm upside down and which is normal as shown in Fig-1 above.
If in case the aVR records a normal positive rhythm instead of mirror image then there are problems either in the heart (Dextrocardia)or due to leads misplacements.
Dextrocardia means the hearts axis is abnormally rotated to the right or extreme right. Hence a proper diagnosis must be conducted by the doctor. If Dextrocardia is absent then the patient has to be sent back to the ECG room to retake the ECG with correct placements of the leads.

P-waves:-Morphology

Fig-2

P-wave totally represents the contractions of the two upper chambers(Atria). See Fig-2. The three types of P-waves have been shown with three different morphologies. Out of the three two are abnormals in appearances which are pathological.
The first P-wave is the normal one. The morphology of the normal P-wave as shown in Fig-2 is a half-circle bump above the baseline with not more than 2.5mm(<2.5ss) both in height and width. The bump has been equally halved. The right one-third of the side (R)represents right atrial contraction, and the left one-third of the side represents the left atrial contraction and the remaining curved upper portion is the combination of the right and left atrial contraction represented by (R+L).
The second P-wave is with a cone shape that indicates there is a problem at the right side of the heart. That is right upper chamber enlargement due to problem in the tricuspid valve(the valve in between the right upper and lower chambers) stenosis,(narrowing of the valve opening), or lung diseases.-Cor Pulmonale
The third abnormal P-wave. It is M-shaped or it may look like a camel hump. This is due to the left upper chamber enlargement due to the mitral valve (the valve between the left upper and lower chambers) stenosis.
QRS-MORPHOLOGY:
The following is the QRS-Complex which represents the contractions of the two lower chambers(Ventricles).
Any abnormality in the appearance or morphology of QRS represents the problems (Pathological) in the lower chambers. See below the Fig-3

Fig-3

This is a typical morphology of the QRS which describes the morphological changes during Right Bundle Branch Block (RBBB) and Left Bundle Branch Block(LBBB).
In the RBBB the right ventricle is not directly activated as it should be by the right bundle branch because there is an electrical conduction block. The left ventricle is activated by the left bundle branch and these impulses are conducted by the LV myocardium to the right which then contracted. In this ECG we can observe the rapid depolarization of the L.V along with a slowed and delayed depolarization of the R.V.This is clearly indicated by the first shortened widened QRS complex followed by a deep negative deflection as S-wave and then a steep positive upward deflection, the R'-wave. These changes can be observed in the V1 electrode which is viewing the heart from the right. The V-6 electrode which views the heart from the left records a mirror image of what V-1 records (see Fig-3-RBBB).The reason is very simple. Because it views the heart from the left side but the conduction is towards the right and away from the left.
Similarly in LBBB the left ventricle is not directly getting conduction from the left bundle branch instead it receives the impulses from the right ventricular myocardium and the contraction is delayed while the right ventricle contracts normally and quickly.
See the Fig-3 above. The V-6 lead receives positive impulses hence it records positive deflection (Fig-3)
QRS IN MI:-

Fig-4

In the above figure a typical abnormal QRS is presented. There is a deep negative deflection of the Q-wave and the ST-segment is elevated.
A normal Q-wave represents an impulse with a small magnitude passes from left to right at the intraventricular septum. The impulse is followed by a large impulse with a large magnitude passes from right to left which is represented by the R-wave.
But a deep negative Q-wave indicates that the ventricular contraction is delayed due to a blockade, because the impulse which passes from left to right very strong. The elevated ST-segment also indicates the irregular repolarization or relaxation of the ventricles. If the QRS looks with this morphology it means it confirms the presence and prediction of heart attack or myocardial infarction (MI)
QRS IN VENTRICULAR TACHYCARDIA:-
Tachycardia means elevated heartbeats per minute (<160 bpm)

Fig-5
Ventricular Tachycardia(VT)

In Fig-5 some of the recordings such as V4, V5, and V6 are omitted as they are also somewhat similar to other recordings except V-1, and V-2.
This is because V1 and V2 are viewing the heart from the right side.
aVR is recording a  positive deflection this may be due to the rotation of the heart axis towards the right extreme. Hence VT may be originated from the right ventricle.
In general, during tachycardia the heartbeats are irregular and the QR segment is wider and there are more R waves per minute. In Ventricular Tachycardia, in the ECG the QRS complex is wider than 3.5 small boxes (>0.12 seconds)
Also in VT the P-wave has no connection with the QRS.
There is a fusion of sinus and ventricular rhythms.
Torsade de Points:-

Fig-5A

If the VT if not treated properly it becomes polymorphic (very irregular) as shown in the figure above. At certain points sinus rhythm may return but soon the QT intervals widened (>500ms, see Fig-5A above) followed by irregular twitching of QRS around the isoelectric line may indicate Torsade de Points which will lead to fatal V.Fib followed by death.

QRS IN VENTRICULAR FIBRILLATION(V.F)

See the fig-6  below which is the ECG recorded by the lead-II.

Fig-6

Fig-6-A

See the above Fig-6 and Fig-6A which shows the ECG of VF recorded by lead-II. The morphology shows that there are no P-waves. The ventricles are fibrillating without any coordinations.
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