How to read ECG: Electrocardiogram Simplified

Last updated on April 19th, 2022 at 05:55 pm

How to read ECG or electrocardiogram?

All that ups and down in an ECG graph has something to say. Whether our heart is healthy or suffering from an anomaly we can detect it on ECG. But how to read an ECG? ECG is a way to study the functioning of our heart, whether our heart is beating normally or it is altered we can study it on ECG graphs.

In this article, we will try how to learn the step by step method to interpret the ECG graph. Or, if you like to watch the video instead then scroll down to the bottom of the article.

How To Read Ecg Step By Step

How to read ECG step by step

The ECG was first invented in 1901 by Willem Einthoven. Over the ensuing century, it has become a mainstay for risk stratification, disease identification, and cardiovascular management. ECG stands for electrocardiogram, it is a technology to study the function of the heart through graphs. When you visit the doctor for an ECG they will place 10 to 12 electrodes all over your chest and record the electrical activity of the heart.

This electrical activity is recorded on the ECG machine and is represented as a graph. For a normal person, the ECG will look something like this:

Every component of ECG that is PQRST has a meaning. Let us try to understand and interpret an ECG.

Cardiac cycle

For understanding EKG we first need to understand the cardiac cycle and we have already discussed in detail each and every step of the cardiac cycle. But broadly cardiac cycle passes through two major phases.

1. Systole
2. Diastole

We all know little anatomy of our heart, our heart is divided into four chambers, the upper two chambers we call as left and right Atrium. And lower two chambers are known as the left and right ventricles. Now coming back to the phases of the cardiac cycle, let us first start with systole.

Systole

This is the phase when the chambers of the heart contract to pump out the blood from the heart to different parts of our body. We can again subdivide systole into two phases.

1. Atrial systole
2. Ventricles systole.

When the upper two chambers contract we term it atrial systole during which blood from the atrium is pumped out into the ventricles. Then comes the ventricular systole when the ventricles contract to pump out blood from the heart to different parts of the body.

Diastole

The second major phase is diastole and It is the phase during which all four chambers of the heart come to a relaxation state. This is to refill the heart and prepare for the next cardiac cycle.

Understanding PQRST cycle

So what does it tell about the graphs of ECG and how to read an ECG. let us again have a look at the ECG, it has waves that pass through PQRST. One PQRST wave signifies one cardiac cycle.

P wave

In our quest to understand ECG, let us first try to understand the first wave, that is the P wave. Observe that the P wave of this ECG graph forms a plateau and is shorter in height than Q. Also, P is much more in height and has a sharper wave. P wave signifies the atrial systole.

QRS complex

After this, there is a gradual dip only to take a very sharp rise to form a tip designated as Q. It continues to rise sharply to a much greater height than a P wave and reaches the tip. This tip is designated as R where again there is a sharp dip.

When it dips, it goes a bit deeper than Q and again begins to rise to the normal level to form tip S.

This QRS forms a Complex and this QRS Complex signifies the ventricle systole. The thing we have to note here is the QRS complex is much sharper and higher than the P wave. It tells us that during ventricular systole all the contraction of the ventricles increases sharply and suddenly. Also, the power of contraction is much more than atrial systole.  

This is because ventricles have to push open the valves to pump out blood to different parts of the body.

T wave

After this heart comes to and relaxed state and there is the wave formation we call T. So the T wave signifies the diastolic phase of the heart.

Final word

When our heart is suffering from any disease the heartbeat, the rhythm of the heartbeat also suffers and it changes the electrical activity that is captured on the ECG is also different from the normal ECG graph. This is why understanding ECG is so important.

Keep Reading: ECG has hidden info of overall health status|AI can predict

Reference:

• Research titled “Age and Sex Estimation Using Artificial Intelligence From Standard 12-Lead ECGs”, published 27 Aug 2019https://doi.org/10.1161/CIRCEP.119.007284Circulation: Arrhythmia and Electrophysiology. 2019