 You must have seen in movies or TV shows that a person all of a sudden Experiences severe chest pain and then he is rushed to a hospital where he's hooked to a machine and You get to see that there are fluctuating lines on the screen of the machine And and then you hear sounds like peep peep peep, and then along Peep Sound with a with a straight line That indicates that the person is no more now What are these lines and What is this machine called and? How is this machine able to tell that the person is no more through a straight line? Well, we will discuss all about it in this video. Okay, let's begin So this machine is called an electrocardiograph So you get to see the word cardio in it that means it is related to heart, right? So this machine can read the activities of the heart the electrical impulses that the heart generates and for this electrocardiograph to work some leads are attached to the wrist and ankle of the Patient and then through some wires They are attached to the machine and then the machine reads the electrical activity now it is natural for you to wonder How a machine can read the electrical activity of the heart through any other body part like the wrist or the ankles? Because that is where we have placed the electrodes Well, I had the same question and I learned that the body fluid that we have They are awesome conductors of electric waves So the electrical impulses produced by our heart which is placed deep inside our body is very Very faithfully conveyed to the body surfaces through our body fluid So our bodies are awesome conductors And that's the reason your parents would stop you from putting your finger into electrical plugs when you were young remember So the body fluid does the magic it brings the impulse to the body surfaces And if we put electrodes in any part of the body this machine will be able to pick up the electrical activity of the heart But again, whatever it reads. Do you see how it represents through these lines fluctuating lines? So now let's try to learn the language of the electrocardiograph Let's try to decode what these peaks and lows are referring to okay So the peaks and lows refers to the activities of the heart, which means it refers to the cardiac cycle Right and what all happens in a cardiac cycle? The first even that takes place is that the SA node it gets activated It sends down an electrical wave that contracts both the atria. We call it atrial depolarization Now this event is shown by the electrocardiograph as an inverted U shaped curve. We call it the P wave Now after the atrial depolarization the next event is the AV node activation And this activity is shown by the electrocardiograph as a single straight line Okay, and this straight line is called the PR segment From P to R and where is R? We will get to see in the next cardiac event. Okay The next cardiac event is the activation of the parkin g fibers Which leads to the contraction of the ventricles So the third point will be parkin g fiber activation and ventricular depolarization Contraction is also called depolarization. And this event is shown by the electrocardiograph as A very high peak it goes down first Up and then down and up again It is called the q r s complex Okay, the next thing that happens is that the ventricle it goes back to its original relaxed position Right. So the fourth point Will be ventricular repolarization relaxation is also called repolarization This again is a small electrical event, which again looks like the first peak We call it the t wave But do you see I have left a gap here? That is because there is a part between s and t We call it the st segment This is nothing but the time between the ventricular depolarization and ventricular repolarization And in this time there is no electrical event happening in the heart It's a very short duration, which is represented by a straight line by the electrocardiograph So a single cardiac cycle is represented from P to T But in real life this representation is done on a graph paper, which we call the electrocardiogram or ecg It's quite similar to the name of the device, right? It was electrocardiograph Now students often confuse with both these terms because the graphical representation do not have the word graph in it But the device has right so be very careful when you write these down in exams Okay, now when I learned about these peaks and lows for the first time I was really curious as to why can't they be of the same length because they are all electrical impulses Of the heart, right? Why can't they be of the same length? Well, I found out that The electrocardiograph it works on the principle of a galvanometer You must have read about it in physics, right? This device can record the intensity and direction of electricity Higher the intensity higher will be the peak and talking about direction Do you see the upward and downward movement of the curve from the mean? This is showing the change in the direction of the electrical wave Okay And also if two electrical events take place simultaneously in the heart Then the electrocardiograph records just one the one with a higher intensity And that is the reason we have not mentioned a very important part of the cardiac cycle in these four points Can you pause the video and think of what that point is or what that activity of the heart is? Okay, so before telling you the answer Let me tell you that if any muscle in the heart gets depolarized it repolarizes as well Right, but did we mention about atrial repolarization anywhere? No, right We did not mention that because the atrial repolarization and the ventricular depolarization They both took place at the same time and the intensity of the ventricular depolarization was so high That it marks the atrial impulse So if two events take place simultaneously the electrocardiograph will only record the one that is of the higher intensity Therefore in this graph, we are not able to measure the atrial repolarization So these waves and segments are all based on the direction and flow of electric waves and its intensity Okay, and this also brings us to our opening question as to how a straight line can depict that a person is no more So if a person is alive his heart must be working and he will have this ups and downs in his ECG But if the line is straight without any ups and downs That means the heart is not pumping and without a functional heart the person will definitely be not alive, right? Okay, apart from knowing if a person is dead or alive. Is there any other significance of an ECG? Well, yes, there is By counting the QRS complex in a given period of time in an ECG One can calculate the heartbeat of an individual And since the ECGs obtained from different individuals have roughly the same shape Any deviation from its shape indicates a possible abnormality or disease So this was all about electrocardiography or ECG