 Welcome back to the lecture series on bioelectricity. So, we were we are into the 26 lecture. In the 25th lecture we talked about I introduce you to the cardiac system. We talked about the anatomy of the heart and the different cell types of the heart their electrical properties the kind of action potential they shoot and we figured out that the conduction system has a different action potential pattern as compared to the contractile system and how from the conduction system action potential are transmitted to the contraction system and how this is all coordinated. So, this class is just like when we are studying about the brain people remember we talked about the activity of the individual neurons and then a small population and then at the end we talked about the electroencephalogram. The overall activity of the brain exactly the same way the heart has overall activity as of now we have talked about the individual activity of the individual circuits within of the heart the contract conduction system contractile system and there are two distinct electrical phenomena which are regulating all of them is regulating the other one is happening. But, if you put electrodes on top of the heart there you get a global phenomena of what is happening and that all falls under EKG cardiogram with the German or ECG electrocardiogram C or K which so you you kind of you know highlighted. So, the question what we are going to ask now is where we stop the last lecture is what is ECG or EKG and how it is linked to the conduction and contractile system of the heart coming back to the our slides. So, this is the question with which we are starting this class. So, now electrocardiogram or EKG by definition it represent a summation of action potential across the entire heart just remember what we did in ECG or sorry EEG electro encephalogram I told you that you put electrodes on top of your head like this you know and they do all the recordings where you get the electroencephalogram picture or electroencephalogram recordings. So, same way in EKG what you do ECG represent the summation it is the addition of algebraic addition of all the electrical phenomena and ECG reading includes interpretation of the following P waves. So, there are different waves what you see if you go to the doctor will see a P wave PR interval QRS complex QT interval and ST segment you do not get worried these words at this point will sounds to you as some Greek and Latin, but very soon it will be very clear it is a very straightforward and I am not going into the vectorial analysis of it I am just keeping it very simple for your understanding and I will give you the reference very simple reference where you can understand how this different waves are being generated it is a simple vector calculations it is not a big deal, but I am not just not touching at this stage, but I will give you the idea of it the physics behind this whole process. So, coming back to the slides. So, this is how the ECG is a graphic recording of the changes occurring in the electrical potential in millivolts between different sites on the skin the you are so these are your lids you are putting the lids on the surface as a result of cardiac activity this is how it is being measured. So, this is essentially how you are measuring you are keeping different lids the surface electrode these are all your all your surface electrodes which are on your body and which are actually picking up the global electrical signal of the heart. So, now moving on to what exactly. So, I told you that I am not going to deal with the vectorial analysis, but what essentially happens is this. So, the way the way the when the heart is beating I told you there is a pattern by which it beats first the upper chambers they sends the blood to the lower chamber from the lower chamber blood is either pumped to the rest of the body or to the to the lungs for verification through the either through the pulmonary artery or it will be sent through the aorta and pump. So, there is a pattern of event. So, if you look at this picture you will see from the SNO out here the pattern is moving like this. So, polarization depolarization polarization depolarization polarization depolarization as if there is a sea of dipole or or just like a dipole like you know as if there is a moving dipole I mean if you follow this. So, as if this wave is moving positive negative positive negative positive negative positive negative likewise. So, this is there is a wave of dipole. So, if you see the dipole causes the current flow in the surrounding body fluid between ends of the heart resulting in a fluctuating electrical field throughout the body and I have given you a reference you can people can go through it after conduction begins at the SA node cells in the atria begin to depolarize this creates an electrical wave front that moves down towards the ventricle this is essentially what is happening because initially your upper two chambers are getting filled followed by the blood moves to the lower two chambers from there it is either distributed to the rest of your body or sent for purification to the to the lungs. So, this is exactly what the slide is telling you followed by depolarized cells behind the separation of charges. So, this is very important to read the separation of charges results in a dipole across the heart the large black arrow shows its direction you see follow this black arrow. So, this is how the direction is moving. So, detection of this change in electric field using surface electrode is essentially what you do in the ECG recording and the vectorial component of these different dipoles using a simple mathematical transformation you get the ECG waves where we are talking about p waves and q t interval q r s complex and all those things what would be dealing now. So, now as you know the geometrically what is happening. So, at different stages of this excuse me at different stages we are getting a different vectorial summation and which will be coming next is what we essentially measure in ECG or EKG is using electrode on the surface of the skin we detect the voltage of the electric field remember this. This is what provided the electrocardiogram or ECG or EKG now moving on how this wave is generated now they are coming to those all those greek and latin words what scared you people. So, this is in millivolt because if you go back. So, what you are measuring you are measuring the voltage of the electric field and electric field is generated out here. So, if you follow this diagram there is an electric field which is a moving electric field as if the dipoles are moving polarization depolarization and following this arrow and. So, you will be measuring the voltage. So, here on your y axis you have the millivolt and these yolo are showing which part of the heart is excited and which part is not excited. So, the first when the upper chamber out here is excited when you see this is the trace in the blue you see the trace the electrical trace the overall electrical trace on the electrode followed by this one when both the upper chambers are partially activated. So, it forms a small hum out you see this hum this is the p wave when and this p wave becomes complete when both the upper chambers are completely excited. So, yolo is indicating the complete excitation followed by this excitation moves on to the lower chambers out here and this green showing it is no more excited it is it has already send of it is in the process of you know sending the liquid or the blood to the lower two chambers out here. So, it is a spreading in the lower two chambers and in the meantime you see this p and there is a q r s you see this overall electrical impulse is showing like this you could follow this. So, this is what is called q r s complex and this is all the recording those surface electrodes what is happening followed by the q r s complex this is again the repetition the q r s complex where the whole lower two chambers are completely excited or completely you know active followed by from the lower two chamber blood is now pumped to the in this in the process of getting pumped to the either to the aorta or to the pulmonary artery this is where your t is coming you see this t out here and if you follow this diagram you see this is the ECG trace. So, first of all this red area is showing which part of the heart is excited and the contrast you have the ash color. So, it starts here p then you have the p q then you have the q r s complex then again the q r s is further going through q r s is a long complex. So, see how this whole thing is building up this what you see this was kind of it when slightly more in advance. So, here you can build up the whole story how this whole graph of p q r s complex is forming. So, the p complete formation of the complete p now the q started now r s is going up it is further coming down and then it is ending the s t and then the t wave coming through and this is the complete p q r s complex. So, this is what essentially is the change in the electric field what you see which is being measured. So, the definition wise now see the revisit the definition of it using electrodes on the surface of the skin we detect the voltage of the electrical field this is what we called as the electrocardiogram or the ECG and this is the whole process how what. So, whenever a doctor sees now what are the practical significance of this whole process say for example, you see two p waves. So, one p wave followed by another p wave and then the q r s complex is coming what does that mean think of it essentially that means you need more power to pump the heart pump to pump the blood from the two upper chamber to the lower chamber it means something very significant that it means in your pacemaker circuit or in your conduction circuit there are blockages or there are damages because then only you need more energy to pump this or say for example, you I was telling you that what are the things you look forward to here you are suppose you have two p waves or your p r interval is longer or your q r s complex have some you know some kind of anomaly. So, this is the situation which doctors look. So, whenever the doctors if you see the doctors whenever they took taken ECG trace they kind of look for all those things whether, but let me tell you there are certain things which ECG can tell and there are certain things ECG will never and we will come to that what the ECG pattern can tell and what it cannot tell. Now looking at the ECG pattern of sinus rhythm. So, this is how it looks it is much more graphically much more well represented you have the p waves out here in green you see that followed by the p r interval out here p r p r interval out here sorry p r segment out here and the p r interval out here I am sorry and then you have the q wave you see this orange color then you have the r which is the complete red then you have the magenta which is showing the s s component and then you have the s t segment and then you have the t wave. So, this is how the p waves q r s and t waves this is and when there is a normal heartbeat that is what what a doctor sees when there is a fast heartbeat. So, basically the you see the frequency has increased and then there is a slow heartbeat the frequency has decreased and when there is a irregularity this is what the doctor looks forward to. So, this one whole figure can give you a complete idea about the whole p q r s complex and what the what the doctor really looks into whenever they see your you know ECG trace this is what they are looking forward to a normal heartbeat a fast heartbeat a slow heartbeat or a irregular heartbeat and what they essentially look for there is a p wave there could be I told you there is there could be a situation where there could be two p waves or you could have a p r segment slightly more. So, there is at it means there is a delay in in sending the message to the q r s to the lower chambers or you have a s t segment which is slightly more it means recovery time is taking is more or you have a larger q t interval or the t wave has some issues. So, this is what in a sinus rhythm a doctor looks forward to now p wave what these individual waves stand for the p wave stand for the depolarization of the atria p r interval time from the onset of the atrial depolarization of or within bracket the p waves to the onset of ventricular depolarization because I told you that atria say this is the process of depolarization depolarization depolarization depolarization depolarization depolarization. So, the first part is the atrial depolarization the upper chambers they are getting depolarized where the p waves is getting generated if you correlate this with this picture see look this is the depolarization process which is going on. So, now coming back. So, this is where atrial depolarization to the onset of ventricular depolarization duration of the a v conduction is hundred twenty two two hundred millisecond. So, if anything changes here it means this is the range then there is a problem now comes the q r s complex duration of the depolarization ventricle of the ventricle of the lower chambers is less than hundred twenty milliseconds this is where q r s complex if you go back see this is the q r s complex out here ventricular depolarization taking place look at this very carefully coming back to the ventricular depolarization this is where the ventricular depolarization takes place then comes the q t interval here is the q t interval which is essentially is the depolarization repolarization of the ventricles. So, the wave has moved from the lower chambers all the way the blood has been now pumped either to the lungs or to the atria depending on from which side it is going through to the aorta sorry. So, the depolarization and repolarization of the ventricle which is less than four twenty milliseconds and then the p r interval. So, this is your p r interval duration of the ventricular cardiac cycle and indication of the ventricular rate. So, this is what this individual wave stands for coming back to the atrial fiber and ventricular action potentials. So, as of now we have talked about the these are the action potentials of the individual cells this is the global picture and you can in this you can put the you know the action potentials of the conduction system. So, here is the comparison between but let me tell you this is just the global picture and this is the individual cellular picture atrial and the ventricular action potentials. What ECG tells now this is very important to go through very carefully ECG can tell you about the anatomical orientation of the heart is the heart anatomically in the right hand is the wave moving from the atria to the ventricles relative size of the heart chambers it can tell because depending on the time if you look at the time window it can tell you relative size heart rate that you have already seen it could tell you the heart rate is it normal heart or a fast heartbeat or a slow heartbeat or irregular heartbeat. It can talk to you about the rhythm you have seen the rhythm it can talk about the origin of excitation this is exactly what I was trying to tell you that if you have two p waves what will happen it is a defect it is a there is a problem there is a pathological situation spread of impulse how the impulse is spreading because you can you have seen that it is all a time bound game. So, there is a time factor involved out here. So, based on the time factor you should be able to say that is the impulse moving in right time or not then the decay of the excitation and any disturbances of the above event not the cause it cannot tell the cause it can only tell that there is a disturbance it cannot tell you the reason for the disturbance. So, ECG gives no direct information about contraction and pumping efficiency of the heart please do remember this ECG has absolutely no clue from ECG that what are the mechanic or what are the mechanistic damage or problems with the pumping efficiency of the contraction coming to the heart pathology where all the pathology can take place there are different places where the pathology can take place the SA note there could be a blockage there could be lesions you could see all these red lines what is showing there could be lesions out there these lesions could or there could be a blockage out here. So, all the red lines. So, this circuit could have discontinuity at any point between P and AV note between sorry SA and AV note there could be a discontinuity SA note may not be you know beating at the right frequency there could be blockage there could be lesions there could be you know something very unusual in an expression of the ion channels. So, now coming to the temporal correlation between action potential duration at QT interval on the surface ECG. So, this is what you are seeing the ECG traces and if you look at the time this is just a comparison of the time window what is the time window we are talking about now and this is an action potential this is the ventricular action potential where you see the rise of the just this is the recap of what we have already done the moment of the sodium ions and but mind it there is no functional as such you cannot really see this and make any prediction about it or see this and make any prediction about this. This is just to give you a temporal correlation just to give you the time window of an action potential and a ECG trace how much close or how much far away they are from each other in terms of the time that is it this is nothing to do with the functionality because this is a purely purely this action potential is purely a cellular phenomena and this is a holistic phenomena of the whole heart. So, coming to the different part of it atrial excitation which is taking place which are the location excitation across the AV node and excitation of the ventricle begins just there are different ways I am giving you so that it helps you to you know kind of appreciate it far better now coming to the control of the cardiac functions. So, the cardiac function is controlled by mostly the sympathetic and the parasympathetic conditions. So, if you see that there is a sympathetic stimulation increases contractility frequency conduction velocity and irritability. So, this is the whole circuit. So, here you get an idea about the sympathetic systems where the sympathetic afferents are you see the vagal nerves motor neurons you see 10 afferents which are coming here you see the 9th afferent which are coming here to the carotid sinuses and here you see the sympathetic afferents which are coming and influencing and they all do through beta 1 receptors as well as there is an acetyl choline transmission which is taking place. So, mostly it is a sympathetic afferent noradrenaline which is essentially responsible for you know regulating and this is this picture is very important because this is the these are the only spots where the nervous system is controlling the heart and these are very hot pharmacological targets the which controls the frequency of this conduction note and this is all of these are mostly regulating the contractile the sorry the conduction circuit or the pacemaker circuit of this whole thing. So, coming back what are the problems if the heart is not functioning one of the option is that we have stem cells which will help you to you know there are two possible let us enumerate the problems first either there could be a problem in the pacemaker cells. If there is a challenge in the pacemaker cells your option lies you implant artificial pacemaker which will generate signals and will ensure that the conduction circuit functions properly this is one root. Say for example, there is a problem in the contractile element if this problem is in the contractile element then option is that you have to replace that patch of the heart or that part of the heart by a contractile cell. So, you have to grow the stem cells to form contractile element you have to incorporate them at that part of the heart like a you know kind of a patch and that patch will eventually will get integrated into the into the myocardium if you remember that myocardium picture what I showed you so if I go back now to that picture which will make more sense now in the light of this what we have now discussed let me go now think of it. So, any of these parts myocardium is not functional. So, that is where you have to put those stem cells now in the light of this this picture will also make more sense this cardiac progenitor cells these cardiac progenitor cells could be implanted at a specific sites which will eventually will you know incorporate or form the contractile element which will essentially will lead to you know the repair of that particular part of the tissue which is kind of getting damaged this is one root apart from it there is lot of work which has been done by a company called a bio cord they have worked on. So, these are the contractile element which are another hot seat of research for the stem cell biologist were trying to make these kind of tissues and use them as patch to put in that part of the heart where there is a damage. Now once again let me just scroll down other option is if one goes for the artificial heart you develop these kind of devices and the pretty much work like this is the bio cord the artificial heart systems they their pouches as you could see this is an exam the picture is showing one such device with different chambers in the valves and there they are regulatory valve there is a external battery pack outside your body this is under the extreme situation your heart is not functioning it has internal rechargeable batteries it has internal control unit and it has wireless energy transfer systems where you could see an artificial heart mechanism this is where this is functioning just like those four chambers are functioning you have exactly the same module out here in the artificial heart and I have given you a fairly good amount of you know informations which is available on the internet or in different books which will give you an idea how these kind of artificial heart could be incorporated into the system so as so that you know in case of extreme emergency where there is no room left you know you can put these kind of you know organs which will get incorporated into it and could help the person to survive I mean those success rate is very low as of now but you know that is part and parcel of the whole research itself it will take time before we are in a position to replace a damaged heart or develop something which is using regenerative medicine tools which is something very close to the machine which is functioning for you remember in the first lecture of this fragment I told you 100,000 times per day that is something that is a feat which is just unimaginable feat what our heart kind of you know undergoes every day so coming back so this is basically where I will be closing in so let us summarize what we have discussed so in these last two lectures we talked about the anatomy of the heart the four chambers we talked about the valves which are present there in the if you remember all the different valve tricuspid valve bicuspid valve material valves we talked about the circulation local circulation in terms of systemic sorry in terms of the pulmonary circulation as well as the systemic circulation pulmonary where it involves the circulation between the heart and the lungs then we talked about the circulation from the heart to the rest of the body then we talked about the different cellular component the pacemaker cells the contractile cells the endothelial cells and at the end we talked about all the sympathetic nervous or regulation of the heart then we talked about the individual electrical signature of these conduction system and the contraction system and we did a comparative action potential analysis of contractile system conduction system and within the contractile system we made a comparison between skeletal muscle and the cardiac muscle after this we talked about the global electrical activity of the heart in terms of the how the electrical field is changing just as if there is a moving dipole pooled polarization dipolarization polarization likewise and from there we talked about how the EKG traces are being generated electrocardiogram traces and then we talked about what all the EKG traces can tell you what the EKG traces cannot tell you what are the informations gathered by the physician after looking at the EKG traces and how the EKG traces frequencies changes depending on the physiological status of your body then we talked about the different pathological situations and we talked about the end we talked about what are the different strategies in terms of using a pacemaker to compensate for the compensate for the irregularity of the conduction system and in case of a damage in the contraction system putting cardiac patches using stem cell therapy or regenerative medicine therapy and in an extreme situation you may need to resort to artificial heart that bio core model of artificial heart so overall the take home message from these two fragment is end of the day it is those individual ion channels which dictates the electrical activity of these different cell types of the heart and I will be providing the specific ion channels which are responsible I will be providing you those specific ion channels which are responsible for the electrical activity of the conduction system in one of the nodes and another critical thing the spontaneity of the intrinsic ability is attained because of the inherent ability of the conduction system to stay at a resting membrane potential of between minus 40 to minus 50 millivolt. So, this is the overall summary what we kind of you know developed after going through this lecture session and we go through the nodes and so we will close on this before we move on to in one of the lectures we will be talking about the man machine interfacing where nervous system will be interfaced with the how it has been interfaced with with the computers and we will talk little bit more about the cyborgs and the robots and everything thanks a lot.