 Welcome back to the lecture series in animal physiology in a pitel section. So, we are into the section 3 and today we will be talking about the third lecture in section 3, which is pretty much the concluding lecture about the heart. So, we have talked in the first lecture about the structure of the heart and the cellular details, how the tissues are arranged in the heart, what are the different valves, what are the different chambers and how the blood flows from one chamber to another and likewise. In the second section, we introduce the conduction system and the contraction system of the heart and in depth we talked about the pacemaker, which are part of the conduction system and the contractile element, which are part of the cardiac myocytes, which are part of the contractile element and we talked about the action potentials and everything. In the last class, we concluded the last class talking about how the ECG is being generated and in this class, what we will do? We will talk about the conduction circuit and how that circuit exactly determines how the signals will move from one end of the heart to the other end of the heart. So, moving back, if I redraw the circuit of the, so these are the right atrium, right ventricle, left atrium, left ventricle and this is where in the last class, we talked about the SA node and SA node has this whole circuit, here you have the AV node, from AV node the circuit moves like this. So, this is the SA node, this is the AV node, this is the bundles, this part is the bundle, what you see out here and these are the parking fiber and we have already discussed that the stimulation out here, the kind of you know the wave fronts, which are generated all along are spread out like this. Now, we will be systematically talking about how these wave fronts are exactly moving across the heart from this end to this end. So, you have to put the arrow, the arrow is like this, the wave front is moving like this, following this green arrow. So, this wave front movement is a time dependent phenomena and now what we will do is that, we will be talking about that time dependent phenomena in it. So, it starts from the SA node, the first step is at the SA node. From the SA node, it moved to the atrial synchium. So, in other word sorry, atrial synchium. So, basically all the atrials, atriums or the two upper chambers are kind of getting stimulated. From there it moves on to the junctional fibers, which is basically just before the AV nodes. From there it moves on to the AV node, from the AV node it moves to the bundles, AV bundles, anti-ventricular bundles. From the AV bundles, it moves to the P F, the purkinje fibers and from there it moves on to the ventricular synchium. All the ventricles kind of the complete ventricular chamber kind of gets excited. So, if this is start at 0 milliseconds, by the time it reaches the AV node, it is 100 milliseconds. There is almost 100 milliseconds or 100 milliseconds lack phase and by the time the ventricles kind of gets completely stimulated, it is around 225 milliseconds. Now, what we will do? I showed you like this. Now, what I will try to do? I will draw the whole thing, so that it makes more sense and what I will do? Simultaneously, I will draw the… So, let us start with this. Let me draw four chambers. That will be easy. Three… Let me redraw it because I cannot accommodate here. So, let me see. One, two, three and four. Fine. And on the other side, what we will do? We will have the… Suppose you have electrode, surface electrode on top of the heart, how you could measure it. Two, three, four. The y-axis is talking in terms of the volt. 5 volt, 10 volt, 10 volt. Similarly, this one ends here. The next one, again same way. 5 minus 5. I am just putting in minus 5 because of the space constraint. And these are all n-villivolt. And you have same way, 5 minus 5. And the x-axis is showing you the time. 5 minus 5 minus 5 minus 5. Fine. So, these are the four graphs which you could see. Now, what we will do? I will try to plot it how this looks like. So, this is the time when the stimulation is involved here. This red shading, what I am doing? So, you are right atrium. If I put this as r a, this one, and r v. And this is r l… Sorry, this is l v left wing. And this is… This is ventricle. And this is left atrium. So, this is the first step. And what you see on the trace is like rise like this. So, this is happening. So, the time, let me put the time on the y-axis. So, around 200 milliseconds, 200 to 400 milliseconds, something like this. So, the next step comes when both this left atrium and right atrium both are completely excited because of the propagation of impulse from the conduction system. So, what exactly it does is that whenever the conduction system, conductile system sends a stimulus to the contracting system. So, all the cardiac myocytes which are across this, all the shaded red region, they start contracting. And we will come to that how that is being governed. So, by the time it finishes this, the curve shows you something like this. Next what you observe is out here, when the ventricles starts getting the contraction because of the impulse from the conduction system. And this is the stage when you see, this is already done. Then you see like this. Then you see a big rise and something like this. This is the third phase. Now, from here we move on to the fourth one. Sorry, actually I drew it wrong. I should have drawn it on the lower line. Sorry, let me redraw it. So, it is like this. Now, this is right. Now, comes the fourth phase where your lower half of the ventricle kind of getting the stimulation. So, it is reaching through. And now, if I had to redraw the circuit, circuit is like this. I am redrawing it for all of them so, that kind of this is how it is happening. So, initially the stimulation was out here. If you go through it, it was here at this zone. Then the stimulation completely spreads on the other side. And then the stimulation out here. And then now the stimulation is at this fag ends. So, at this fag ends, when the stimulation is there, what is happening? The graph is getting completed. This moves up and then with a gap you see. So, this trace what you see is a characteristic ECG trace. And now we will give the nomenclature for it. I will redraw this particular graph in a bigger platform. So, that will give you an idea how that looks like. This is how a single ECG or EKG electrocardiogram or or electro EKG or ECG, which so you call that exactly meant. And if I go back to the previous diagram, give the time constrained out here. So, this event what is happening? This is happening 0 to 50 milliseconds. And this events kind of get over by 150 milliseconds. And from here, the first phase goes through 175 millisecond. And by the time it ends here, it is around 225 milliseconds, which tallies up with the previous one. If you look at it while I was putting all these values out here, this is what was happening. Now I showed you in the diagrammatic manner, how the electrical impulses are getting transmitted. Now, coming back to giving the nomenclature, what is essential? This one is called P. Let me use another color for better understanding. This one is called P. This one is called let me put it like this. This one is P. This is called the QRS complex. So, here you have the Q, here you have the R, here you have the S, QRS complex and this is called P. This is a characteristic EKG trace looks like P, QRS complex. And within that, you have the different terms, which are used. This is P and from here to here. So, this one is called once again. This one is called PR, PR in PR segment. And this one is called PR interval. Then you have this QRS complex, which is this from here to here. This one is called QRS complex. And from here to from here to this part, it is called ST segment. And from this part, from this Q, where the Q starts to the end of the T, this is called QT interval. So, this what is exactly is the QT interval is the QT interval is the time required for the ventricles to undergo a single cycle of depolarization and repolarization. Depolarization and repolarization. This is what the QT interval is all about. And what is the PR interval? Come back. So, the PR once again, the PR interval is basically extent from the start of atrial depolarization to start of QRS complex or which could be also called ventricular depolarization. So, these are some of the things and based on this, if you look at the EKG trace. So, this is P, this is QRS complex and this is the T. Based on that, if PR interval is the time required so this is one cycle. So, the followed by the next cycle again a P in a Q. So, cycle one cycle two. So, if they are much more closer like this, so there is a lesser time gap between the two cycles. So, that is when the heart is beating very fast that is a fast heart rate and if they are far apart then there is a slow heart rate. And if it is irregular if the time gap between these two is irregular that is a irregular situation which we falls under cardiac arrhythmias. This is the basic understanding of this fall under cardiac arrhythmias where there you have irregular heart rate. So, you could have the fast heart rate, you could have a slow heart rate, you could have a irregular heart rate and that falls under all kind of arrhythmic condition. So, what really arrhythmia really means? So, this is very interesting to understand. So, one more thing before I talking about the PR interval when you talk about the PR. So, generally whenever PR is more than 0.25 seconds sorry 0.25 seconds there is some kind of a problem why is it so? So, let us physically understand the process. So, what exactly is happening if this is the heart we have and this is the circuit what we are talking about with AV node, SA node and purkinje fiber and everything. So, the signal is following a certain speed with which it is spreading out here, spreading here, spreading here, spreading here and these signal spread decides in what sequence the atrium will empty its blood to the ventricle from the right side to the right ventricle from the left side to the left ventricle and at what rate the left ventricle and the right ventricle will pump the blood to their respective target from the left of course it will go towards rest of the body and from the right it will go to the lungs. This whole sequence of event is very very tightly regulated in terms of time the volume and this is continuously being regulated by this conduction system of the heart. The conduction system is that very important here because it sets the tone by which the heart is going to continuously beat for rest of your life and it will adjust whenever there is your heart is will be beating fast because of some physical exercise or some x y z situation or you are sleeping when the heart may beat slower likewise. So, that tone is very very important for us to understand and based on simple EKG trace you really can figure out that what is the status of the heart and there are certain things what EKG can tell and yet there are certain things which EKG cannot tell and will talk about what EKG can tell you and what EKG cannot tell you what EKG or ECG can tell you. So, these are the things what EKG can tell you first it can tell you the and please be very careful on this one anatomical orientation of the heart this is EKG can tell you straight away of the anatomical orientation of the heart this EKG can tell you first thing second thing EKG can tell you relative size of the different chambers of the heart of the different chambers of the heart this EKG can for sure tell you what else EKG can tell you it can tell you the heart rate this EKG definitely can tell you fourth what can tell you the rhythm of the heart or H Y T H rhythm of the heart fifth it can tell you origin of excitation from where the excitation is getting originated fourth it can tell you about spread of impulse how the impulse is getting spread is there a blockage in the pathway or anything spread of impulse it could be worked out from the EKG traces spread of impulse apart from it what it can tell you the decay of excitation because it is an electrical impulse. So, you can measure it decay of excitation what else it can tell you it can tell you about the deviation from these different events deviation from these events what EKG cannot tell you this is very important what ECG or EKG cannot tell this information cannot come from an EKG this is what it cannot tell you contraction and pumping efficiency and that makes perfect sense because the heart contraction is a function of the contractile system of the heart and the pumping efficiency is based on the contraction process. So, those things can never be predicted by the conduction system conduction system can say how the impulse will move in what direction it will move how it will what will be the time gap from one point to the another point like from s a node to a v node there could be a situation when you may see two p waves followed by the q r s complex you can immediately tell that if there are two p waves it means the atria has to put more pressure it. So, it means in other word it means there is the blockage or there is a damage in the pathway you see from a v node to sort from s a node to a v node you see those three pathways you know there may be some kind of a blockage by which you need two p waves you need more energy more impulse to you know make the atria pump it to the ventricles those things can tell but what it cannot tell you always remember this the contraction and the pumping efficiency can never ever be predicted by seeing ICG trace this thing is exceptionally important for you guys to understand because it is something to do with the heart attack and I will come to that what really heart attack means and what ICG can never tell you. So, from here let us move on to the next slide which is very important in terms of how the different volumes are changing this is this is very important there are two terms. So, one of the terms I am going to so will be the called cardiac cycle before you understand cardiac cycle there are two terms which you need to understand one is called systole or somebody some of the people call it systole or diastole or diastole this is very important what is systole and what is diastole systole is contraction of chamber in this situation it could be atrium or a ventricle left or right diastole means relaxation of a chamber this is what is meant by systole and diastole. So, this systole and diastole the cardiac cycle is regulated by the conduction system. So, how it all starts is this cardiac cycle is regulated by the conduction system. So, how it is being done let us systematically go through step by step one second. So, it starts let us put a start point somewhere let us put a start point here. So, the first thing which happens and this is at 0 millisecond the first thing what happens is atrial systole begins this is the step when the atrials which are all failed they start to contract then phase if this is a then stage b when around 100 milliseconds what is happening is that atrial systole continues atrial systole actually ends and atrial diastole begins this is phase two and the phase three is C I am putting it as C. So, V that is the ventricular ventricular systole begins that is the phase one this is the time when the blood has moved out from atrium and this is all over this place what I am shaded just now this is the time when the semilunar valves along the ventricles the pulmonary semilunar valve and the aortic semilunar valves are closed. So, I am putting at SLR closed. So, in other word what is happening inside the ventricle there is huge amount of blood at that stage. So, it is all contracted. So, that is the first phase of the ventricular systole I move on to the next slide with the phase D coming back that is the ventricular systole phase two. So, this is the time when the pressure of ventricular pressure increases pressure reaches maximum and it is atrial systole. More than aortic pressure and or the pressure of the aorta of the arteries. So, this is the time when semilunar valve starts to open then comes the phase E which is around 35375 milliseconds that is the early ventricular diastole and followed by the F phase which is late ventricular diastole when they are relaxed phase around 800 milliseconds. So, this whole cardiac cycle this continues in a fashion and I will give you another diagrammatic representation of it which will help you to understand how it looks like. So, let us draw a circle like this and start with phase one the atrial systole I am putting at AS followed by atrial diastole AD and then there is a phase neither diastolic not systolic it is it is kind of stand out there. So, it starts at 0 and this is at around 375 milliseconds where is on the other hand in terms of the ventricular diastole it continues from here the ventricular systole sorry around this is the ventricular systole phase around 375 and from here it moves on and this is the ventricular diastole phase which is around 100 milliseconds and this is 375 and this one ends there at 800 milliseconds. So, this is how it goes. So, physically you have to understand what is happening is this is the heart the first thing what happens the blood starts coming here it is filled with the blood both of these there is huge amount of pressure while it is processing. So, initially the blood is low and then the blood grows up the concentration of blood increases. So, then it reaches a peak pressure then what happens from here the blood starts moving to this chamber moving here. So, when it moves here. So, the blood is slowly getting depleted here blood is slowly getting depleted into this zone and the blood is filled in this zone. So, initially this was in a pressure it was in systolic systolic phase then it moves to the relaxed phase which is diastolic phase. Whereas, this one which was initially in a diastolic phase moves to the systolic phase and then when it throws the blood out this goes to the lungs assuming that this one is the left right side and this one goes to the aorta then this enters again a diastolic phase. And this whole sequence of event systolic diastolic systolic diastolic for the for the atrium and the ventricle the sequence of events is being regulated by that wonderful contractile circuits which I am repeatedly trying to draw to kind of make you understand why this is. So, very important that this has to be regulated in a sequential manner otherwise things will go out of context and we will suffer from cardiac arrhythmia and several other problems. So, now what I will do I will super impose I will super impose the p q r s graph with the systolic and diastolic. So, here you have. So, this is the phase of atrial diastole and I am not writing because there is not space to write the full form. So, I am just bear with me in understanding this follow the lectures you will be able to understand and this is the phase of atrial systole that again from here starts your atrial diastole till the next p starts. So, this is p let me mark it this is p this is q r s complex and this is d till the next p starts again we are into the atrium diastolic phase. Whereas, on the other hand if I see what is happening in terms of the diastolic the ventricular diastole. So, this is ventricular diastole phase and this one continues as ventricular. So, this is the ventricular systole phase and again the ventricular diastole phase. So, if you correlate both of them where a let me put it a stands for atrium and v stands for ventricle and d stands for diastole and s stands for systole. So, this is how the you can put the filling of the atrium sending the blood or the movement of the blood from the atrium to the ventricle and vice versa the filling of the ventricle and the emptying of the ventricle in terms of atrium diastole, atrium systole, ventricular diastole, ventricular systole and this is how you plot it with respect to the electro cardiogram traces and this is how it looks like and this is exceptionally an important for you to understand that it is a very well coordinated system and any kind of problem in this leads to a series of complications. Then from here we will move on to the next phase of it which is our cardio dynamics, but before I move on to the cardio dynamics I want you to touch couple of more stuff here. So, let us move on to the cardio dynamics I will come back to that what is cardio dynamics. So, before I move on to the cardio dynamics you have to realize the bigger vessels within the heart among the chambers of the heart are the are the ventricles. How much blood a ventricle will accommodate is exceptionally important. So, here I will give you some terminology and then I will explain how those terminologies can be used to understand the efficiency of the cardiac output. The first terminology I will give you is end diastolic volume. Let me write it down end diastolic volume what end diastolic volume means it is the amount of blood in each ventricle at the end of ventricular diastole or this is basically start of the end of the end ventricular systole. The next term is important is ESV end systolic volume what this means this means the amount of blood remaining in each ventricle at the end of the end of ventricular systole or the start of ventricular diastole. These two definitions are exceptionally important for you people to understand that is something called SV or stroke volume. Stroke volume is the amount of blood pumped out of each ventricle at the end of the end during a single heartbeat and expressed as EDV what we just now explained minus ESV end diastolic volume minus end systolic volume that gives you the stroke volume and then the ejection fraction ejection fraction is the percentage of the ventricular diastolic of the EDV end diastolic volume represented by the SV or stroke volume. From here what we will do we will measure the cardiac output cardiac output this these parameters are very important for cardiac output. So cardiac output is expressed as milliliters of blood per minute. So CO if I represent it as CO CO or cardiac output is equal to the stroke volume stroke volume multiplied by the heart rate. So heart rate is explained by beats per minute and ml per beat stroke volume. So say for example if we get two values say for example you have stroke volume of say 80 ml per beat and you have heart rate of 75 so that sums up to approximately 6000 ml per minute which is around 61 A per minute. If I just change the unit so cardiac output is equal to stroke volume multiplied by heart rate. So what are the factors which are governing heart rate? So as we will be touching in the endocrine system there are hormones which regulate heart rate and there is a autonomic nervous system. So at this point we are not discussing in depth because I have not touched nervous system. So once I will come to nervous system I will come back to this autonomic innervation. This is very important for you to people to understand and what dictates stroke volume stroke volume is dictated by end systolic volume and end diastolic. Volume these two are the factors which governs the stroke volume and there is another factor which decides what will be the stroke volume and that falls under and there is long back this is very interesting something called Frank Sterling law. So it is worth discussing here Frank Sterling law. So what this law says is this the relationship between the amount of ventricular stretching and the contractile forces and the contractile forces means that within physiological limits increase in EDV will result in the corresponding increase in stroke volume. So in other words sometime it is called more in equals to more out and this was first developed by Ernst H. Sterling based on some of the findings of Otto Frank and now it is being said that this falls under something called Frank Sterling law or Frank Sterling rule which basically says that within the physiological limit the ventricles can expand as more and more contractile forces but more and more I should say stretching is allowed. So they have significant amount of room to do so. So from here let us move on to the next phase of it which is basically another very interesting thing. So that is hard sounds. So whenever we see the doctor says about the hard sounds what really is the hard sounds hard generate 4 kinds of sound and there is a term for this when you see the doctor is using stethoscope to figure out. So hard generate 4 kinds of sounds sound 1, sound 2, sound 3 and sound 4 but generally most of the time we could hear to only 1 sound only 2 kinds of sounds which we could hear is basically something like this if these are the sound waves which are getting generated because of placing of the and this sound waves are generated because of the opening and closing of the valves. So s 1 this one is s 1 this one is s 2 this one is s 3 and this one is s 4. So these 2 sounds are fairly faint you really cannot hear this sound so easily this one is basically l up you hear and then you hear another sound which is called dup. The l up and dup are basically mark the this one mark the ventricular contraction and on the other hand the dup talked about the ventricular filling and the closing of the semilunar valves. So based on this you can even figure out the volume change in the volume. So the maximum volume which is being accommodated in the ventricles so the volume changes maximum volume becomes in the ventricles. So if you look at now summarize what we have touched as of now is that we talked about the contraction system we talked about the conduction system we talked about the irregularity in the conduction system leading to some form of arrhythmia or irregularity which can be cured. So how you get around all these things say for example. So if again back you hear that people are having pacemakers so what exactly pacemaker is all about. So if this is the circuit where you have the a v node and this is moving and this is the per k n j and all other things. So say for example there is some form of a blockage out here say for example there is some blockage or some blockage here or something here. So what will happen the signal will move signal in this case it will move up to this in this case up to this this case it will move faintly up to this and then it will move along this and it will stop here and this will stop here signal will not be able to propagate along these lines. So these are the places which are now in the black they are all devoid of signal there is no signal reaching. So basically the contraction of this is not going to take place or the contraction of this is not going to take place contraction of this is not going to take place how to get around it what is the way what are the different ways. So one way is that either you repair this some way or other you repair this it is just like you know there is a gap in the bridge or there is a breakage and you will again regulate this get the circuit back in place like this. This is one way of doing it but that is not a easy way that is not so that is not something so easy to do what you instead what the doctor does is this they implant a pacemaker out here wherever they know exactly. So what a pacemaker does this is what a pacemaker does it generates certain frequencies certain specific frequencies it generates and those frequencies stimulate these different muscle cells wherever there are cardiac myocytes to pump the blood. So in other what you are doing is that you were replacing the electrical blockage in electrical conduction by introducing a artificial electrical conducting system in the form of a pacemaker this is exactly what you do you introduce another artificial small chip which is being implanted out here and that chip generates a certain kind of frequencies and that frequency is good enough it has to be it has been worked out good enough to you know ensure that all your four chambers keeps on beating in a certain in a sequence same sequence as it is being regulated by the conduction system. So this is the problem of the pacemaker which is taking care of your conduction system pacemaker has nothing to do with your contraction system what about the heart attacks heart attacks are situation when there is something called myocardial infraction what does that mean myocardial infarction or coronary thrombosis these are different pathological condition what is exactly happening. So what is happening in this situation is whenever there is a cardiac arrest or so we talked about the conduction system in the case of heart attacks these contractile elements which I am putting in magenta now gets damage damage in contractile elements. So in other words your elements which are supposed to contract are unable to contract properly and that is a case of a heart attack and these could be diagnosed using bunch of cellular assays like L D H lactate dehydrogenase because these cells secrete certain specific enzymes into the blood then you have serum glutamic oxaloacetic transaminase it is in short it is called S G O T assay then you have creatinine phosphokinase assay C P K assays. So there are whole range of assays which helps you to you know understand that there is a damage in the contractile element. So if I have to summarize what we have discussed in this whole section is we talked about let me go back so we talked about the structure of the heart we talked about why do not I write it down okay. So we talked about the structure of the heart structure of the heart we talked about conduction system we talked about contraction system we talked about ECG or EKG we talked about volume change and we talked about cardiac output and few other things are in there and finally we talked about what is heart attack. So I believe that this much is sufficient for you people to understand that how the heart is exactly functioning and this will help you to you know get a feel about how the system is getting integrated and as we will move further into the nervous system and the hormonal milieu we will come back to the system to talk about how the nervous system is controlling the heart how the hormonal system is controlling the heart and we will be coming back to the excitation contraction coupling apparatus within the cardiac myocytes we will be talking on that also because well while you will be talking about the muscle okay with this I am finishing this section 3 which constitute our heart and from here we will move on to the section 4. So thanks for now.