OK, we'll get started on the heart. My name is Ravi Theogarajan. I'm a cardiac intensivist from Boston Children's. And I've been in the field for about 25 years, and I'm going to summarize what I know in 20 minutes. But what I thought I would do, there are two talks as part of your SCCM board review package. I thought I'd pull out some points that are useful for the exam, as well as for clinical practice. So here are my disclosures, none relevant to this topic. Just a little bit of introduction, congenital heart disease is one of the more common forms of congenital malformations in children. The incidence is about 4 to 10 per 1,000 live births. And if you actually look at the number of children that require care in the ICU, about a third of patients with congenital heart disease require hospitalization and an intervention in infancy. So those are the patients that occupy our beds in our ICU. It's really important to realize that congenital heart disease is often a manifestation of other genetic syndromes, such as patients with DeGeorge, which is 22q11 deletion. And in DeGeorge syndrome, you have a constellation of hypocalcemia, immune deficiency, mental retardation, reduced mental functioning, as well as coronotruncal abnormalities. And coronotruncal abnormalities are usually tetralogy of fallot or truncus arteriosus. So those are associations with DeGeorge syndrome. The reason why it's important to recognize is that in exams, sometimes people may ask, give you a patient with tetralogy of fallot and hypocalcemia, and the question may be what syndrome may be associated with that. Congenital heart disease may also be associated with other non-genetic syndromic abnormalities, such as vactral. And in this abnormality, there's skeletal, gastrointestinal, as well as congenital heart defects, which is usually ventricular septal defects. Diagnosis for congenital heart disease is largely by echocardiography. It's very rare that we need other forms of imaging to define congenital heart disease and define it in a way that your surgeon can actually plan an operation based on an echocardiogram. The echocardiogram is advanced enough that we could just use that to plan an operation or to decide how to manage your patient. Increasingly, we're using CTs and MRIs, and these are largely for operation planning or to look at certain aspects of congenital heart disease. For example, coronary artery anatomy in patients with transposition of the great arteries, where you're going to be repairing the coronaries, or in other coronary abnormalities, you may want a CT. And MRI is largely used mostly for functioning of the heart and also to estimate valve regurgitation. Cardiac catheterization is rarely used for pure diagnostic purposes. And again, you could use cardiac catheterization to define coronary anatomy, but we rarely use it to define anatomy of congenital heart disease. But cardiac catheterization is largely used for interventional purposes, either to correct a defect or to palliate a defect, such as placing a stent in the PDA in a duct-dependent lesion or opening a pulmonary valve in a patient with pulmonary stenosis. Saying that it's as part of boards, there are certain formulas that you all need to remember, and these come from the cardiac catheterization data. And one aspect of formulas that are really important is how to calculate cardiac output. And in most cath labs, we use the Fick principle to calculate cardiac output. And Fick principle is oxygen consumption divided by the AVU to oxygen difference. And so it is VO2 divided by systemic arterial oxygen content minus systemic venous oxygen content. And oxygen content is calculated by hemoglobin times 1.36 times 10 times saturation plus dissolved oxygen. And dissolved oxygen, generally in congenital heart disease, is relatively negligible, and we never use it. And if you do want to use it, you add plus 0.003 times your PaO2. And that gives you systemic output. If you want to calculate how much of output you have from your pulmonary tree, then it is VO2 divided by pulmonary vein saturations. Pulmonary vein saturations are fully saturated blood minus pulmonary artery saturations, which should be the same as your mixed venous oxygen saturation if you didn't have a left-to-right shunt. Another thing that we commonly use in congenital heart disease is estimation of an intracardiac shunt, or a left-to-right shunt, which is usually amount of pulmonary blood flow divided by the amount of systemic blood flow. And if you use the top two equations of QP divided by QS, it then simplifies to peripheral oxygen saturation minus mixed venous oxygen saturations divided by pulmonary vein oxygen saturation minus pulmonary artery oxygen saturations. And we use QP, QS, or shunt fractions to decide how much of pulmonary blood flow, what the magnitude of shunt is, and to plan operations or interventions for your patients. And then finally, the other aspect of calculations that are sometimes important is measurement of resistances. We know that difference in pressure across a tube is a function of flow times resistance equals to change in pressure across fluid flowing across a tube. And this principle is similarly used to calculate systemic vascular resistance, which is mean blood pressure minus CVP divided by QS, which is cardiac output. And in general, normal SVR is 20 to 28. And then we also calculate pulmonary vascular resistance. We use pulmonary vascular resistance as part of planning operations or deciding appropriateness of operations. So that's mean pulmonary artery pressure minus wedge pressure, which is your left-sided pressure, left atrial pressure, divided by QP. And the usual pulmonary vascular resistance is 1 to 3. And I wrote it as WU, which is wood units. And wood units is usually indexed to body surface area. So if you didn't index it, then that's not wood units. But if you indexed it to body surface area, then you would call that wood units. So those are important formulas to remember. These are easy to calculate. And if you should have a question, you should be able to score 100% on those questions, because this is just a calculation. So how do we use QPQS? And this is just two examples of how we use QPQS as a way of estimating shunts. So these are left-to-right shunts across the atrial or the ventricular septum. And this is an example of an atrial septal defect. And if you actually follow oxygen saturations measured by cardiac catheterization, you can see a mixed venous oxygen, or SVC, saturation is 66%. Mixed venous saturation is defined as saturation in the pulmonary arteries in patients without shunts. But in congenital heart disease, we use superior vena cava saturation as equivalent to mixed venous saturation. So if there's a question asking you to calculate a left-to-right shunt, and if you're offered a pulmonary artery saturation and an SVC saturation, so your mixed venous saturation would be your SVC saturation rather than your pulmonary artery saturation. So here, in this example, you can see that the SVC saturation is 66, atrial saturation is 84, RV saturation is 84, pulmonary artery saturation is 88, LV saturation is 99, which is equivalent to pulmonary vein saturation, and then overall systemic saturation is 99. And if you use the formula, systemic oxygen saturation minus mixed venous saturation divided by pulmonary vein saturation minus pulmonary artery saturation, you'll get 99 minus 66 divided by 99 minus 84, and that's 33 divided by 15, which is 2.2. So your left-to-right shunt is a magnitude of 2.2. And the other thing that I wanna point out is that you can see that there's an increase in saturation. In patients with no shunts, your mixed venous saturation, your SVC saturation should be your right atrial saturation, right ventricular saturation, pulmonary artery saturations. If you have a shunt, then you are going to see differences or increased left-to-right shunt. You're gonna see an increase in saturation either in the atrium or the ventricle, depending on where your shunt comes from. So in an atrial septal defect, you'll step up in saturations in your atrium. Similarly, if you look at a ventricular septal defect, you'll step up in saturations in your ventricle. Yeah, there's no step up in the atrium, but there's a step up in your ventricle. So we use cardiac catheterization saturation data to tell us where, to calculate the magnitude of shunt and to also point out where the shunt is so that you can then move forward and plan your operation or other medical management. So that's one example of how we use intracardiac left-to-right shunts. I thought I would choose two congenital heart lesions that are commonly asked for in, or questioned in the boards as a way of illustrating some other aspects of congenital heart disease. And I chose tautology of Fallot and single ventricle congenital heart disease. In tautology of Fallot, which is a really common form of congenital heart disease, there is a ventricular septal defect. We call it a corner ventricular septal defect because the ventricular septal defect in tautology of Fallot is very specifically located between the pulmonary artery and the aorta. So we call it corner ventricular defects. There's obstruction to the right ventricular outflow tract. The aorta overrides the septum and there is hypertrophy of the right ventricle. So those form the four features of tautology of Fallot. So VSD, right ventricular outflow tract obstruction, right ventricular hypertrophy and aortic override. So the physiology in tautology of Fallot is mixed venous blood comes back into the right atrium, goes down the tricuspid valve into the right ventricle and it has two ways to go. One is up the right ventricular outflow tract, which is what it should do. Or in tautology of Fallot, you have a VSD. And because the right ventricular outflow tract is obstructed and there's increased resistance, blood is going to preferentially flow across the VSD into the left heart. And therefore, you have mixing of mixed venous blood, which is desaturated with fully saturated blood that comes back from your pulmonary veins. So therefore, saturation in your ventricle is going to be a feature of how much of blood flows across, how much of desaturated blood flows across the ventricular septal defect into the left side of the heart. The amount of blood that flows across the VSD is determined by the amount of obstruction you have in the right ventricular outflow tract. So if your obstruction is more severe, then you will have more blood flowing from the right ventricle into the left ventricle through the VSD. And therefore, your oxygen saturations are likely to be lower as your right ventricular outflow tract obstruction increases. And right ventricular outflow tract obstruction could be static, which is it is anatomically obstructed, or there could be a dynamic component to it. And dynamic component is usually related to spasm of the infundibular portion of the right ventricular outflow tract. And the infundibulum is a connection between the right ventricle into the pulmonary artery, and then you could have spasm of the infundibulum that may actually worsen right ventricular outflow tract obstruction and cause increased shunting across the VSD into the left side of the heart. And that's typical feature of TET spells. And TET spell is an acute increase in right ventricular outflow tract obstruction that leads to cyanosis related to increased flow across the VSD into the left side of the heart. So that causes you to have acute severe cyanosis that's usually increased right ventricular outflow tract obstruction. And therefore, management strategies for a TET spell are largely relieving that dynamic obstruction in the right ventricular outflow tract. There's one other reason why you could become acutely desaturated in patients with Tetralogy of Fallot, that is decrease in systemic vascular resistance. If you decrease systemic vascular resistance, such as a patient with Tetralogy of Fallot has a fever, or you gave them an anesthetic, commonly done for doing an echocardiogram so that you could define coronary anatomy where you want your patient to be really still. And if you reduce stress response or you cause vasodilation from your anesthetic, then you're going to increase the right to left shunt across the VSD and cause the patient to have a TET spell or be desaturated. The management of TET spells is really, most often occurs when patients are agitated. So you want to comfort them. You can give them some oxygen. You could certainly use morphine as a way of relieving pain. And if you have fever, it's really important to treat fever and normalize temperature. And then the knee chest position is pushing the knees into your abdomen. And that can sometimes cause more agitation. However, what it does physiologically is it increases systemic vascular resistance and therefore restricts right to left shunt across the VSD. So that's kind of Tetralogy of Fallot with Tetralogy of Fallot TET spells and management of TET spells. The operative or definitive treatment for Tetralogy of Fallot is repairing the defect. And that includes opening up the right ventricular outflow tract, using an incision across the outflow tract, across the annulus of the pulmonary artery, and then using a patch to open up the right ventricular outflow tract, closing the VSD. So that is repair of Tetralogy of Fallot. We generally repair Tetralogy of Fallot, at least in modern times, within six months. Six months is kind of the maximum limit. We'll allow patients to go with Tetralogy of Fallot. Or if they have a TET spell, a single TET spell is enough to proceed forward with an operation. So usual indications are six months of age in a patient who is asymptomatic, or a TET spell gets you a repair of Tetralogy of Fallot. I'm gonna move on to single ventricle congenital heart disease. This is commonly asked in boards. Management of single ventricle congenital heart disease, how do you balance pulmonary and systemic blood flow? Those are common questions that are asked. So single ventricle congenital heart disease is defined as a heart that has a single pumping chamber, and may or may not have outflow tract, which is pulmonary or systemic outflow tract obstruction. But the most important feature here is you have a single pumping chamber. The other chamber is not big enough to handle a whole cardiac output. So single pumping chamber, with or without outflow tract obstruction. If you have outflow tract obstruction, then that single ventricle lesion becomes duct dependent, either because you have pulmonary outflow tract where you have to maintain pulmonary blood flow using adductors, or systemic outflow where you have to maintain your systemic flow using adductors. I'm gonna use the example of hyperplastic left heart syndrome because that's the most commonly asked, and what interests most people is hyperplastic left heart syndrome. So hyperplastic left heart syndrome is a constellation of left heart hyperplasia, where you can have hyperplasia of the left ventricle, you can have hyperplasia of the mitral valve, and when I say hyperplasia, the structure's small enough now to be able to accommodate a full cardiac output. So it may be moderately hyperplastic, but we would still treat that as hyperplastic left heart syndrome. So hyperplasia of the mitral valve, or atresia of the mitral valve, where there's no flow across the mitral valve, hyperplasia of the aorta, aortic valve, and ascending aorta, or atresia of the ascending aorta and the aortic valve. In hyperplastic left heart syndrome, systemic venous blood comes back into the right atrium, pulmonary venous blood comes back into the left atrium, and they commonly mix in the atrial atrium, and then that blood, commonly mixed blood, is then, goes down into the right ventricle through the tricuspid valve, and then is ejected through the pulmonary arteries. And once the blood gets to the pulmonary arteries, there's two ways to go. One is across the ductus into the systemic outflow tract, or back into the lungs through the pulmonary arteries. And the whole management of this circulation depends on how much of systemic and pulmonary blood flow, and how you're gonna balance that circulation. So this is a circulation in parallel. So there's a single pumping chamber, pumping to your pulmonary circulation and systemic circulation. So it's a circulation in parallel, and therefore you have to balance pulmonary and systemic blood flow. These lesions, as you know, are duct-dependent. If the ductus closes, then you're gonna present in cardiogenic shock because you don't have systemic output. Like I previously said, SVR-PVR balance. The way you balance pulmonary and systemic blood flow is balancing resistances. If your SVR is high, more blood will flow into your lungs. If your PVR is low, or your SVR is low, there'll be more blood flowing into your systemic artery. So really balancing systemic pulmonary vascular resistance is really the principles of how we manage children with parallel circulations. One last aspect of hyperplastic left heart syndrome that's important, although it's important for a cardiologist, perhaps not for intensives, although we get to manage these patients who are really ill, is if you have obstruction in the atrial septum. If you don't have a common atrium, where left atrial and right atrial blood can mix easily, then those patients present acutely. If you have obstruction, or if you have no communication at the atrial level, pulmonary venous blood that comes back into the left atrium has nowhere to go. So that left atrial pressure's gonna get higher and higher, and that's gonna be reflected in your lungs. So these patients often present with severe hypoxia soon after birth, and low cardiac output. This is an emergency. You have to go to the cath lab and open up the atrial septum or consider an operative procedure to rescue that patient. Many of these patients have had their atrial septum obstructed in utero. So that condition has been there for a long period of time, and therefore they have significant pulmonary vascular disease, just like somebody with total anomalous pulmonary venous return that's obstructed have. And these are the highest risk type of hypoplasty we manage. Many of them end up dying because we just don't have good treatment options for them. So how do you manage QPQS? Just applying the same formula of QPQS that we learned from having a patient with two ventricle and assessing a shunt. It's the same principle that we use here. So QPQS is balanced. I'm actually going to slip, next talk is also by me, so I'm gonna use some of this time to, my 20 minutes is gonna go to 30 minutes, I think. Yeah, all right. Okay, so we use QPQS to estimate how much of pulmonary and systemic blood flow there is, and we use the same formula, QPQS. So systemic arterial oxygen saturation minus systemic venous oxygen saturation divided by pulmonary vein saturation minus pulmonary artery saturation. The only difference here is that systemic vein saturation, so the saturation's coming back into the SVC, the blood that's going into, sorry, the saturation in your pulmonary artery is the same saturation as in your aorta. So the difference is that, and therefore, your QPQS is peripheral oxygen saturation, which is 80 minus 60 in this case, divided by pulmonary vein saturation, which could be 100%. If you have to assume pulmonary vein saturations in these patients, it's often 100%. If you have somebody with normal-looking lungs on chest X-ray, minus 60, which is your mixed venous oxygen saturation. So in this example, if your peripheral saturations are 80% and your mixed venous saturation is 60, then your QPQS is 80 minus 60 divided by 100 minus 80, which is a QPQS of one-to-one. So it's systemic arterial oxygen saturation minus systemic venous oxygen saturation. Here in this example, it's 80, which is your peripheral oxygen saturation minus your mixed venous saturation, which is 60, divided by pulmonary vein saturation, which we're assuming to be 100, minus pulmonary artery saturation, which is the same as your systemic venous saturation because it's commonly mixed blood that's going into your pulmonary artery and going into your systemic circulation. If your oxygen saturation, systemic oxygen saturation is 90%, the only time that can happen is if you have more pulmonary blood flow. So the higher your oxygen saturations, the more pulmonary blood flow and more unbalanced your QPQS is. For example, if your systemic oxygen saturation is 90% and if your mixed venous saturation still stays 60, then it's 90 minus 60 divided by 100 minus 90, which is a QPQS of three to one. And that usually presents in cardiogenic shock. And what we're really trying to do with the circulation is to get as close to one to one as possible. So we are really looking at modifying systemic vascular resistance to allow more systemic blood flow and to manage balance the circulation. Another aspect of QPQS in a congenital heart disease with parallel circulations, your systemic oxygen saturation gives you a good idea as to what your QPQS is because the higher your oxygen saturations that you're measuring in your peripheral oximetry reflects how much of blood flow you have. So the higher it is, the more your QPQS. So you don't really need really complicated measurements to tell you what your QPQS is. You could just use peripheral oxygen saturations and physical exam to kind of determine where you are with single ventricle parallel circulations. The management of hyperplastic left heart syndrome is to getting a parallel circulation to a circulation in series. But we have a circulation, normal human beings have a circulation in series where right ventricular output goes up and your lungs comes back and fills the left side and that becomes your systemic heart. So that circulation's in series. And we wanna convert this single chamber that's pumping to two circulations to a circulation in series. And we do that through an iterative process of starting with the stage one palliation which is really replicating the parallel circulations but without dependence on the ductus to changing it to a glen circulation where you're really starting to bring your systemic, separate your systemic venous from your systemic arterial blood flow using anastomosis of the SVC into the pulmonary arteries and then eventually separating the venous and the arterial circulations by creating what's called a Fontan procedure where both the IVC and the SVC blood flows are then directly anastomosed into your pulmonary arteries and go into your lungs. And oxygenated blood from your lungs then comes back into your systemic ventricle and then is ejected out. So we do this through a series of operations to help us separate the circulations which are in parallel to circulations that are in series. Patients with single ventricle, single ventricle palliation after the stage one which is a Norwood operation or the Sano operation, the principles of management are the same as you would in a patient who's duct dependent. So you're really balancing QPQS, supporting the function of the heart, of the ventricle and really reducing SVR. Early on, we used to increase PVR and not worry too much about SVR and that's how these circulations were managed. But we've now changed what we do to really managing or reducing SVR to allow blood to flow into the systemic circulation then work with the PVR. What happens when you manipulate or increase PVR is that you find yourself in a situation where both SVR and PVR are elevated and therefore you're increasing workload to the single ventricle. So we've kind of changed tune a little bit to help us do better with this patient population. Front-end circulation is a little bit more complex and it really requires you to think through multiple aspects of flow and how you would optimize the circulation. So in a front-end circulation, the SVC and the IVC are directly in osmosis of the pulmonary arteries. So you don't have a ventricle pumping blood through the pulmonary arteries into your lungs and therefore blood is flowing passively into the lungs. And then blood that flows into your lungs gets oxygenated and then comes back into the left atrium and then is pumped by the ventricle into the systemic circulation. Couple of things about the front-end circulation that are important are that because you don't have a pumping chamber, blood flow into your lungs is a function of preload and venous capacitance. If your venous capacitance is decreased, then you have more blood flowing into your lungs. If your venous capacitance is increased, that means more blood stays in your venous circulation and cannot reach your lungs. So that's a really important aspect. Often when you do your front-end operations first, patients don't have, patients have large venous capacitance until they develop muscle in their veins to push blood into the pulmonary arteries. Any obstruction, anatomical obstruction to the main pulmonary arteries and any elevation of pulmonary vascular resistance is a problem because this passively flowing blood is not going to flow into your lungs. And what flows into your lungs is your cardiac output. So if you don't have enough blood flowing into your lungs, then you're not gonna have enough blood coming back to your systemic ventricle. And then finally, you have to have a systemic ventricle that works well. If you have a systemic ventricle that's dysfunctional, then the downstream pressure is really elevated and this whole circuit then falls apart. So for a front-end circulation, you have to have adequate preload. We usually use CVP to help us decide that. We want your CVP somewhere in the 12 to 15 range. You want your lungs to be as healthy as possible. You want your pulmonary vascular resistance to be as low as possible. And these patients don't tolerate positive pressure ventilation because you're increasing your interthoracic pressure. So you wanna get these patients extubated as quickly as you can. And then you want your left-sided heart to work well. So if you have elevated end-diastolic pressure, if you have any obstruction to flow across the aorta, then those patients don't do very well because their front-end pressure will go up. One way of offsetting some of this, because we're not doing the bestest front-ends, we're usually doing high-risk front-ends these days, is to use a fenestration. And the fenestration is a communication between the venous limb of the front-end and the left atrium. And this is placed operatively in the operating room. And what this does is that it offsets some of the blue blood that comes back into the venous circulation into your left atrium. And therefore, your oxygen saturations overall decrease, but you're able to maintain cardiac output because you're not dependent all the blood flowing into your lungs coming back into your heart. And therefore, that's kind of a way that we have improvised the circulation to be able to manage these patients better. So post-operative front-end management is really ensuring adequate preload. A dry front-end is a dead front-end. That's something that we say in RICUs all the time. You want early extubation. You want to ensure that there is open fenestration. If you have a closed fenestration, and unless your front-end is perfect, that'll be a major issue. Your cardiac output will be low, and you may want to consider how you might want to open that fenestration again. It's not uncommon for fenestrations to clot after they come back from the operating room. You want to ventilate. If you have to ventilate a front-end, use the lowest mean airway pressure possible. Inhaled nitric oxide could be used if your pulmonary vascular resistance is elevated. And then it's really important to ensure that you're on sinus rhythm, because if you're asynchronous, if you have atrial and ventricular contractions that are asynchronous, then your atrium is going to contract against a closed mitral valve or a tricuspid valve, depending on what type of anatomy you have, and that will raise the left atrial pressure. And if your left atrial pressure goes up, then the entire front-end circulation is obstructed. So it's really important to have AV synchrony, and it's really important to offload, reduce these patients, so that you can improve the efficiency of your front-end circulation. I was going to talk a little bit about temporary cardiac output and pressure-volume loops, but I'm going to go on to the next one. Yeah.

congenital heart disease

tetralogy of Fallot

single ventricle defects

hypoplastic left heart syndrome

cardiac catheterization

echocardiography

DeGeorge syndrome