Hi, thanks for having me. I know lectures after 5 p.m. can be tough after a long day, so I appreciate the opportunity to speak. I like to set forth some learning objectives for every lecture, more of an outline so that you know what to expect out of the next hour. The scope of this talk was not such that I could cover conduction disease, pacing, device management, and sudden cardiac death risk in the ACHD population. So what I've tried to do is focus it down a bit, and given that this is targeted for fellows, I've tried to focus this a little bit on the core EP concepts of arrhythmia substrate, anatomy, and ablation. So the learning objectives are there, and hopefully you'll feel like we've met them by the end of this period. So one of my mentors in fellowship used to say it's all about perspective, and I think that's particularly true as we try to understand the burgeoning scope of this field that is adult congenital heart disease. I think if you spend some time listening to congenital cardiologists who are well established, like Jane Neuberger at the AHA a couple of years ago, what you'll end up hearing over and over is that the ACHD population is a rapidly expanding population, and in many ways is the population that will require the most care in the coming decades. And unfortunately, or maybe fortunately, for those of you still trying to decide exactly what your specific interests will include, there's currently a dearth of providers whose practice is dedicated to this population. What we know is that over the last three decades, we've seen major improvements in the preoperative, surgical, and long-term management of children undergoing congenital cardiac surgery that has resulted in an ever-expanding population of young adults with congenital heart disease. Fortunately, when it comes to the management of their heart rhythm issues, I think or hope what this talk will at least start to prove to you is that, in fact, adults with congenital heart disease are much more like the adult patients that you all are probably taking care of in your clinics and EP labs than you realize. This is a paper that was published over 10 years ago now in circulation, but it postulated that atrial arrhythmias increase with age and impair health outcomes in the growing adult congenital population. They conducted a population-based analysis, including prevalence, lifetime risk, morbidity, and mortality associated with atrial arrhythmias in adults with congenital heart disease between 1983 and 2005. They looked at about 38,000 adults with congenital heart disease, and they demonstrated that about 5,800 of them had atrial arrhythmias. Overall, what they found was that the 20-year risk of developing atrial tachycardia is 7% in a 20-year-old patient and 38% in a 50-year-old patient, such that a 20-year-old patient with ACHD has the same arrhythmia risk as a 55-year-old within the normal population. What was most concerning about this study, however, was the hazard ratio of any adverse events in those patients with atrial arrhythmias compared to those without was 2.5, as you can see right here. There was a near 50% increase in mortality, more than double the risk of morbidity, specifically stroke and heart failure, and three times the risk of cardiac intervention. If approximately 15% of adults with congenital heart disease have atrial arrhythmias, and that risk increases steadily with age, you come to this idea that you've probably heard before in the pediatric and congenital population of young patients with aged hearts. As adult electrophysiologists, you're going to know this cycle better than most pediatric providers, but atrial arrhythmias lead to atrial hypertension, which leads to atrial stretch and volume overloading, and this leads to atrial remodeling and increased substrate for atrial arrhythmias, and this vicious cycle continues. Furthermore, we know that atrial arrhythmias result in ventricular dysfunction, we worry about thrombus, we worry about antiarrhythmic therapies and their side effects, and then we think about inpatient hospital admissions for medication titration and for management of those medications. Furthermore, we know that atrial arrhythmias result in ventricular dysfunction, we worry about thrombus, we worry about antiarrhythmic therapies and their side effects, and then we think about inpatient hospital admissions for medication titration and for management of those arrhythmias. In the congenital heart disease population, these schematics are the same in terms of things that affect or lead to arrhythmias, except for, as we've sort of discussed, they occur at an earlier age and the risk of ventricular dysfunction is higher in certain subsets of the repaired congenital heart disease population. So what contributes to this increased risk of arrhythmias? The short answer is that it is inevitably more than one thing. However, we've postulated, and others smarter than myself have postulated, that it's the combination of long-term hemodynamic stress coupled with repeated surgical intervention imposed in a variety of congenital cardiac lesions that creates an ideal environment for the genesis of varying tachycardias. Specifically, re-entrant circuits dependent on central fixed obstacles to conduction and variable slights of slow conduction or functional block. You all know this diagram. You probably dream about it in your sleep at this point, but it's the wavelength theory for re-entry. We basically know that you need a central obstacle to conduction, you need a circuit of sufficient length, you need an overall conduction velocity plus or minus the zone of slowed conduction and maintaining an excitable gap, and you need a refractory period that's shorter than the time to complete the circuit. So you don't need to complete a single circuit. Not new information to any of you. In adults with congenital heart disease, there are additional factors that enable the setup of these circuits, sometimes earlier than you would otherwise see them in a structurally normal heart. So, tricuspid valve and atriotomy scars form central obstacles to conduction. You have chronic right atrial dilatation that allows for right atrial stretch and alteration of right atrial conduction velocities and refractoriness. And our surgeons, fortunately, provide excellent scar sites for zones of slow conduction. But how does the mechanism of atrial dilation contribute to what we know as macro-re-entry tachycardia? So, the mechanism by which atrial dilation or dilatation may promote typical atrial flutter has been studied in patients with unrepaired ASDs with no prior arrhythmic history that may have facilitated atrial remodeling. Chronic atrial dilation led to conduction delay at the crista, as defined by the magnitude and the delay between double potentials recorded at this site in this paper seen here on the left. Additionally, there was a trend towards increased atrial effective refractory periods and sinus node dysfunction, but no changes in the conduction velocity of the right atrial free wall. These findings in this study weren't present in age-matched controls. And subsequently, despite ASD closure, conduction block at the crista and atrial dilation were still present at follow-up evaluation, suggesting that persistent atrial dilation and conduction delay at the crista support atrial flutter even after ASD closure. Similarly, electrophysiologic changes have been documented in the left atrium of patients with ASDs, including chamber dilation and electrical scar, with widespread changes in conduction velocity characterized by fractionated EGMs and double potentials similar to the RA with an increase in the effective refractory period. This remodeling in this paper published in 2009 was associated with an increased propensity to atrial fibrillation. So I'm just going to spend a few minutes because I think you can spend the better part of a full first year of a pediatric cardiology fellowship in the anatomy and pathology labs trying to understand the complexities and the intricacies of congenital heart disease anatomy. The scope of this talk is not by any means intended to make you an expert of congenital heart disease or segmental anatomy. What we basically want, or what I basically want you to try to understand, is a few of the basic anatomic substrates that will inevitably cross into your hospitals, clinics, and EP labs, and to try to encourage you to think about things, both from the anatomic perspective, but also functionally, sort of like we do as biventricular repairs or univentricular repairs or single ventricle repairs. I'm going to encourage you to break things down into sort of three major groups for the purposes of this talk. Simple or isolated defects like ASDs, VSDs, and Epstein's, biventricular circulation, and then single ventricle circulation. For those who are really interested, there's a long list of classifications of congenital heart disease complexity that's been established by the PACE's HRS working group on adult congenital heart disease, and all of that can be found in their consensus statement if you're interested. When we think about anatomy 101, sort of the crash course to congenital heart disease as I imagine it, I'm going to talk about these major groups, septal defects, Epstein's anomaly, Tetralogy of Fallot, mustard and sending repairs, and then single ventricle palliation. I'm not going to spend too much time on ASDs and VSDs because functionally you know what they are and you see them probably as much as we do. But in terms of Epstein's anomaly, eponymously described in 1866, Epstein's anomaly is characterized by failure of the posterior and septal leaflets of the tricuspid valve to delaminate from the underlying myocardium to which they're adherent. And this creates apical displacement of the leaflets and an atrialized portion of the right ventricle. The anterior leaflet is often enlarged and fenestrated and failure of valve leaflet coaptation leads to varying degrees of tricuspid regurgitation with dilation of the true tricuspid valve annulus and right atrium, facilitating typical atrial flutter, atrial fibrillation, and focal atrial tachycardia. In addition, accessory pathways are present in the literature in as wide a spectrum as 6 to 36% of patients who present with Epstein's. So important for people to know that there is that predilection for accessory pathways in patients who have Epstein's anomaly. In addition, if you remember back to the initial numbers, the documented prevalence of atrial tachycardias in ACHD as a whole is about 15%. But it's higher in what are considered more complex congenital lesions. And that includes things like Epstein's with a stated prevalence of about 33%. These are two atrial, excuse me, these are two electrocardiograms from two patients with Epstein's. On the left is a 40-year-old patient who had undergone a prior tricuspid valve replacement who presented with palpitations. And the ECG is consistent, if you can see here. With typical atrial flutter around the tricuspid valve via the cabotricuspid isthmus. Note the relative isoelectric interval between discrete atrial flutter waves and a cycle length of greater than 200, which is probably a little bit different than you're used to seeing in a normal atrial flutter patient in a non-congenital heart disease patient. This second ECG, which you can see here, is from a 38-year-old male who presented with no history of prior surgery, came in with mild lethargy and exercise tolerance, and an ECG demonstrated appearance of what looks to be like pre-excited atrial flutter with inverted flutter waves in the AVL and best seen probably here in Leeds. And this is a picture from 2002. I hope this will work. So this is just a quick echo picture of this septal leaflet that is displaced, representing an ebstinoid picture. So this is a picture of a septal leaflet to Tetralogy of Fallot. Functionally, this is a two-ventricle circulation. They have four major parts of their congenital heart disease. They have right ventricular hypertrophy, they have a VSD, they have pulmonary stenosis, and their aortas are slightly displaced. These aortas usually consist of patching the pulmonary stenosis to create a relatively normal-sized pulmonary artery and closing the VSD. But functionally, patients with Tetralogy have two-ventricle circulation. In transposition physiology, which you can see here, patients are born effectively with parallel circulations, and this is specifically what we call delooped transposition. So right atrium to right ventricle, right ventricle out to the aorta. Not a fantastic setup for optimal oxygen delivery. We used to perform something called the mustard or senning repair, which is basically an atrial-level baffle, which tries to direct the blue blood to the left ventricle and then out to the pulmonary arteries to be recirculated, and then comes back to the right ventricle, making the RV or systemic ventricle, which over time is not as good. It's not fantastic, and that goes systemically to your aorta. The atrial switch or the mustard senning was the surgical strategy of choice for many years for transposition prior to the introduction of what you can see here on the far right, which is the arterial switch. But importantly, the atrial switch is still used as part of the double switch for congenitally corrected transposition. When we think about the estimates of arrhythmia burden in transposition physiology, the quoted numbers are around 28%. Finally, just in our list of four anatomical substrates that we're going to think about through this lecture, single ventricle palliation. Functionally, there are many congenital heart abnormalities that will be palliated down the single ventricle pathway. We'll spend some time in a bit talking about the evolution of the Fontan, but functionally, with only one functioning ventricle, you need a way to get blood to your lungs passively and to your body actively, and this occurs in a staged approach. Hopefully, by the time these patients end up in your practice, they'll be at the Fontan stage, so this is really the anatomy that you'll need to sort of commit to your brain. But we'll talk a little bit more about the Fontan palliation and how we've gotten to this point, because it is important to understand the stages through which the Fontan has gone through over the past 30 years in order to understand the arrhythmia burden that we see now in this population specifically. In terms of Fontan circulations, they are predisposed also to significant atrial arrhythmia burden. The publisher quoted number for them is about 24.4% as compared to the general 15% in the CHD population. Arrhythmia mechanisms are highly varied in the adult congenital heart disease population. Classically, these lesions are associated with macro-reentrant atrial tachycardias, using sites of fixed and functional conduction block as central obstacles and narrow channels of viable but slowly conducting myocardium to ensure the reentrant wave front is always approaching the patient. Increasingly, however, other mechanisms have been recognized, including focal atrial tachycardias and common arrhythmias, things that you see all the time, such as AVNRT, which sometimes due to anatomic and electrophysiologic remodeling, can look different in terms of intracardiac activation patterns from that seen in structurally normal hearts. This figure is also drawn from the PACE's HRS consensus statement on arrhythmias in the ACHD population. They basically broke down congenital heart disease into levels of complexity, just like we've been discussing, and then they looked at the risk estimates for arrhythmias dependent on that level of complexity. We're not going to cover this in detail today, but what you can see is some patients, D-loop transposition, L-loop transposition, single ventricles, are at much higher risk in terms of arrhythmias over time than those simple, less complex congenital heart lesions. Okay, so you know you have many patients with ACHD, and the risk of these patients having arrhythmias is pretty high. We've tried to sort of talk a little bit about that as a crash course. We've given a little bit of a crash course in anatomy, but I'm going to talk to you a little bit about actual cases, because I think those tend to be the most helpful for people in terms of bringing home or solidifying these concepts. One thing to know about going into the evaluation of ACHD patients with arrhythmias is that there's a lot of information out there. One thing to know about going into the evaluation of ACHD patients with arrhythmias is that these arrhythmias can look slightly different initially than the majority of structurally normal hearts who will walk through your doors. For example, this is an electrocardiogram of a patient who is in what we found out to be typically atrial flutter. But this definitely looks like a slightly different morphology than you're probably used to seeing, and often the cycle lengths can be much slower. So that typical sawtooth pattern, you may be able to expose with different maneuvers, but the baseline ECGs may look quite different because of their underlying congenital heart disease. All right, so the first case involves a 48-year-old female who had a VSD closure at age four, and this was followed by repair of an unroofed coronary sinus at age 38. So effectively, what that means is that she had right atrial and septal incisions with extensive cortex graft from the proximal CS up to the mouth of the left atrial appendage. When we had her vagal down, this is what was elicited, and the diagnosis of atrial flutter was made. She underwent a cardioversion at her request, and then not surprisingly, five months later, showed back up in the ER in the same arrhythmia. So at that point, we brought her to the EP lab. These are intracardiac signals, which you all are very familiar with, and your RAO and LAO views are on the far right. So I'm not sure what your standard approach for a flutter case in the adult world would be, but where I was trained, we would do this as a standard two-catheter study in somebody who has a biventricular circulation. So they went straight up and put the MAP catheter right on the cabotricuspid isthmus, and what you can see here is they demonstrated concealed entrainment from the CTI with the post-facing interval equal to the total cycle length, and the MAP stim to P wave equal to the MAP EGM to P wave. They found these lovely low-amplitude fractionated signals at the CTI, and with an irrigated catheter, which I'm sure you all use regularly as well, started a CTI line as you all would do in the same way, and had termination on the third lesion, which you can see there. Bidirectional block was confirmed at the end of the case, which is, I am sure, something that you all do as well, and repeat testing didn't demonstrate any inducible arrhythmias with an aggressive pacing strategy of triple atrial extrastimulus and isoproteranol. So case two, 53-year-old female with Tetralogy of Fallot, who presented to clinic and was found to have this EKG. Sorry, I blew up a few strips for you. She was asymptomatic with preserved exercise intolerance, and her right ventricular end diastolic volume was large, so about 170 mLs. We usually use a cutoff of 160 is sort of in the larger span. I don't know that you can actually talk, but if you were going to make a diagnosis based on this, based on all the things we've been talking about, she came to the lab after her diagnosis of atrial flutter, had ablation of typical atrial flutter at the CTI, and then, unfortunately, had recurrence. She had recurrence three weeks later, just about a month later when she came for her follow-up visit. So we brought her back to the lab, and what you can see here, I hope these are big enough so that you can see, but four surface leads are displayed for you at the top with intracardiac electrograms from the mapping catheter, with the distal bipolar catheter on the CTI, and the quadrupolar reference catheter in the CS. Panel A was her first study where she had typical atrial flutter that entrained to the cabotricuspid isthmus, and she had a CTI line performed. What you can see in the block B here is that a second study was performed. This is her CARDO map, and reconstruction of her right atrium shown in figure B, this is shown with a chamber viewed from the right lateral projection, just to orient you, and the red denotes here the earliest and the purple the latest site of activation referenced to a stable catheter in the CS. Her clinical tachycardia was identified as macro-reentrant atrial tachycardia, with a site of slow conduction characterized by prolonged low amplitude EGM, which you can see here circled at the lower crista terminalis, which terminated repeatedly with catheter pressure, and ultimately was successfully ablated. Unfortunately, with repeated programmed atrial stimulation, further tachycardia was induced in Panel C, and what you can see here is this sort of centrifugal activation coming from close to the CS os, as displayed in the RA reconstruction seen from the left anterior oblique view, and on termination of ventricular pacing, I hope you can see here, that she has this AAV return sequence, confirming this to be a focal atrial tachycardia that was also successfully ablated. So, in the tetralogy population and in the congenital heart disease population, the idea of finding multiple tachycardia substrates is something to always consider in these patients, and I think it's probably your practice, as it is our practice, to do a significant amount of testing after an ablation to ensure that there's nothing else inducible. But particularly in the adult congenital population, that becomes even more important, and this is a really nice example of that, I think. That's just the block, bidirectional block, being confirmed. All right. Moving on to single ventricles, which, to be totally honest, could be an entire lecture series unto itself, but functionally, if you have the general picture of single ventricle palliation here, so this is the fontan, which is what you're ultimately probably going to see the most of for adults that are coming over to the adult side or adult hospitals. What you see is, historically, the fontan procedure has a bit of a varied course. So, this is Francis Fontan. Unfortunately, he passed away two years ago. He was a French cardiologist and cardiothoracic surgeon who pioneered the fontan procedure. His initial attempts on the fontan procedure on dogs were all unsuccessful, and all of his experimental animals ended up dying within a few hours following the procedure. He ultimately successfully was able to perform the fontan palliation on a young woman with tricuspid atresia in 1968, carrying out what would later be known as the fontan procedure. The operation was completed on a patient in 1970 as a second attempt, and it was ultimately published for the first time in the journal Thorax in 1971, and this is taken from that journal. Interestingly, he was clearly an incredibly smart and creative and thoughtful man, but there was a commentary, even as early as 1971, that the unpredictable element for these patients was the hemodynamic consequence of an event, of an eventual atrial arrhythmia, on which he was quite certain there would be at some point. And he was absolutely right. So, I'm taking you back a little bit, but since its inception, the fontan procedure has had several refinements, some of which were more successful than others. There are a very few number of patients, you may never see them, who have what's called an atrial pulmonary fontan. That's this picture here, sort of simplified, where basically you connect the right atrium directly to the pulmonary arteries. And you can imagine with that, what you get is this massive atrial dilation. What we know about the atrial pulmonary fontan is that they have multiple reentrant arrhythmia circuits. They have a constantly evolving substrate as that atrium dilates progressively over time, and they have a really high recurrence rate post ablation. In fact, before my time here, we were lucky enough to have both Dr. Barbara Diehl and Dr. Sabrina Cho, who sort of were instrumental in doing fontan conversions here in patients who had these massive atrial pulmonary fontans. The experiences here and at other centers have involved the fontan conversions for these large atrial pulmonary fontans to the more accepted now lateral tunnel or extracardiac fontans, or otherwise in other centers known as TCPCs, which stands for Total Caval Pulmonary Connection. The goal of the transition to the lateral tunnel or extracardiac fontan was to reduce the amount of atrial myocardium that was exposed to pulmonary vascular resistance and to therefore reduce specifically the arrhythmia burden. In the newer lateral tunnel or extracardiac fontans, otherwise known as TCPCs, what we know is that these patients still have atrial arrhythmias, but they often have atrial flutter, which is sometimes referred to in congenital literature as IART or intraatrial reentrant tachycardia. They tend to have slightly simpler arrhythmias than we're seeing in those old atrial pulmonary fontans, but these patients are also predisposed to atrial fibrillation. Ostensibly, people felt like when the transition to extracardiac and lateral tunnel fontans occurred that the outcomes long-term were better. In 2007, Broussard's group looked at 305 patients between the years 1980 and 2000 who underwent the fontan procedure, and what you can see here is that the mortality was about 3% total over the course of that study time. But interestingly, there were no deaths after 1990, which is when people really started performing with regularity, the lateral tunnels and the extracardiacs. Independent risk factors for mortality were preoperative elevated pulmonary artery pressures, as you can imagine, and common AV valve regurgitation, which is very problematic in single ventricle physiology. The 15-year survival in this study after atrial pulmonary connection was 81% versus 94% for the lateral tunnel fontans. So not only did undergoing a fontan modification independently decrease the risk or occurrence of arrhythmias in these patients, the 15-year freedom from ventricular tachycardia, which we're not going to talk about in this lecture, but it's also an important arrhythmia for these patients, was 61% for the atrial pulmonary fontans versus 87% for the lateral tunnel fontans. Most importantly, however, though, I think if you look here, what you see is after they switched to extracardiac conduits, there was no deaths nor severe fontan failures in the early follow-up period. So what they determined, or what they ultimately decided, was that patients with lateral tunnel or extracardiac fontans experienced less arrhythmia burden and were more likely to have fontan failure, which is a conversation for another day, postponed. And ultimately, these patients did much, much better. So when we think about the EP experience with fontans, when we think about early arrhythmia mapping and ablation, this is well before my time, but the people who trained me, the Ed Walsh's and the John Triedman's of the world, who've been doing this for 30 years, made sure that we had a high appreciation for all the things that we have and all the tools that we have in the EP lab now to help us map and successfully ablate these patients. But this was definitely an uphill battle for those people who started many, many years ago. So as you all know, in about 1990, we're the first RF ablations of accessory pathways. In the early 90s, we then started, not I say we, but really others, started mapping of arrhythmia substrates and congenital heart disease. And as you can imagine, these were extremely frustrating and complicated to do. And as you can imagine, these were extremely frustrating and complex cases. You had these dilated, scarred, massive atria with limited contact catheters. You were using fluoro only, that was quite two dimensional, and you often had multiple circuits. So the success rate was low, the recurrence rate was high, and I'm sure the frustration level was also high. But things got better. So we got electroanatomic mapping and systems like CARDO came along, and suddenly we had contact mapping, an annotation of activation and voltage maps. And we overlaid this new data on top of the anatomic and electrophysiologic knowledge that the giants in pediatric EP had spent years accruing. So just as an example, in this 2001 study, Jackman and Al looked at 16 patients with atrial tachycardia after surgical repair of congenital heart disease. There were six patients with atrial septal defects, four with Tetralogy, and six with Fontan's. They looked at electroanatomic right atrial maps that were obtained during 15 macro-reentrant atrial arrhythmias in 13 patients, one focal atrial tachycardia, and one during an atrial pacing study. What they subsequently found was these large areas of low bipolar voltage, less than 0.5 millivolts, and that involved most of the free wall, as you can see in that picture. And in all patients contained two to seven dense scars or lines of double potential, forming 29 narrow channels between the scars in pretty much every patient, but one. All 15 of these macro-reentrant atrial arrhythmias were propagated through these narrow channels, and ablation of those channels ultimately eliminated all 15 of those atrial tachycardias with between one and three micro-reentrant atrial arrhythmias, and that's what we're seeing here in this study. They surmised, based on this, that macro-reentrant tachycardia, after surgical repair of congenital heart disease, requires a large area of low voltage and greater than or equal to two scars forming narrow channels, and that if these could successfully eliminate all 15 of those atrial tachycardias, they would eliminate all 15 of those micro-reentrant atrial arrhythmias, and that's what we're seeing here in this study. They surmised, based on this, that macro-reentrant tachycardia, after surgical repair of congenital heart disease, requires a large area of low voltage and greater than or equal to two scars forming narrow channels, and that if these could successfully be eliminated, you can effectively ablate those tachycardias, which these are not new themes, they're just the same themes that you see in your own patients, they are just manifested much earlier in our patients, and sometimes in slightly different locations based on what we're seeing here. So with new technology and new experiences, people started to try to bring these more complex congenital patients to the EP lab with increasing frequency. The Boston Group published a relatively large series on arrhythmias in patients with Fontan or TCPCs. They looked at 57 procedures performed on 52 patients between March of 2006 and March of 2012 who underwent EP study. They looked at arrhythmia mechanisms as well as procedural outcomes, and in addition to that, they also did what's called a 12-point arrhythmia score calculated for each patient at baseline and on follow-up. They identified 80 arrhythmias in 47 cases. There were 57 procedures that were formed, and access to the pulmonary venous atrium, meaning having to cross this baffle some way, either by a fenestration that was left open or by going trans baffle with a needle or an RF needle, that had to occur in 33 cases. There were 53 procedures, 16 of which were by a fenestration, 17 of which were by trans baffle puncture, and in two of those procedures, a retrograde approach was performed. The majority of arrhythmias identified were macro-reentrant, no surprise. Atrial flutter seems to be in everyone in the adult congenital world. There were 25 macro-reentrant circuits identified. There were eight focal atrial tachycardia or ectopic atrial tachycardia identified, 13 AVNRT, four accessory pathway, and four twin AV nodes. There were five patients who had VT, and then there was some undefined atrial arrhythmias in 21. The majority of macro-reentrant arrhythmias, 14 as you can see here, were cavo-tricuspid or mitral isthmus dependent. Once you get across the fontan, you're effectively doing the same maneuvers that you would do in a structurally normal heart. Although you have a little bit more work to get there, we are functionally doing the same things that you do when you do a flutter ablation, if it's CTI dependent. Moving on to cases involving single ventricle palliation. This is a 19-year-old with tricuspid atresia and congenitally corrected transposition. Functionally for you, all you can think of him as a single ventricle palliation to a fontan. Unfortunately, because of his congenitally corrected transposition, he had heart block, and he ultimately got upgraded to a biventricular pacing system because of severe ventricular dysfunction. He presented to clinic with signs of fulminant heart failure, and what ultimately amounted to many, many months of incessant tachycardia with a clear fracture in one set of his epicardial ventricular leads. Ultimately, he was being single site paced. When we dropped his ventricular pacing rate down, what you can see is this quite imperfect, I apologize, 15 lead ECG with ventricular pacing reduced to 50 beats a minute. This demonstrates beautifully re-entrant atrial tachycardia with negative waves in the inferior leads and positive flutter waves in V1 consistent with a right-sided perimitral atrial flutter. Functionally, the reason that he is perimitral instead of peritricuspid is that he has L-looped transposition with a functionally no right ventricle. His fontan pathway lives here, and his mitral valve is in the location of a normal tricuspid valve. He has counterclockwise atrial flutter around his mitral valve that would otherwise be in the position of the tricuspid valve were he to have a structurally normal heart. This is an injection, an angiogram, in the inferior extracardiac baffle in the right atrial, in the RAO projection. What you can see here, this is the fontan pathway. This is going up into the pulmonary arteries. And if you fix your eye here, what you'll see is there's a tiny fenestration here that's where there is dye moving from, or contrast moving from, the fontan pathway into the atrium, and then here is your valve. So ultimately, what you have here, AV valve, here's where your IVC would be if you didn't have this fontan baffle here. So here's your cabomitral isthmus. So here's the line of block that you're going to start creating. What you can see here are actual intracardiac electrograms from this case. Four surface ECG leads on the top with intracardiac electrograms from the mapping catheter in green and a decapolar reference catheter that was placed in the superior aspect of the baffle. The right atrium was accessed via the fenestration with a quadripolar mapping catheter and positioned right on the cabomitral isthmus. Entrainment mapping demonstrated concealed entrainment with a post pacing interval equal to the total tachycardia cycle length at 240 milliseconds and identical intracardiac activation pattern during pacing and during tachycardia. What you can see that's annotated as well is that when pacing from the distal bipole of the mapping catheter, the timing of the stem to P wave of 151 milliseconds and the intracardiac reference electrogram labeled ECB 1 and 2 of 93 milliseconds were almost identical to the electrogram recorded to the same site to the P wave 155 milliseconds. And 97 in tachycardia. The tachycardia couldn't be terminated. Sorry, the tachycardia terminated and could not be reinitiated despite aggressive pacing once that mapping catheter was placed on the cabomitral isthmus despite aggressive pacing maneuvers. So an empiric set of lesions was placed between the mitral annulus and the site of the IVC with bidirectional block confirmed at the end. And if you remember from that picture that we just showed, this is the line of block that we showed here. And lastly, one final case, which represents another nice example of a single ventricle atrial flutter case. So these are CARDO images from a patient with right atrial isomerism, which is basically a form of heterotaxy, congenitally corrected transposition of the great arteries and severe RV hypoplasia. So functionally for everyone here, think of them as single ventricle physiology with a fontan. The left panel shows the anatomic reconstructions of the intraatrial baffle and the pulmonary venous atrium seen from the left anterior oblique view created using CARDO. The left panel shows the anatomic reconstructions of the intraatrial baffle and the pulmonary venous atrium seen from the left anterior oblique view created using CARDO. The right panel demonstrates four surface ECG leads with intracardiac electrograms from the mapping catheter and the decapolar reference catheter within the baffle itself, the reference. A trans baffle puncture had to be performed in this patient because he didn't have that open fenestration. And what you can see here is once the pulmonary venous atrium was accessed, this is the same cavomitral isthmus line that we've done, that we did in the last case, just seen from a different projection. So the cavomitral isthmus line denoted in light pink spheres here to here, with entrainment mapping shown in this panel, showing a total post pacing interval equal to the total cycle, equal to the tachycardia cycle length and an identical intracardiac activation pattern during pacing was performed. So this linear set of RF applications was placed along the cavomitral isthmus with termination of the tachycardia achieved once the line was complete. So right here at the blue sphere. And often what you'll find when you're doing these cavomitral or cavotricuspid isthmus ablations in patients who have Fontan physiology is that you end up actually having to create a line within the pulmonary venous atrium here. But you also often have to reinforce that line on within the Fontan pathway and that's actually where it terminated here. This blue dot is actually being placed from the intracardiac baffle side once we came back across the fenestration. All right. So, despite the fact that most of the cases I've chosen to show you for today have been macro reentrant atrial arrhythmias, there were a number of other arrhythmia substrates that were identified in in these series. Including things like twin AV nodes, which you may have read about, but may have never actually seen. But functionally and just for fun. Twin AV nodes is this lovely EP phenomenon whereby you actually have two, an anterior and a posterior AV node that are connected by something called the Machenberg sling. And depending on how the activation occurs, you can actually have two distinctly different QRS morphologies. In addition, this sets up a way that you can have twin-twin AV node reentry. And there are cases where you'll end up doing an ablation of one of those AV nodes once you've determined which AV node you want to reentry. And there are cases where you'll end up doing an ablation of one of those AV nodes once you've determined which is the appropriate node to ablate for those patients. This is just a nice picture of two very different QRS morphologies in the EP lab. So this is your pacing that's coming down by your upper AV node with a slightly different QRS morphology, as you can see here. And this is antegrade via your lower AV node. And you can see this not just in the lab, but you can actually see it on surface ECG in these patients occasionally. So we started to bring these more complex anatomical substrates to the lab. We've talked about some of the studies that were early in the experience of complex congenital ablations and what they found. But one of the questions that always comes up is, what's the safety profile? What are the complications of these procedures? And at least in this large series that was published out of the Boston Group, there were really no major structural complications. There were the usual complications of hematoma. But there were no major structural complications. And there were, importantly, no desaturations following the procedure. People always worry that once you puncture through the Fontan baffle, you're basically creating a right-to-left shunt. And so will those patients be significantly desaturated? And unlike when you puncture across an atrial septum, which will heal up over time, this is usually made of Gore-Tex patch. So once you puncture through it, it's sometimes a little bit more difficult to puncture. But it's usually made of Gore-Tex patch. So once you puncture through it, oftentimes that tiny hole will remain there. But there's no functional desaturation that was seen in this series. So that's important for patients and families to understand. Finally, what patients always want to know is, will this actually make me feel better? As part of the BCH TCPC study, they did this arrhythmia survey for patients, both at baseline and post-ablation. And importantly, there was a significant decrease in the arrhythmia score over 18 months in follow-up. And this was a sustained trend that they saw. Even in cases where there was arrhythmia recurrence, patients' subjective experience was better post-ablation. And I think that's important for patients going forward. So what do we see when we evaluate the literature looking at the success of ablation in patients with congenital heart disease? No surprise that a lot of them have recurrence. This is just a listing of a lot of the big studies that have been done. And when I say big, I mean small in comparison to the adult studies that you guys look at all the time. We just don't have that volume of patients. But when you look at the major studies that have been published looking at congenital cardiac ablation, what you'll find is that there's a good acute success rate, but the risk of recurrence is quite, quite high. And whether this represents recurrence of the same substrate or a new substrate is difficult to say. But I think what most people who do this or have done this for an extended period of time would say is that the management of arrhythmias in the ACHD population is really a lifelong pursuit. I'm getting to the end of the time, so I'm going to leave you with these two final thoughts. In Quebec, every individual is assigned from birth a unique Medicare number in the first year of life that's used to track all their diagnoses and health services rendered and systematically recorded until death. In 2014, a group published some of this data from the repository aptly named the Quebec Congenital Heart Disease Database. They looked at patients from 1983 to 2000. And what you can see here is that the numbers and proportions of adults and children, and this is just in Quebec, so all comers, all congenital heart disease, and then severe congenital heart disease over time in 2000, 2005, and 2010 continues to increase substantially. From 2000 to 2010, there was an increase in the prevalence of all congenital heart disease and severe congenital heart disease in both children and adults. However, a much larger increase was noted in adults. And this data was from 10 years ago. So the reality is that these numbers just continue to get larger. So this now represents a growing need in our field and ultimately in your field as well. And finally, because we didn't spend a significant amount of time discussing atrial fibrillation, but it represents what I think is an area of limitation for pediatric electrophysiologists, at least certainly for myself, but an area of real expertise in the adult EP world. In 2015, Natasha De Groot and her group out of the Netherlands, in conjunction with John Cheidman out of the Boston Group and others, put together a series looking at the incidence of atrial fibrillation in aging patients with congenital heart disease. The aim of this multicenter study was to examine a large cohort of patients with a variety of congenital heart disease and to assess the age of onset and the initial treatment of atrial fibrillation coexisting with atrial tachycardia and the progression of paroxysmal AF to longstanding or persistent or permanent AF during long-term follow-up. They looked at just about 200 patients, 199 patients with 15 different types of congenital heart disease and documented atrial fibrillation episodes were reviewed. Atrial fibrillation develops on average at a mean age of 49 with a sort of range of about 17 years on either side of that. Regular sort of focal atrial tachycardia has coexisted with atrial fibrillation in 33% of patients. 65% initially presented with regular atrial tachycardia and then ultimately developed atrial fibrillation over time. In a subgroup of 114 patients, deterioration from paroxysms of AF to long-standing persistent or permanent AF was observed in 29 patients, which represents about a quarter of the patient population that was studied. And that happened on average about three years after the first atrial fibrillation episode was documented. In addition, TIAs and cerebrovascular accidents occurred in 26 patients, so also about a quarter. However, a substantial number of those occurred before the first known documented episode of atrial fibrillation. So whether this is silent in some of these patients is very, very likely. So just to wrap up, I think the management of heart rhythm disturbances in ACHD patients is an evolving and rapidly growing field. And this lecture basically touched on some of the atrial reentrant substrates and the anatomical substrates that you'll see in this population. But ACHD is a massive, massive field. Arrhythmia mechanisms encompass a wide range in the ACHD population, but despite the anatomical differences, some of which I've tried to simplify down for you all today, what you actually end up seeing is not dissimilar to the arrhythmias that you see in the general adult population and include, for the most part, classical reentrant circuits that you guys are seeing all the time in your cases. There are ablatable substrates in these populations and they correlate with improved symptoms, which I think is a really important thing to remember for these adult congenital patients. Despite significant advances in mapping and ablative technology over the past 20 years, recurrence and ongoing arrhythmia remains a problem for these patients. And then I think lastly, what I touched on finally is that atrial fibrillation will be a major issue for many patients, specifically those with single ventricle physiology in the coming years. And this is really an area where we don't have the interventional experience, but you all really do. So thank you so much for having me and for sitting through a lecture at five o'clock at night after a long day. That was great. Thank you so much. I guess if you had to give some advice to these adult EP fellows in terms of getting help from their pediatric colleagues, is there anything you would want to tell them? I think what I would say is just like we come to you for questions about resynchronization and atrial fibrillation, we are happy to help and answer and even come to be in the lab to help you understand the anatomy if you think that that's going to help you be able to understand the arrhythmia. The reality is, as I've tried to say throughout this lecture, is that once you get into the lab and start seeing the signals, what you're going to realize is that you're seeing the exact same things in the congenital population that you see in your structurally normal hearts. But it's really that understanding of the anatomy that can help you and we are more than happy, I think I speak for all of my, at least my colleagues on this side, we are more than happy to be those people for you if you feel like that will be helpful because it is complicated and sometimes it just takes more than one brain sort of looking at things and gaining some familiarity with that to understand exactly what it is that you're dealing with. But ultimately, the ablating is going to be much easier for you than you realize. And I mean, that's the way we've always approached it with your group is to involve you guys early and even simple things like tracking down the surgical reports to understand what happens. It's extremely important. There's clearly a question here from someone who's been frustrated. So in these procedures where there are numerous atrial arrhythmias, at what point do you resort to antiarrhythmics as opposed to ablating? Yeah, I think that's a great question. It's a really hard question. I don't have nearly the years of experience that many of my colleagues do. But I think what I would say is in my limited experience, what we try to do is ablate what we believe are the clinical or substantive tachycardia cycle sort of circuits. What we know is that when you get into these cases, specifically in the single ventricles and you find multiple circuits, it's less about elimination of arrhythmia substrate and more about mitigation of their arrhythmia burden. So if you can drop their arrhythmia burden from 80% or 100% to 40%, that's a win in many minds. And so I think oftentimes what we'll do or the approach that we'll take is we'll try to do an ablation. We'll try to map and get rid of the circuits that we can get rid of. And if there's a few others that are left remaining, then we'll treat them with antiarrhythmics. And then it's really a conversation with the patients about what their risk benefit ratio is about coming back to the lab versus maintaining themselves on antiarrhythmic therapy. As you know, some patients can't be on certain antiarrhythmic therapies for long periods of time because they just don't tolerate it from end-organ dysfunction reasons. But many of them can for some periods of time. So it's really sort of that balance of taking care of what you can and mitigating the burden of their arrhythmia as best as you can. Great. There's kind of a specific question here. How do you localize the HISS area in patients with a septum primum defect? Or maybe is there some anatomic localization of the HISS that would be helpful? Yeah. There's actually septum primum defects are usually not as big of a problem. You should be able to find the HISS in almost the same location. Sometimes when you have a true, true septum primum in association with a cleft, sort of like in a transitional AV canal, sometimes your HISS can be slightly lower. But what I would say is there's actually a beautiful series of pictures in the Moss and Adam textbook that looks at location of HISS in multiple... And I didn't talk about this specifically in this lecture, but it talks about the location of HISS in multiple congenital anomalies. What I would say is go to where you believe, especially in septum primum defects, go to where you think the HISS is going to be in a regular sort of standard EP study, and then walk your way down that septum into a more inferior location, and you may have success that way.

arrhythmias

adults

congenital heart disease

ACHD

atrial arrhythmias

atrial flutter

atrial fibrillation

ablation procedures

challenges

collaboration