So welcome everybody. This is core concepts in electrophysiology and the topic today is Tetralogy of Fallot. I'm Mitchell Cohen. I am the co-director of the Heart Center and chief of pediatric cardiology and director of adult congenital electrophysiology at Inova Fairfax Hospital. And this is going to be essentially a four-part series. This will be the first one. We're going to look at the physiology, natural history, and update on risk assessment for sudden cardiac death in Tetralogy. We're going to have three other speakers. One is going to touch on atrial arrhythmias in Tetralogy. One is going to touch on ventricular ablations and VTAC in Tetralogy. And the last speaker is going to talk on conduction system pacing and CRT in Tetralogy. So I get the honor of kicking off this session, so thank you all for joining. These are my disclosures, none of which are relevant to here. So Tetralogy of Fallot was first described by Neal Stinson in 1671 and Tetralogy is actually the most common form of cyanotic congenital heart disease. Neal Stinson was actually a Danish monk who was also a geologist, a paleontologist, and a pathologist. And there were others, a lot of other people who wrote about Tetralogy, but really Tetralogy as we know was really coined by this person, Étienne Arthur-Louis Fallot, whose name is eponymous with the condition. And essentially in 1888, he described four anatomic cardinal features seen in this defect, the ventricular septal defect, an overriding aorta, right ventricular outflow tract obstruction, and right ventricular hypertrophy. And it has a pathophysiology characterized by the VSD and the RV outflow tract that causes right to left shunting with low pulmonary blood flow and cyanosis in the early neonatal period. And the extent of the right ventricular outflow tract obstruction is highly variable. It may include hypoplasia and dysplasia of the pulmonary valve, as well as obstruction of the subvalvar and valvar region at the pulmonary outflow level. And the RV outflow tract obstruction is certainly progressive. And as a compensatory, there's right ventricular hypertrophy that really adds to the level of obstruction and really without specific surgical management, which was the case when Fallot was writing this, has up to a 35% mortality in the first year of life and 50% within the third year of life. And so really with this dismal natural history, interventions were really needed to change the outcome of not just this particular cyanotic congenital heart defect, but really all congenital heart defects. Now, in the 1940s at Boston Children's Hospital, Robert Gross was ligating patent ductus arteriosus. And at that same time period, Helen Taussig was at Harry Lane Hospital at Johns Hopkins. And she realized that these patients are really dying from cyanosis. And if there was a way to essentially keep the ductus open, that might help to alleviate the cyanotic symptoms that these patients were experiencing. So Dr. Taussig went to Dr. Gross, as the story is told, in the 40s, and asked him if he would consider a way to keep the duct open. Much to her chagrin, I think he declined and said he was in the process of closing ducts, not keeping them open. And with that, she went back to Hopkins and approached Alfred Blalock and Vivian Thomas, who was his lab assistant at the time. And Blalock was willing to undertake what later became known as the Blalock-Taussig and later even the Blalock-Taussig-Thomas shunt. The importance of this from an EP standpoint, now 100 years later, really relates to the fact that these patients who had a prior BT shunt had an increased volume load on their heart, increased cyanosis, and with that RV hypertrophy, so ultimately a later repair would need to be done, but it set the stage for some of their inherent risk factors for arrhythmias later in life. Now it was really this person in the 50s at Minnesota, University of Minnesota, Minnesota Children's Hospital, who really was willing to undertake repair of tetralogy and Seawalt Lillehei, who was really credited as being the father of congenital surgery, completed the first correction of tetralogy in August 1954. And between 1954 and 1960, Lillehei operated on more than 100 patients, six with cross-circulation and 100 using what was then known as a bubble oxygenator, with an amazing survival, if you think about it, in the 50s to 77% at 30 years. Now the movement away from repair in older children to a younger age really began by Barrett Boys in Australia, New Zealand, Kirkland in Alabama, and Aldo Castagnet at Boston Children's, where they really demonstrated that complete repair of tetralogy could be done safely in neonates and infants with relatively low mortality. And really there were improvements in bypass, reduction in the size of the ventriculotomy, transatrial trans-pulmonary repairs, and pulmonary valve replacements that all altered the course of congenital heart surgery as we know it. Now interestingly, in that early period, the preferred surgical techniques were aggressive right ventricular outflow tract enlargement using a transannular patch, pulmonary valvotomy, and a large right ventriculotomy, essentially for complete relief of RV outflow tract obstruction, despite resultant severe pulmonary regurgitation, because the pulmonary regurgitation at that time was really an afterthought. It was really thought to be a benign thing, nothing to really worry about. However, since the 1980s, late outcome studies have revealed that chronic pulmonary regurgitation can lead to RV volume overload and dysfunction, resulting in increased long-term morbidity and mortality. And currently most centers really employ surgical strategies that attempt to preserve the pulmonary valve annulus and the valve in order to limit the degree of pulmonary regurgitation. So where is all this really kind of going from a historical standpoint? Well, this was two patients who were essentially, underwent tetralogy of fallot repair at around the same time period, almost the same age and almost the same follow-up. And you can see on the left side of the screen, an enormous size heart and on the right side, a fairly normal sized cardiothymic silhouette. So what was really going on? Why, why was this happening? And it became clear to the people that were studying it, that this was a very serious problem. And it became clear to the people that were studying adult congenital heart disease at the time, and this was Mike Itzolos, Andrew Reddington and James Somerville at the UK. And what they found was that those patients who had a restrictive physiology predicted better health outcomes, a smaller heart and chest X-ray, a smaller right ventricle and better exercise tolerance. But they also noticed that the group of patients that had a non-restrictive right ventricle, that big dilated right heart, had a much wider QRS right bundle branch pattern. Two weeks after sort of kind of almost getting done this manuscript, a TET patient was admitted to the Brompton in heart failure and monomorphic VT with sort of a typical left bundle inferior access. And it just so happened that this patient had one of the longest QRS durations in sinus rhythm with the right bundle branch block. And it was with that, that they were able to essentially publish this landmark paper that showed the mechanical electrical interaction in tetralogy, sort of a very seminal paper in the 1990s. And they realized that QRS prolongation predicted VT and sudden cardiac death. And while we may think of this as pretty sort of standard almost in the 2024 era, where we know that why QRS predicts heart failure and poor outcomes, this wasn't really all that known in the congenital heart population at that time. And so when you looked at those patients that had a restrictive physiology following tetralogy, you can see that they have a much shorter QRS duration compared to those that had a non-restrictive QRS duration. And if you use this sort of categorical variable of 180 millisecond QRS duration, it was very clear at that time that those patients that had syncope and sudden cardiac death had a much wider QRS duration with the right bundle branch block. In fact, all of the patients who had syncope and sudden cardiac death had a QRS duration above 180 milliseconds. And for the next 20 years, we're going to try and figure out what are the real risk factors? Who should have a pulmonary valve? At what point should they have a pulmonary valve? Who's really at risk for VT? Who should have an ICD? So this takes us up to about 1995 to 1998. And essentially this talk then sets the tone for the next 25 years. The actual area incidence of clinical sustained VT and sudden cardiac death is estimated to be about 12 and 8 percent respectively, 35 years after corrective surgery. But it was really this paper that was the start of risk stratification. Sudden cardiac death is the most common mode of death in tetralogy, occurring at about 2 percent per decade. The annual incidence is 0.15 percent. Risk stratification for life-threatening VT and sudden cardiac death is elusive. It was elusive 20 years ago. It remains elusive. And this talk is going to highlight that sort of nature to it. Why? Well, there's a lack of large prospective studies to really support some major evidence-based decisions. As an example, pulmonary regurgitation is recognized as the substrate for VT and sudden cardiac death. However, proceeding with pulmonary valve regurgitation does not completely remove the risk for VT and sudden cardiac death as myocardial fibrosis is still present. So the bottom line is there is not one risk factor. So how should we risk stratify the tet patient? Well, thoughtfully and carefully. That seems to be so logical, but not so simplistic. I want to just point out this slide and there's going to be another whole talk on it, that atrial reentrant tachycardias are a very common late occurrence after tet, maybe upwards of a third of patients, and it can be associated with sudden cardiac death. We're going to focus a little more on ventricular arrhythmias, but I don't want to lose sight of the fact that these patients have a high proclivity for atrial reentrant tachycardia, and especially those that have greater biatrial dilatation. So let's look at initial. When we talk about initial risk stratification, what was really happening was that people were looking at their tetralogy of patients with ICDs and comparing those that had VT and got shocked to those that did not have VT and did not get shocked. Now, we should always remember that ICD shocks are not a surrogate for sudden cardiac death, and we sometimes tend to jump into that a little too much. This was one of the first papers that looked at early risk stratification. This is a paper from Dr. Carey in a multicenter study that looked at 121 tet patients from 11 institutions, median age was 33 years, appropriate ICD discharge. Now, these are obviously high-risk patients because they already have a defibrillator, occurred in 31%, and of those that had appropriate ICD discharge, 37% actually had a positive EP study, and we're going to come back to that later on. So in patients with an ICD, a positive EP study predicted who would receive an appropriate shock. Again, not the same thing as sudden cardiac death. But they were able to look at those patients and come up with a couple of risk factors and say, well, if you have these risk factors, you're more likely to get an appropriate shock. So elevated LVN diastolic pressure, non-sustained VTAC, ventriculotomy, a wide curious which we talked about, and inducible sustained VT. Again, predicting annual rate of appropriate ICD shocks. And they were able to sort of attribute different points and risk score and predict who might have appropriate ICD shocks and place patients into low and intermediate and high-risk categories. Now, when we look at Tetralogy, there are a number of sequelae that begin day of life number one. There's increased right ventricular pressure. There's degenerative remodeling and fibrosis. There's dyssynchrony. There's cyanosis. There's volume overload. There's RV afloat tract aneurysms potentially. There's patches where the VSD was closed. There may be conduit material. There's dyskinesis. There's slow conduction zones. There's LV dysfunction. All of those things come together. There's not one single pathophysiology process, but really this whole composite process with chronic pulmonary regurgitation, chronic RV volume overload for pulmonary regurgitation, underlying right ventricular bundle branch block, fibrosis, hypertrophy, dysfunction. And all of that comes together to result in adverse electrophysiological remodeling, which can lead to VT and lead to sudden cardiac death. For simplistic purposes, I think I sometimes look at Tetralogy patients into two buckets, if you will. One are the group that have a really burned out, dilated right ventricle, years of pulmonary regurgitation. The right ventricle is barely squeezing. The left ventricle is barely squeezing. Those patients are at risk for sudden cardiac death and should have ICDs. Those are the easy ones. What we're going to spend this large talk is really those patients that are at risk for monomorphic ventricular tachycardia and sudden cardiac death. Monomorphic VTs account for more than 80%, and they rely on macro reentrant circuits occurring in the RV. So the substrate of macro reentrant VT tends to be scar mediated. It's different, as I mentioned, than the burned out, severely dilated RV that will only go straight to VFib. And Dr. Jeremy Moore is going to give a subsequent talk within this core concept. He's going to spend a lot of time talking about these isthmuses that are critical to starting and sustaining monomorphic VT. Isthmus 3, which is between the VSD patch and the pulmonary valve annulus, is the one that is the most common. What we're going to focus on for the rest of this is risk factors. What are the risk factors for VT, VF, unexplained syncope, and sudden cardiac death? And I essentially put these into three buckets, those with demographic risk factors, non-invasive invasive risk factors, and invasive risk factors. Again, before surgical correction of tetralogy, the RV, the right ventricle, is subjected to pressure overload and cyanosis due to RV afloat tract obstruction and right to left shunting through the VSD. Pressure overload and cyanosis are even more pronounced when palliative procedures, such as the modified VT shunt, are done to really delay a full repair and continue to promote pulmonary arterial growth. Now, a meta-analysis was published in the literature looking at tet patients from the decade 2008 to 2018, and endpoints were VT, cardiac mortality, VT, all-cause mortality. To enter into this meta-analysis, you had to have at least 100 patients and more than 10 events. And the risk factors for cardiac death or VT, when you looked at the odds ratio, prior shunt, transannular patch, ventriculotomy, and the number of thoracotomies. So the complexity, palliative procedures, big scars, all increased your odds ratio of VT and sudden cardiac death. Now, I will be the first to say that surgery today is not the same as surgery in the 1950s. There is a decreased need for ventriculotomy. Surgery is being done at a younger age. There's better perfusion. There's better ICU care. And parallel to the incredible progress that surgeons have made over the years, there's also been tremendous post-operative care that have also shaped clinical outcomes for years to come. And so when we look at series from the 60s and the 70s and the 80s, we shouldn't really expect the same thing from surgery done in 2020, but there are some commonalities that we'll talk about. So we know that older age of repair, older age of follow-up, older age of pulmonary valve replacement, surgical era, all increased your risk of VT and sudden cardiac death and increased your rate of appropriate ICD shocks. Also, heart failure and unexplained syncope are also demographic risk factors to pay attention to, as well as palpitations that seem suggestive of a reentrant arrhythmia, be it atrial or ventricular. When we talked about this, we shared that QRS duration above 180 milliseconds is strongly associated with VT and sudden cardiac death, but hold that thought for one second. The initial QRS 180 paper was from an early surgical era, and contemporary surgery may be associated with a narrower QRS, but a persistent arrhythmic risk. So most patients we see today with Tetralogy have a QRS duration less than 180, but we should not in isolation think of that patient as de facto no risk. In fact, if you look, this is a patient of mine who's a 20-year-old Uro-Tet, whose culture had a 12-beat run of non-sustained VT, and there's barely even any sort of abnormality in the right ventricular conduction system. In fact, there's a little bit of left axis deviation. So are they really at zero risk? It's important to realize we look at QRS duration over time. It's not a static number. And in fact, the patient with the QRS duration that's staying between 171 and 181, shown in the yellow, may be less concerning to me than a patient whose QRS jumped from 135 to 178 milliseconds. So QRS should be a continuous variable. It is not a dichotomous variable. Well, appearances matter. And this is something that's come up over the last few years, understanding what's called QRS fragmentation, which really is a surrogate for myocardial fibrosis. So in this study, QRS duration above 180 milliseconds only predicted 28% of the patients with mortality. But if you had moderate QRS fragmentation, at least four leads, it predicted mortality 41% of the time, and 46% if there was more than five leads. This is a patient that I saw last week in clinic. This is a patient with QRS fragmentation. This is a typical right bundle branch block post tetralogy of Fallot. And this is what fragmentation looks like. There it is in V5. There's clearly fragmentation in lead V2. Now, one of the really incredible studies that came out in the last year was something from the DIT4F Nationwide French Registry that is a registry that looks at long-term follow-up of a large, large cohort of patients with tetralogy followed longitudinally, but they also happen to have an ICD. So of the 144 patients in this study, the mean age was 42, at least one VF episode occurred in about 40% of the patients. QRS duration above 180 milliseconds and QRS fragmentation had hazard ratios of two and three and were significantly and independently associated with VT. And so if you look at this, the incidence of VT, VF overall, you can sort of see that QRS fragmentation and duration are of concern. In fact, QRS fragmentation was the only risk factor independently associated with appropriate ICD therapy in patients with primary prevention ICDs. Non-sustained VT, which we had talked about earlier, actually was not even shown to be a risk factor in this study. So severe RV enlargement, RV dysfunction, LV dysfunction, like acquired heart disease, ventricular dysfunction is a risk factor for both heart failure, VT, and potentially sudden cardiac death. Post-repair pulmonary regurgitation is commonly found in tetralogy patients. And it's the main culprit for VT and it's the main culprit for adverse RV remodeling. And certainly PR is usually tolerated due to RV hypertrophy. There's low capacitance of the pulmonary circulation. There's high heart rates, which limits the duration of dialysis and hence the pulmonary regurgitation volume. But over years, chronic pulmonary regurgitation fuels a vicious cycle in which volume overload initially increases leading to increasing RV dilation and decompensated phase with decreased RV mass volume ratio, higher well stress, RV dysfunction, and you get reverse remodeling with changes in histology, RV architecture, impairment in the atrium, RV-LV negative interactions, and electromechanical dyssynchrony. So pulmonary regurgitation is the hemodynamic substrate responsible for ventricular and sudden cardiac death. Does correcting pulmonary regurgitation solve everything? Well, this was a recent paper that came out that is an incredible paper that's certainly worth reading. It was a prospective study examining the prognostic value of delayed gadolin enhancement on MRI and to construct a weighted risk score for death and VT, incorporating all independent risk factors to help identify high-risk patients who should be considered for an ICD or preventative VT ablation or more heart failure advanced therapies. So as a prospective study, all patients had to be older than 16. They had 550 patients with Tetralogy who underwent cardiac MRI. And they found that the greater the degree of delayed gadolin enhancement, the more myocardial fibrosis, the worse your survival was as shown on the left, and the worse your predicted freedom from ventricular arrhythmias shown on the right. And with that, they came up with a composite score looking at MRI data, exercise VO2 data, and BNP blood levels. And what they found was that the group with the highest risk score had a 4.4% sudden cardiac death risk and should be considered for an ICD. And there was 3.7% that had VT and should also be considered for an ICD or VT ablation. So on the left is predicted survival and time since the initial scan. And for the first time, we really show that late gadolinium enhancement in these patients in a large scale study is prognostic, justifying inclusion into clinical practice. And there's a very reasonable weighted risk score here that looks at who should potentially get an ICD. Interestingly, non-sustained VT also in this study was neither associated with mortality nor significant ventricular arrhythmias. Now, we know that pulmonary regurgitation leads to an increase in right ventricular end-diastolic volume. We know that if you have an increase in right ventricular end-diastolic volume, your right ventricular ejection fraction drops off. And if your right ventricular end-diastolic volume increases secondary to ventricular-ventricular interactions, your left ventricular ejection fraction also decreases. So this was a paper that looked at risk of cardiac arrhythmias following MRI. So they have 319 patients who underwent cardiac MRI imaging at two centers. And looking at that, they showed that your increase in RV end-diastolic volume, your increase in your RV end-systolic volume, the decrease in your RV ejection fraction, and an increase in your QRS. Incremental changes continue to show incremental risk for ventricular tachycardia. Now, if we look at the indicator study from probably almost a decade ago, this was a study that looked at 873 repaired TET patients. They looked at clinical outcomes, ECG, exercise, MRI. 4% approximately reached the primary outcome of death or sustained VT at a median age outcome of 38 years. And they came up with three things, RV mass volume greater than 0.3, LV ejection fraction less than negative two, and atrial arrhythmias. So we're starting to see that decrease in LV function and atrial arrhythmias should also be considered in the risk factors. RV hypertrophy, ventricular dysfunction, atrial arrhythmias were predictive of death and sustained VT. It's important to realize that we've been following TET patients for a long time. And this was a wonderful study. This is a forest tree plot, but basically you can see that really regardless of era, the presence of LV dysfunction is a concerning risk factor no matter when you were repaired. This is some new data that also showed that we've been spending so much time looking at right ventricular and diastolic volumes, but leaving patients with right ventricular outflow tract obstruction may also increase your risk for VT and sudden cardiac death. So when I put it all together, the non-invasive risk factors, there's a whole host of them. There is not one single risk factor. They're all weighted. Some you may pay more attention to, and there's likely more to be added. There is not a single standalone non-invasive risk factor. There is no single non-invasive Holy Grail risk factor that's going to predict who's going to get VT and sudden cardiac death. Well, we've talked about demographics. We've talked about non-invasive. Let's shift a little bit to invasive risk factors. There's been a constant effort since the 1980s to define the role of invasive EP studies in predicting clinical VT and sudden cardiac death. This is a multi-cohort study from Dr. Carey and colleagues that looked at 252 patients with tetralogy who underwent program V-STIM at about 18 years of age, and they followed them. Clinical VT and or sudden cardiac death occurred in about 25%. It's important to realize also, as I mentioned earlier, that 60% of the patients had clinical reasons for coming to the EP lab, whether that was unexplained syncope or non-sustained VT. So this was inducible predictors. And what they found was that age of the study, palpitations, all increased your risk factors. So if you look at this, the sensitivity of whether a V-STIM study predicts future monomorphic or VT was 77%. So a positive predictive value of 55% and a negative predictive value of 92%. So if you are coming for a V-STIM study and it's negative, singles, doubles, triples, baseline, isopryl, two sites, that is fairly reassuring, at least in this study, that you're not going to have future VT and or sudden cardiac death at least in the next five to 10 years. Now, invasive EP testing really should be sort of looked at in a Bayesian kind of way. So if you accept a 3.5% annual risk of sudden cardiac death as a reasonable cutoff value based on ICD primary prevention trials, program V-STIM would be helpful in further risk stratifying patients with a pre-test probability somewhere between one and 11%. So in other words, if your pre-test probability is below 1% of sudden cardiac death, an EP study is probably not going to add much. It's not going to change who should get an ICD. Similarly, if your pre-test probability is greater than 11.5% for sudden cardiac death, V-STIM probably is not going to change your clinical management. Those patients are probably getting an ICD anyway. So if we go back to sort of looking at a systemic, systematic EP study prior to PVR, this was a multicenter study prospective conducted to systematically assess EP study with program V-STIM in patients with tetralogy between 2020 and 2021. They had 120 patients enrolled. Sustained VT was induced in 22%. As I mentioned, I talked about isthmus three between the VSD patch and the pulmonary annulus. And what they showed was that factors associated with a positive V-STIM study, atrial arrhythmias and a wide pulmonary annulus, because maybe that area underneath the RV outflow tract, maybe it's not the entire RV outflow tract, but that area underneath the right ventricular outflow tract like where isthmus three is, means you're more likely to have ventricular tachycardia. The interesting thing about this is that the positive study led to a change in the management. Either patients underwent a catheter ablation, a surgical ablation, or had an ICD placed. More importantly, EP study at least six months later was negative in 90%, and no patient experienced sustained VT, and albeit this is a short follow-up study. So what is the timing for PVR? Does it change who should have VT, sudden cardiac death risk stratification? Well, this is a very early study that sort of tried to answer that question of whether pulmonary valve replacement changes your risk of survival in VT. It was a matched control, QRS matched control study. And they really found that the probability of freedom from VT did not matter timing of preventing VT based on the presence of getting a pulmonary valve. In a more recent study of TET patients with an ICD enrolled from 40 centers with a median follow-up of seven years, 26 patients underwent pulmonary valve replacement. Now, on the left-hand side of the screen are appropriate ICD therapies in red dots. The blue hearts are where they get their pulmonary valve replacement, and the right is what they look like afterwards. And you can sort of see there's a lot more red dots on the left side of the screen, a lot more appropriate ICD therapies. And it would seem that pulmonary valve replacement really does decrease your risk of appropriate ICD therapies for VT afterwards. However, all of these black hash marks were where patients had VT ablations. The risk cohort of high-risk TET patients implanted with an ICD, the burden of appropriate ICD therapies was significantly reduced. However, we shouldn't lose track of the fact that a number of these had VT ablations as sort of does that alter the overall clinical outcome? And those patients certainly are gonna need to be followed prospectively to see what is the impact of VT alone before pulmonary valve, after pulmonary valve replacement, sorry, what is the impact of VT ablation before and after pulmonary valve replacement? So what is the ideal time? Where is the inflection point to replace the pulmonary valve? You certainly don't wanna replace it too soon or patients are gonna have prior multiple valves, but you also sometimes don't wanna replace it too late. So this was a study that looked at primary outcomes, VT, sudden cardiac death in patients undergoing pulmonary valve replacement from proactive criteria on panel A and conservative criteria. So if your right ventricular end diastolic volume was greater than 160, but less than 180, this was sort of proactive. If it was greater than 180, it was conservative and likewise. And you can see that whether you met proactive criteria or conservative criteria placing a pulmonary valve as shown in red, sorry, shown in blue, decreases your incidence of VT and sudden cardiac death. As opposed to the red, you can see those patients did not get a pulmonary valve replacement and they continue to have a higher than normal risk of VT or sudden cardiac death. However, whether you looked at the proactive or the conservative, if you did not meet criteria, you just put a valve in, it does not alter your risk of VT or sudden cardiac death. So proactive, again, you had to have at least two or more of the following criteria depending on which category you were in. And that's shown a little better here that if you did not meet proactive criteria, in other words, your right ventricular end diastolic volume let's say was under 160, you had normal RV function. Your cure restoration was above 160 and that was the only criteria you fell into this bucket where it does not alter your outcome. So the pulmonary valve replacement reduces your risk of VT or sudden cardiac death if you meet criteria. But I also want to point out one thing, even though the reduction in VT and sudden cardiac death is less, it's not zero. So by no stretch of the imagination, just because you put a pulmonary valve in somebody after tetralogy, it does not decrease your risk of VT or sudden cardiac death, largely because there's probably fibrosis there. There's probably a bunch of other adverse remodeling that sets that individual up for VT or sudden cardiac death. So sometimes we get to data versus gut. There's a lot of guidelines out there that talk about this. This was the prevention study that looked at other risk factors that we don't think about necessarily in congenital heart disease, but in adults, coronary artery disease, QT dispersion, ventricular dysfunction. You can see the more risk factors you have, the greater your risk of sudden cardiac death. So to end with, how do you create an integrated risk stratification model? Well, we certainly talked about demographic risk factors, older age of repair, older age of pulmonary valve, prior VT shunt, ventriculotomy, number of cardiac surgeries, and then a bunch of noninvasive risk factors listed here. So if you are a low risk patient where your risk of sudden death is probably less than 1% per year, you can probably just be followed conservatively. Similarly, if you add up all of your demographic and your noninvasive risk factors, and you have a high risk of sudden cardiac death, those patients should probably get an ICD. The intermediate group whose risk of sudden cardiac death whether it's some noninvasive, some demographic puts that individual here, that may be the situation where EP testing will point you one way or the other way. If you have easily inducible VT and you're in this intermediate risk, does it push you here and you should get an ICD? Or if it's negative, does it push you here and you don't have to have an ICD? And lastly, how will VT ablation and pulmonary valve replacement impact this risk stratification model and who should get an ICD? At the end of the day, I think it's important to look through the lens of multiple team members. EP, cath, imaging, adult congenital, APPs, surgical lens, we all come at this from a different vantage. And I think it's important that when we risk stratify patients, we're not just wearing our single one view lens, but we're looking at it from all different vantages. And with that, I thank you very much. ♪♪

Electrophysiology

Tetralogy of Fallot

Cyanotic congenital heart disease

Sudden cardiac death

Pulmonary regurgitation

Ventricular tachycardia

Pulmonary valve replacement

Risk stratification model