Hello everyone, I'm Chris McLeod, I'm one of the cardiac electrophysiologists at Mayo Clinic. I specialize in treating patients with congenital heart disease who have arrhythmias and for this heart rhythm board review course, we are intending it to be a broad overview for all of you taking the exam, but also just some really helpful key differences that are going to be useful in your practice and we know that these are patients that you don't see every day, but they are definitely patients that are going to be coming through with arrhythmia issues, whether it be bradycardia or tachyarrhythmias. And so yeah, it's a broad overview, starting off with the most common, which is atrial arrhythmia. We'll go through those common disease patterns and how they present, just those differences are important and how we recognize where things have gone differently because of the patient's congenital heart disease background and what we do differently from a practice point of view and we'll look at those current best practices as EPs. This doesn't affect this talk. Just a little bit of background, I found this interesting, it was Paul Friedman showed this in a slide and it really caught my attention. Congenital heart disease and arrhythmia has been wedded since the early 50s and before the heart-lung bypass machine, the mother you can see there on the right was serving as the circulation for the infant that was being operated on and it was soon after this that the cardiopulmonary bypass advent began and really transformed management of babies and children with congenital heart disease and really impacted survival. But it was very early on in that setting that it was recognized that these patients really struggled from bradycardia after surgery, a lot of AV block and you can see there one of the early pacemakers that are being wheeled around and connected to the wall. And so this was the precipitator in Minnesota for the beginning of Medtronic, it was Earl Bakken who was the mechanic in the hospital at the time, who was tasked by Lily High, the cardiac surgeon to come up with something that was going to be more reliable than that big box on wheels and that really was the precipitator for starting his own company with his cousin in their garage in Minneapolis. So right from the early ages of congenital heart disease surgery, arrhythmia has been managed from that early start. You can see here on this timeline, cardiopulmonary bypass is brought in towards the end of the 1950s. You can see that even then up until the 80s, most patients would succumb before the age of 15, most actually within the first year of life. And then you can see as we get better at managing not just arrhythmia but also managing all of the cardiac surgical techniques and the management of care thereafter that these patients are now surviving into adulthood and most are living into their late teens and beyond. You can see here the change in mortality over time from the 1970s down to now. It is different for each syndrome, you have the univentricular heart there with higher risk versus tetralogy, the poster child of really complex congenital heart disease where patients do really quite well. So different syndromes lead to different outcomes and also different arrhythmias which we will review. You can see here the risk of death really just shown in a different presentation style with ASD being one of the more simple diseases and patients surviving much longer. So that improvement in cardiac surgical techniques and arrhythmia management led to these patients surviving. There now are millions of them in the United States. The adults are outnumbering the kids with congenital heart disease and the population is still continuing to grow at about 5% per year. What are the implications? There really is this burgeoning increase in the need for care for these patients since the early 2000s and just keeping up with delivery of health services including arrhythmia management. More specifically, let's break it up into these four groups. The bradycardia and devices, atrial arrhythmias, sudden cardiac death or ventricular arrhythmias and then we will focus in on just anticoagulation. So atrial arrhythmias are the most common reasons why these patients will come into hospital. It's because these patients are living longer, they've got scars in the heart and as EPs we know this leads to reentry. It's also the most common cause of morbidity. This is an age timeline for these patients along with the incidence of atrial arrhythmias in all comers with congenital heart disease. This is from the Canadian group in Toronto looking at their population. By the age of 50, you can see here almost 50% have had an atrial arrhythmia of some kind, asymptomatic atrial arrhythmia. So much higher than the normal population. You can see for atrial arrhythmias, just the more scars that you have in the heart, the more likely you are going to have atrial arrhythmias with the atrial switches, the Mustans, Mustards and Sennings being the most common. If any of the patients do develop an atrial arrhythmia, as mentioned, it really is affecting morbidity but also mortality, stroke and heart failure. When we think of mechanism, it's nice to go back to this conceptual framework from Kumail where you have substrate, you have triggers and you have the modulators. For congenital heart disease, this is almost all going to be substrate. We've got diseased myocardium that is being repaired. There's a defect which is going to provide a boundary for reentry and also for reentry to occur. It's just so much easier where you've got large atrial size that allows for that activation wavefront to proceed and not be extinguished. Hypoxia is also thought to affect arrhythmogenicity and also conduction velocities. Here is a postmortem specimen from a patient with an ASD. You can see just with one of our most simple congenital heart disease syndromes, just how a simple lesion left uncorrected over years will lead to massive changes in the volume of the atrium. You can see the left ventricle here, very similar size-wise but this enormous change or the right-sided chambers allowing for easier perpetuation of reentry. A caricature then for a take-home slide as to what we conceptually understand when we are speaking about reentry where there are boundaries from either an anatomic defect or a patch or a scar and tethered around that is tissue which has been sutured and not conducting as quickly. That also changed the refractory periods and leading for differential reentry in some patients. The most common type of atrial reentry then is going to be what we call IART, intraatrial reentrant tachycardia. It is a flutter and that's how it's referred to in the congenital literature. It's a flutter that doesn't exclude the cabotrichospodismus but very often does include the boundary zones that are provided by scars and defects. Switching then to one of the other components of atrial arrhythmia or if you were seeing a patient in the ER in an atrial flutter with heart rates in the 130 beat per minute range and you thought, well, this patient may need to be cardioverted as a first step in stabilizing these patients. There is some anatomy that's useful for electrophysiologists to take home in that setting. What you can see here is that the heart is being bypassed essentially by the return circulation, so IVC, SVC being redirected straight into the lungs. This is the original Fontan. It's done slightly differently now as a bicaval anastomosis. But this chamber of Fontan tissue, which is historically remodeled atrial tissue, just dilates and dilates and becomes a nidus for clot. And so there are case reports and there are concerns that these chambers over time as they dilate, and here is a view from a TEE, that very large thrombi can form in them. They can be calcified, they can be laminated, but they can actually be quite mobile too. And even if these patients have been on an anticoagulant, there can be large thrombi in them and I would, as a first step in managing atrial arrhythmias in this group, move ahead with TEE before cardioversion as you can dislodge some of these thrombi and they can be fatal moving from that Fontan directly into the lungs as a large saddle pulmonary embolus. We know if we just cardiovert these patients alone, that recurrence is almost certain. It's going to happen in the majority of patients and so something needs to be done in addition to cardioversion. We haven't changed the underlying substrates. Another important point to recognize seeing these patients either in the ER or just clinically is that they don't always present with a faster than normal sinus rate. In some of these cases, it may be easier to see the flutter waves as you can hear in this bottom lead, but sometimes it really isn't that clear. The P waves can be hidden in the QRS and in the T wave and you may think that this is just a faster sinus rate because they just don't have the compensatory mechanisms because of the congenital heart disease. So if you are curious as to whether this is sinus or whether this is an atrial arrhythmia using Valsalva in the office or while getting the 12-lead ECG or even Adenosine in some of those patients blocking the avenote and seeing is there something underneath there that is a 2-to-1 flutter and not a 1-to-1 tachycardia. Typically though with any patient presenting with faster heart rates, we would obviously examine the hemodynamics and make sure that we're not missing anything hemodynamically first that may be triggering some of the atrial arrhythmia or driving a sinus tachycardia. Here's another example of a different patient with an atrial tachycardia, one of these intra-atrial re-entrant tachycardias, a scar-related flutter that is 2-to-1 and then as that patient starts to get up and exercise very quickly, a different step up in the ventricular response. So we pick this up quite commonly on exercise tests. The patient goes for a treadmill, the resting heart rate is 100 and it's not a gradual increase but a very abrupt step up from what is 2-to-1 flutter or 2-to-1 scar-related tachycardia to a 1-to-1 and here you can see some variable block. So this is an example of a different patient, very difficult to see P waves here but as soon as they started to exercise, went straight from a 2-to-1 to a 1-to-1. So be careful of that or be aware of that when looking at the exercise testing. So it is less common actually for us to see atrial fibrillation. We obviously do see it. It's in the sicker congenital heart disease patient. It's in the older patient who is 60s and above typically who has developed some of the comorbidities. They have some diabetes, they're overweight, they have some diastolic dysfunction and their left atrium has started to enlarge. But more commonly, it's going to be this interatrial reentrant tachycardia, the scar-related flutters that you see and because of the diseased tissue, because of the bigger atria, that atrial rate of the flutter is slower. So instead of it being what we usually think of for typical CTI flutter, Kevatricuspidismus flutter in a normal heart with a cycle length of 240-260 ms, it may be 300-310 and it may conduct very quickly and those P waves may be hidden. Because it's a slower cycle length, it's very difficult to rate control these patients. If you think of a cycle length of 340 ms, it's allowing time for the AV node to recover and so trying to beat a block or use a calcium channel blocker for these patients, very difficult to get effective rate control. We're almost always moving to rhythm control for these patients. Rhythm control, really have to avoid your class Ic drugs, propafenone and flecainide will slow that even further, will lock them in flutter and it will allow for one-to-one conduction or be more likely to allow for one-to-one conduction down the AV node because you've slowed the cycle length of these. So Sotilol, Tecosin, Amiodarone are your drugs of choice, all well-studied in congenital heart disease. An older electroanatomic map showing scar and a small isthmus conducting up between the scar and the valve, here's one of our cases using high-density mapping. You can see on the left the substrate with red and gray being scar, here I was pacing over these areas, could not capture, labeling them as scars and then really very little ablation necessary. Here's the activation map and you can see conduction through the small isthmus and anchoring from scar to scar and then after that obviously checking for bidirectional block, those would be the two key things to do. After this, our team would move ahead with burst pacing on and off isoproteranol to try and induce other flutters and really taking care of any of those diseased areas where you've got very broad, diffuse, fragmented, fractured electrograms that are accounting for slow conduction that may in fact lead to flutters in the next few years after ablation. Another example here of a patient with a right atrial flutter, we're looking at the back of the heart here is an atriotomy scar also up here, but a small gap in this perpetuating through and around and ablation through here also ended up anchoring to the SVC and proving bidirectional block. Here's the substrate map you can see. Making sure that the diseased areas really are ablated. I'm typically pacing over these areas at 10 milliamps, 2 milliseconds to make sure that there is block, non-capture before checking for bidirectional block with our catheters. How good are we at ablating these arrhythmias? There's been lots published since this older study but still mirrors the same kind of approach and I'm interested to see whether PFA will change this. We do a very good job at treating the initial clinical flutter, 80% or higher, but because of all the other scars we see different atrial arrhythmias occur over the next five years. So I would frame that for the patients in that way if they come in in the flutter or we can easily induce the flutter we're almost always going to be able to map and ablate that successfully but there are other areas and that's why really preemptively looking for other areas with high high-dose iso and pacing and then taking care of flutters which really aren't clinical now but can cause trouble in the future. All right we're going to change gears and switch to pacing from atrial arrhythmias. Just know the anatomy. As an electrophysiologist get a CT, get a venogram. I have been seeing patients before where pacing docs have tried to put down leads not realizing that you just can't reach the heart because there was a Glenn procedure. So just doing a CT. The CT is also really very useful not just for the obvious mechanical valve which you don't want to cross but for intracardiac shunting. That's probably the most common issue or risk that I see with placing a lead. If there is a shunt at an atrial or a ventricular level then any thrombus that develops on your pacing lead has the opportunity to cross to the systemic circulation and lead to stroke or some other systemic embolism and so making sure that there's no shunting before putting leads down. If there is then think about closing that before putting a lead down or you're going to be thinking about epicardial or maybe and there are some early studies maybe some of the leadless pacing devices. So really key there know your anatomy and use as much imaging as you can. Another reason for knowing the anatomy is just remembering and this is a patient with a mustard procedure so an atrial switch. There was a procedure performed when the patient was an infant and we are redirecting blood. So this is an atrial switch redirecting blood from the SVC into the sub pulmonic ventricle and then also from the IVC into the sub pulmonic ventricle. So switching the atrial return in a patient with detransposition. Those details may not be necessary but definitely imaging and you can see this with contrast and a CT or just you may sometimes if there's very slow flow need a venogram. You can see injection into the SVC blood drains back and you can see a beak is being formed here. You can see where there was shunting of blood from SVC into the systemic atria that this needs to be closed so that any so that blood doesn't shunt and if you're going to put down a lead so that clot doesn't shunt across into the systemic circulation but you wouldn't be able to put a lead down here and occlude your SVC without risking consequences of SVC syndrome and baffle occlusion. So imaging and then ultimately referring to a center where that can be dilated, stented and then after the narrowing has been addressed then going ahead and placing a lead through there. So the take-home point is relying on imaging, recognizing that a lot of these procedures were done when these patients were children and things have changed over the years. Let's move then to ventricular arrhythmias. Sudden cardiac death is a real issue for these patients and it's related to ventricular scar. The same kind of mechanism that you saw in the atrial arrhythmia discussion and then there is also a group of patients where because of the different hemodynamic loads that there is failure of the right ventricle, usually a systemic right ventricle or failure of the right ventricle because of pulmonary hypertension. But this is a major cause of mortality. It's either this or progressive heart failure that these patients are going to succumb to as they get older. So let's draw a distinction between these two mechanisms of ventricular arrhythmias in patients with congenital heart disease. The first is scar-mediated VT, much like the, as I discussed a second ago, the atrial arrhythmias. You have a patient with an outflow tract patch for tetralogy of fallot and this is going to provide a boundary that will allow for re-entry. This is very different from the failing systemic right ventricle. You can see the systemic right ventricle in this anatomical dissection. It's just such a thin-walled structure, not meant to pump to high pressures and failing in that sense can lead to usually polymorphic ventricular arrhythmias and ventricular fibrillation as opposed to scar-mediated monomorphic VT. Just recognizing as I showed in that diagram that right ventricle is definitely a different beast compared to the LV. It's less muscular and it really relies on the left ventricle for a lot of its forward propulsion of blood. So once that left ventricle starts to fail, really we start to run into a lot of trouble with your right ventricular function. As you know for patients with acquired heart disease, that's if an LVEF is below 35%, they meet criteria in most patients, if certainly with scar-related ischemic heart disease for ICD implantation. Is it the same if your right ventricle is failing? Here we have systemic right ventricles in our congenitally corrected transposition group. It probably is. We can see very few events of sudden cardiac death and ICD therapies in patients whose right ventricular systolic function is better, so 35% and above. If you see those patients with the reduced systemic ventricular function, I would start thinking of primary prevention ICD implantation. Tetralogy, the overriding right ventricle, the VSD, the hypertrophied right ventricle, these are the key elements for our most common complex congenital heart disease. To repair that, you're going to be left with a VSD patch. You're going to have to open the outflow tract patch, cut away the overriding muscle to allow for exit of blood, and this then gets patched. You also have scars related cardiopulmonary bypass, scars in the ventricle itself. Here is an open operative photo of what they can look like with a Gore-Tex patch. With all of that scar in the heart, there's been a lot of work over the years looking at what are the risk factors in this group for sudden death. All of these are significantly related, but these I would take home and these are commonly on boards. If you see this QRS duration at 190 milliseconds, you know that there is very slow conduction in the ventricle, which is going to set that patient up for reentry. VT that's inducible at an EP study is a risk factor and that would be actually polymorphic or monomorphic. Based on that, it would be reasonable to consider primary prevention ICD implant, documented non-sustained VT on a halter, and then because the right ventricle is so reliant on that left ventricle, once the left ventricle starts to fail, it really is a very much more dangerous situation with a higher risk of sudden death and tetralogy. We should follow these patients closely, ambulatory ECG monitoring, exercise them, beta blockers are important and because it's scar related, ablation can be very effective in this group and there is actually a role for avoiding ICDs if it's a single VT which you can ablate, prove bidirectional block and there's nothing inducible afterwards and that's if the right ventricle is not failing. So there are multiple isthmuses that we can see in these patients with congenital heart disease. This was from a case that we did where the isthmus was up here, we were able to entrain the VT that was revolving on this anterior piece of muscle between the pulmonary valve and this outflow tract scar, entrained both sides, ablated from valve to scar and then paced to prove bidirectional block. Most common also is actually involving the VSD patch, but with those kinds of ablations, we and others have shown that bidirectional block is really key if you want to prevent against recurrence. The surgeon can actually do the same thing, freeze these areas afterwards and then we bring them back around 9 months later, 12 months later to check to make sure there is block and the surgeon didn't cause re-entry or cause anitis for re-entry when trying to bomb-proof the heart from re-entrant arrhythmias. But surgical cryoablation is effective and should be considered. So looking at that likelihood of sudden death in Tetralogy of Fallot, if we're following these patients out from repair, it is a late event, but it's a real cause of sudden death and up to 10% in some studies. Epstein's actually, so this is a right-sided heart disease with failed delamination of the tricuspid valve and it's a right ventricular cardiomyopathy as well. A similar kind of trajectory here 20 years afterwards, looking at the likelihood of sudden death in that 10% range. So it's not just Tetralogy, right ventricular disease like Epstein's really need to be aware that this is a real issue for them too. So last section to discuss, moving from then ventricular arrhythmias to stroke. It's a major problem for these patients too. It's 10 to 100-fold higher in this group and there isn't a, for the CHADS-2, CHADS-2-VASc score, these patients were excluded with the development of that schema. So we don't use typically these risk scores for these patients. Those are looking at the older patient with the quiet heart disease, typically with diastolic dysfunction and enlarged left atria. This is a group of patients obviously where the majority of the disease is actually right-sided. Left atrium can be entirely normal even in the Epstein's patients, huge right atria and entirely normal left atrial volume and low risk of clots on the left side potentially. There are not a lot of studies unfortunately, but if you even take the ASDs, our most simple form of congenital heart disease and you look back to the original longitudinal study from the 1990s, that there were 22% of late deaths due to stroke and all of those deaths occurred in patients with atrial fibonatural flutter. So really a real issue for these patients and the societies and AHA, ACC have come up with some proposals. This is a very complex approach to what do we do with anticoagulation that I'm trying to distill down into this slide here. Still, there is a leaning towards moderate complex congenital heart disease. Maybe we should choose warfarin. More and more data is emerging for the direct oral anticoagulants and I have started to switch the majority of my patients to direct oral anticoagulants, obviously not those with mitral stenosis or mechanical heart valves. Simple congenital heart disease and if you take then just that ASD population, maybe we can use CHA2DS2-VASc scores with them. Those are patients who are able to lead a more normal life. They live into their 60s, 70s and beyond and they've been given a chance to develop the same risk factors like diabetes and hypertension and put them at risk for stroke. So either can be used there and that risk schema can be considered. There's another interesting caveat though to the stroke in these patients. So from our cohort of Epstein's, which we looked at and there was about a thousand patients, 10%, 11% had stroke and the mean age was very young. But if you look at the predictors here, the predictors here are migraine, odds ratio of 2.2 and ASD. Both of these suggesting paradoxical emboli as being the source or the mechanism for their stroke and very different from the CHA2DS2-VASc risk score. So be aware if there is an atrial shunt and there's slow flow in the right heart in some of these patients, they are really more likely to be at risk of paradoxical emboli. So I'm going to stop there with these take-home points. As mentioned, this is just a broad overview for you to be aware of the differences in some of these patients that you'll see on their telemetry strips and in the ER. They're not always coming in with faster heart rates because they have congenital heart disease. I'm always looking to see can we unmask an atrial tachycardia that's re-entering with a slower cycle length. Because it's re-entry, we really want to adopt an anti-arrhythmic approach. Avianodal blockers are very ineffectual in this context. Class III drugs are going to be your go-to drugs or ablation. Pacing, that's the intracardiac shunts to be aware of. Imaging, venograms, anything that's going to develop on your leads can cross over and lead to stroke. Sudden death, be aware of the very broad disease QRS and associated alveolar dysfunction. For that patient with a normal RV function, discreet scar-related VT ablation is a really excellent option in making sure that you're going to check for bidirectional block afterwards. I would err on the side of anticoagulation for these patients. It's really difficult to predict who and when and what. They have such a high incidence of stroke at a young age. Be aware of the paradoxical emboli and the leads that are sitting there. Maybe there's an ASD or a large PFO. Leading towards anticoagulation. Thank you very much for your attention. I hope that helps with regards to the exam and practice.

congenital heart disease

arrhythmias

cardiac electrophysiology

atrial arrhythmias

ablation techniques

anticoagulation therapy

heart rhythm board exam