Our next speaker is going to be Complex Anatomy Can Still Produce Simple Reentrant Substrates from Mike Epstein, so thanks. Thank you, Dr. Creeble and Dr. Cannon, and thank you to the Programming Committee for giving me the opportunity to talk to you today. The assigned title of my talk is Complex Anatomy Can Still Produce Simple Reentrant Substrates. I've taken the liberty to make a slight modification to this title without any change in the intent intended spirit. Instead, I'll be discussing that simple reentrant substrates can occur in the setting of complex anatomy, and rather than present a sweeping, rapid review of multiple such arrhythmias recurring in a vast array of multiple acquired and congenital anatomic variants, I will focus this talk on just two simple arrhythmias occurring in a single anatomic setting, and I have no relationships to disclose. The simple reentrant substrates that I will discuss when occurring in the setting of a structurally normal heart can be easily ablated at low risk with a high rate of acute success and a low rate of arrhythmia recurrence. The first such simple reentrant substrate is avenodal reentry tachycardia. Techniques for the treatment of avenodal reentry tachycardia with slow pathway modification are well established. The presence of dual avenodal physiology is usually documented, after which the arrhythmia is induced and the mechanism confirmed. Slow inputs into the avenode are targeted with the delivery of radiofrequency or cryoenergy within the posterior third of the triangle of Koch, ideally at a location recording a small atrial electrogram and large ventricular electrogram with a high frequency component at the end of the atrial electrogram believed to represent a slow pathway potential. When radiofrequency energy is used, the development of mild to moderately accelerated junctional acceleration supports the choice of ablation location. Long-term success is likely with complete elimination of anti-grade slow pathway conduction or modification to the point that only single slow fast avenodal echo beats are inducible. The second simple reentrant substrate that I would like to discuss is cavotrichospinous misdependent intraatrial reentry tachycardia or IART, commonly referred to as atrial flutter when occurring in the setting of normal heart structure. With this arrhythmia, a classic sawtooth pattern of atrial activity or flutter wave is noted in the inferior leads on surface electrocardiogram. In its typical form, these flutter waves are negative, corresponding to counterclockwise activation around the tricuspid valve annulus. Confirmation at the reentrant circuit utilizes the cavotrichospidismus can be performed with pacing within this region, documenting both concealed entrainment and approximation of the post-pacing interval with the tachycardia cycle length. A series of ablation lesions from the tricuspid valve annulus, the inferior vena cava are created, after which the presence of bidirectional block across the cavotrichospidismus can be documented. My chosen complex congenital heart lesion is detransposition of the great arteries where the right ventricle pumps deoxygenated systemic venous blood to the aorta and the left ventricle pumps oxygenated pulmonary venous blood to the pulmonary artery. In its native form, the triangle of Koch and cavotrichospidismus are located within the right atrium, as is in the case of the structurally normal heart. This would continue to be true following the arterial switch operation, which was routinely performed as surgical correction today. However, from the late 1950s to the early 1980s, the atrial switch, including the mustard and setting operations were the palliative procedures of choice, redirecting systemic and pulmonary venous return through a complex system of intraatrial baffles to restore normal physiologic circulation. These procedures have profound consequences with regards to the anatomic fate of both the triangle of Koch and cavotrichospidismus, as well as the ablative treatment of avian oval reentry tachycardia and CTI-dependent IART. The anatomic fate of both the triangle of Koch and cavotrichospidismus following the mustard and setting procedures are well illustrated in this diagram published by Ron Cantor. The inferior baffle of the mustard procedure bisects the cavotrichospidismus depicted in red to various degrees, depending upon whether or not the coronary sinus os was left on the systemic or pulmonary venous side of the baffle. A more anteriorly positioned baffle, seen here in the lower left, allowed for drainage of deoxygenated coronary sinus blood into the systemic venous atrium. However, required the placement of sutures within the region of slow inputs to the AV node, highlighted in light blue. In an effort to minimize the risk for AV conduction injury, many surgeons chose to secure the baffle more posteriorly, as seen here in the upper left, where the coronary sinus drains into the pulmonary venous atrium. This was the approach that was standardly utilized in the setting procedure. A third strategy, seen here in the upper right, was to anchor the baffle between these two extremes, with suture closure of the coronary sinus os and partial unroofing of the coronary sinus within the systemic venous atrium. All three surgical strategies rendered the AV node, depicted in dark blue, and the his bundle left-sided structures. This cartoon by Paul Carey nicely demonstrates how the cavotrichospidismus is bisected by the atrial switch procedure. In this example, with the baffle secured posterior to the coronary sinus os. Portions of the cavotrichospidismus are present on both sides of the baffle. Processing the pulmonary venous atrium following the atrial switch can be performed either via retrogradiotic approach or a transbaffle approach, either crossing a preexisting baffle leak that's fortuitously positioned or by direct puncture. The transbaffle approach affords greater catheter stability and maneuverability and minimizes the potential risk for hemodynamic instability when you can potentially stent open the systemic AV valve in both the setting of supraventricular tachycardia and diminished systemic right ventricular systolic function. Here is a how-to list on slow pathway modification for AVNRT in the setting of the mustered or setting patient. Careful preparation should be performed, including review of the operative record and images associated with echocardiographic, CT, and or MRI studies. The location of the coronary sinus os, vis-a-vis the inferior baffle, should be deciphered if possible. For if the true coronary sinus os is posterior to the inferior baffle, then a substantial portion of the posterior third of the triangle of cope may remain within the systemic venous atrium. However, ablation within the pulmonary venous atrium is almost universally required for permanent ablation success. The diagnosis of AV nodal reentry tachycardia should be established using standard electrophysiologic principles and procedures, following which access should be gained into the pulmonary venous atrium via one of the methods previously discussed. The triangle of cope should be defined carefully with the recording of a his bundle electrogram or his cloud, engagement of the coronary sinus os if possible, and the marking or tagging of the tricuspid valve annulus. The region inferior to the his bundle should be targeted, looking for the desired one to three or one to four atrial to ventricular electrogram amplitude ratio, as well as for the presence of a slow pathway potential. If retrograde slow pathway conduction is present, the atrial insertion of the slow pathway could also be mapped as confirmation. Ideally, one should see mild to moderately accelerated junctional acceleration with persistence of retrograde fast pathway conduction with radio frequency energy delivery or selective block and antegrade slow pathway conduction with cryo energy delivery. A number of small series and case reports on AVNRT ablation following the atrial switch operation for detransposition of the great arteries have been published over the years, using both radio frequency and cryo energy with excellent acute success rates and minimal complications, with only one reported case of persisting complete AV block with radio frequency energy delivered via retrograde approach. No obvious tachycardia recurrences were reported with short to medium term follow-up. Here is an example of slow pathway modification for AV nodal reentry tachycardia following a mustard operation from a series published by Chalandra Upadhyay. On the left is an LA-Ocado image, showing portions of both the systemic and pulmonary venous atria, with the his bundle and left bundle branch depicted in yellow and sites of radio frequency ablation predicted in red. The slow pathway region was located inferior to the his bundle and anterior to the coronary sinus and was reached via transeptal puncture. On the right here is the electrogram recorded at the site of ablation success, noting a small atrial component, a large ventricular component, and possibly a small pathway potential. Shifting gears towards the ablation of CTI-dependent IART, careful pre-procedure preparation is again critical. An in-depth review of the operative record and all imaging should be performed, once again paying careful attention to the location of the coronary sinus os, vis-a-vis the inferior baffle, which will help to determine how much of the cavernous tracuspidismus is sequestered within the pulmonary venous atrium. The arrhythmia should be induced and mechanism confirmed using standard principles. And if utilizing a three-dimensional mapping system, an electroanatomic map should be made within the systemic venous atrium. Of critical importance is establishing that the cavernous tracuspidismus is within the tachycardia circuit using standard entrainment techniques. The next step is the creation of an ablation line from the base of the baffle to the IBC. This is ideally performed during IART, where you can observe for cycle length lengthening and possible tachycardia termination. Regardless of the effect of the ablation on the systemic venous side of the baffle, the line should be completed from the tracuspid valve annulus to the baffle after gaining access into the pulmonary venous atrium. Establishment of ablation success can be performed by assessing for re-inducibility as well as the presence of bidirectional block across the cavernous tracuspidismus. Published results of ablation of CTI-dependent IART in the atrial switch population consists of a number of small series documenting reasonable efficacy and minimal number of complications and a handful of recurrences over a short to medium-length follow-up period. Cryo-frequency energy, sometimes with saline irrigation, was exclusively used as opposed to the AVNRT group where cryoablation was preferred by some operators. I would like to wrap up with a few examples. This electroanatomic map of the pulmonary venous atrium published by Galati et al. notes counterclockwise activation around the tracuspid valve annulus. Entrainment mapping performed within the cavernous tracuspidismus notes concealed entrainment as well as a post-pacing interval nearly identical to the tachycardia cycle length. This electroanatomic map merged with a CT image published by Wu et al. notes counterclockwise activation around the tracuspid valve annulus and side-by-side images of both the systemic venous atrium here on the left and pulmonary venous atrium here on the right. The dark red dots represent successful radiofrequency ablation within the cavernous tracuspidismus located on the pulmonary venous side of the baffle. Finally, this series of in-site images published by Paul Carey notes a clockwise peritracuspid valvular circuit utilizing the cavernous tracuspidismus. Successful radiofrequency ablation, the light blue dots, required the placement of RF energy both within the pulmonary venous atrium color-coded purple and the systemic venous atrium color-coded blue. Thank you for your attention. I look forward to your comments and answering your questions. That was a great talk. One of the ones I want to bring up is the sending operation. One of the things we noticed is after the sending operation, a lot of times they're scarred back by the right pulmonary veins where the anastomosis is created. And we've seen a number of cases where they've either recurred, we've had to go back and ablate that area, or we actually see that like a dual loop mechanism involving that area at the first ablation. And so we almost basically empirically ablate that now if there's a conduction gap between that scar and then the septal sort of baffle scar. You think it's the same, the CTI dependent form of ART, which is so common in this group? Well, no, we see the CTI, but we also see the secondary circuit in the back wall, specifically in settings it seems like for some reason. And the Galati paper, I think. I mean, a lot of the studies show that the big macro reentry circuit in this population involves the CTI area. And then it's more of the more focal reentrant tachycardias that we see near suture lines, like what you're describing. So for the muster, for instance, atriotomy circuits is the secondary circuit, and the sending is that posterior wall. So it's just interesting that it seems like it's related to the surgery specifically. Do you have a preferred mapping system for mapping these complex hearts, or do you think one is superior to the other, or are they all about the same? The only one I have that I have access to is the CARTO system, so. That's the one you use. That's the one I use. Actually, I prefer to give a comment for this, because I have access to both, Nevex and CARTO. I think, at the moment, I'm worried that the AV node would be a problem for me in advance. Before I do this study, I would use Nevex, because I can use cryo. The use of cryo and CARTO is very difficult. You have to sheet the system, and you can't really put the lesions on, and that's the reason I use Nevex for these patients. Any more questions? Okay. Thank you.

simple reentrant substrates

complex anatomy

arrhythmias

slow pathway modification

ablation