Risk of infective endocarditis after hybrid melody mitral valve replacement in infants: the French experience.

OBJECTIVES: Surgical management of mitral valve disease is challenging in infants <1 year old. We aimed at reviewing the French experience with Melody mitral valve replacement in critically ill infants. METHODS: A retrospective cohort study reporting the French experience with Melody mitral valve replacement. RESULTS: Seven symptomatic infants [complete atrioventricular septal defect (n = 4, Down syndrome: n = 3), hammock valve (n = 3)] underwent Melody mitral valve replacement [age: 3 months (28 days to 8 months), weight: 4.3 kg (3.2-6.4 kg)] because of severe mitral valve regurgitation (6) or mixed valve disease (1) and 14 mm (11-16 mm) mitral valve annulus. In 2 patients whose valve was felt irreparable, Melody mitral valve replacement was performed straightaway. The others underwent 2 (1-3) previous attempts of valve repair; 3 were on extracorporeal membrane oxygenation. Melody mitral valve replacement led to competent valve and low gradient [3 mmHg, (1-4 mmHg)]. One patient died 3 days post-implant from extracorporeal membrane oxygenation-related stroke. Of the 6 discharged home patients, 3 (50%) were readmitted for a definite diagnosis (1) or high suspicion (2) of infective endocarditis, of which 2 died. Over the follow-up, 1 underwent balloon expansions of the valve at 9- and 16-months post-implant, and mechanical mitral valve replacement at 2 years; another is currently planned for transcatheter Melody valve dilation. CONCLUSIONS: Melody mitral valve replacement may be considered in selected infants with small mitral valve annulus as an alternative to mechanical mitral valve replacement. Our experience highlights a high-risk of late infective endocarditis that deserves further consideration.

Contrast-free left atrial appendage occlusion in patients using the LAMBRE™ device.

BACKGROUND: Advances in imaging have led to procedural optimization of left atrial appendage closure (LAAC). Contrast-free approaches, guided merely by echocardiography, have been established, however data on this topic remains scarce. In this analysis, we assessed contrast-free procedural results with the LAMBRE LAAC device. METHODS: The multicenter retrospective BoBoMa (Bonn/Bordeaux/Mainz)-Registry included a total of 118 patients that underwent LAAC with LAMBRE devices omitting contrast-dye. Baseline and echocardiographic characteristics as well as intra- and postprocedural complications and outcomes were assessed. RESULTS: Patients were at a mean age of 77.5 ± 7.5 years with high thromboembolic and bleeding risk (CHADS-VASc-score 4.6 ± 1.4, HAS-BLED-score 3.7 ± 1.0, respectively). Renal function was impaired with a mean glomerular filtration rate (GFR) of 50 ± 22 ml/min. Mean procedural time was 47.2 ± 37.5  minutes with a mean radiation dose of 4.75 ± 5.25 Gy*cm2. Device success, defined as proper deployment in a correct position, was achieved in 97.5% (115/118) of cases with repositioning of the occluder in 7.6% (9/118) and resizing in 3.4% (4/118) of cases. No relevant peri-device leakage (>3 mm) was observed with 42% of occluders being implanted in an ostial position. Periprocedural complications occurred in 6.8% (8/118) of cases, including two cases of device embolization and one case of clinically-relevant pericardial effusion requiring surgical intervention. Other complications included pericardial effusion (2.5%, 3/118) and vascular access site complications (1.7%, 2/118). CONCLUSION: Echocardiography-guided contrast-free LAAC using the LAMBRE device is safe and feasible. Further prospective studies including the direct comparison of devices as well as imaging techniques are warranted in contrast-free LAAC.

From Crafoord's End-to-End Anastomosis Approach to Percutaneous Interventions: Coarctation of the Aorta Management Strategies and Reinterventions.

First described in 1760 by the anatomist Morgagni, coarctation of the aorta (CoA) is a congenital heart defect characterized by narrowing the aorta, typically distal to the left subclavian artery. It accounts for approximately 5-8% of all congenital heart diseases, with an incidence estimated at 4 per 10,000 live births. In 1944, the Swedish surgeon Clarence Crafoord achieved the first successful surgical CoA repair by performing an aortic end-to-end anastomosis on two patients aged 12 and 27 years old. Presently, the most prevalent techniques for surgical repair, particularly in infants and neonates with isolated coarctation, involve resection with end-to-end anastomosis (EEA) and the modified Crafoord technique (extended resection with end-to-end anastomosis (EEEA)). Subclavian flap aortoplasty (SCAP) is an alternative surgical option for CoA repair in patients under two years of age. In cases where the stenosis extends beyond resection and end-to-end anastomosis feasibility, patch aortoplasty (PP) employing a prosthetic patch can augment the stenotic region, especially for older patients. Despite advances in pediatric cardiology and cardiac surgery, recoarctation remains a significant concern after surgical or interventional repair. This comprehensive review aims to provide a thorough analysis of coarctation management, covering the pioneering techniques introduced by Crafoord using end-to-end anastomosis and now extending to the contemporary era marked by percutaneous interventions as well as the recoarctation rate associated with each type.

Transcatheter Closure of Superior Sinus Venosus Defects.

Superior sinus venosus defect is a communication between the right and left atrium located above the upper margin of the oval fossa, immediately inferior to the junction of the superior vena cava and the right atrium. It is systematically associated with partial anomalous pulmonary venous drainage, especially of the right upper pulmonary vein. Surgical repair has been the gold standard approach to close that defect. Introduced in 2014, percutaneous closure has gradually become a safe and effective alternative to surgery in carefully selected patients, although worldwide experience remains limited. This article provides an appraisal of the patients' selection process and a step-by-step description of the procedure as well as a comprehensive review of its outcomes.

Lympho-hematopoietic malignancies risk after exposure to low dose ionizing radiation during cardiac catheterization in childhood.

Pediatric patients with congenital heart disease (CHD) often undergo low dose ionizing radiation (LDIR) from cardiac catheterization (CC) for the diagnosis and/or treatment of their disease. Although radiation doses from a single CC are usually low, less is known about the long-term radiation associated cancer risks. We aimed to assess the risk of lympho-hematopoietic malignancies in pediatric CHD patients diagnosed or treated with CC. A French cohort of 17,104 children free of cancer who had undergone a first CC from 01/01/2000 to 31/12/2013, before the age of 16 was set up. The follow-up started at the date of the first recorded CC until the exit date, i.e., the date of death, the date of first cancer diagnosis, the date of the 18th birthday, or the 31/12/2015, whichever occurred first. Poisson regression was used to estimate the LDIR associated cancer risk. The median follow-up was 5.9 years, with 110,335 person-years. There were 22,227 CC procedures, yielding an individual active bone marrow (ABM) mean cumulative dose of 3.0 milligray (mGy). Thirty-eight incident lympho-hematopoietic malignancies were observed. When adjusting for attained age, gender and predisposing factors to cancer status, no increased risk was observed for lympho-hematopoietic malignancies RR/mGy = 1.00 (95% CI: 0.88; 1.10). In summary, the risk of lympho-hematopoietic malignancies and lymphoma was not associated to LDIR in pediatric patients with CHD who undergo CC. Further epidemiological studies with greater statistical power are needed to improve the assessment of the dose-risk relationship.

Predictors of Clinical Success After Transcatheter Paravalvular Leak Closure: An International Prospective Multicenter Registry.

BACKGROUND: Transcatheter closure of a symptomatic prosthetic paravalvular leak (PVL) is feasible, but there is presently no conclusive evidence to show consistent efficacy. We aimed to identify predictors of clinical success after transcatheter PVL closure. METHODS: Consecutive patients referred to 24 European centers for transcatheter PVL closure in 2017 to 2019 were included in a prospective registry (Fermeture de Fuite ParaProthétique, FFPP). Clinical success was absence of any of the following within 1 month: re-admission for heart failure, blood transfusion, open-heart valvular surgery, and death. RESULTS: We included 216 symptomatic patients, who underwent 238 percutaneous PVL closure procedures on the mitral (64.3%), aortic (34.0%), or tricuspid (1.7%) valve. Symptoms were heart failure, hemolytic anemia, or both in 48.9%, 7.8%, and 43.3% of patients, respectively. One, 2, and 3 leaks were treated during the same procedure in 69.6%, 26.6%, and 3.8% of patients, respectively. The PVL was pinpoint or involved 1/8 or 1/4 of the valve circumference in 18.6%, 52.4%, and 28.1% of cases, respectively. The most frequently used devices were the Vascular Plug 3, Ventricular Septal Defect Occluder, Vascular Plug 2, and Paravalvular Leak Device (45.0%, 16.6%, 14.2%, and 13.6% of cases, respectively). Successful device(s) implantation with leak reduction to ≤grade 2 was obtained in 85.0% of mitral and 91.4% of aortic procedures, respectively (P=0.164); with major periprocedural adverse event rates of 3.3% and 1.2%, respectively (P=0.371); and clinical success rates of 70.3% and 88.0%, respectively (P=0.004). By multivariate analysis, technical failure, mechanical valve, and hemolytic anemia were independently associated with absence of clinical success (odds ratios [95% CIs], 7.7 [2.0-25.0]; P=0.002; 3.6 [1.1-11.1]; P=0.036; and 3.7 [1.2-11.9]; P=0.025; respectively). CONCLUSIONS: Transcatheter PVL closure is efficient and safe in symptomatic patients but is associated with a lower clinical success rate in patients with hemolysis and/or a mechanical valve. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifiers: NCT05089136.

The pivotal role of tricuspid regurgitation in the failing systemic right ventricle: The "chicken and egg story".

Systemic right ventricle (SRV) is commonly encountered in patients with congenital heart disease. This nomenclature includes diseases with different anatomic features, adaptation and clinical phenotypes, and has a variable - but overall guarded - prognosis. Right ventricular fibromuscular architecture, shape, adaptation to overload conditions, rhythmic disorders and - most of all - tricuspid regurgitation (TR) contribute to the pathophysiology of SRV failure. The pivotal role of TR is complex as it is due to both the intrinsic abnormalities of the valve (specific to each phenotype) and the consequence of SRV dilation and failure. Medical therapy has not been equivocally proven to be effective for TR. Surgery (valve repair or replacement) has shown conflicting long-term results, mainly dependent on preoperative SRV function. Thus, other management options have been proposed to improve SRV function and valve competency, such as early anatomical correction, pulmonary banding, resynchronization therapy and valvular edge-to-edge percutaneous repair. The aim of this review is to discuss the mechanisms of TR and SRV failure, as well as the available therapeutic options.

Renaissance of Cardiac Imaging to Assist Percutaneous Interventions in Congenital Heart Diseases:The Role of Three-Dimensional Echocardiography and Multimodality Imaging.

Percutaneous interventions have completely refashioned the management of children with congenital heart diseases (CHD) and the use of non-invasive imaging has become the gold standard to plan and guide these procedures in the modern era. We are now facing a dual challenge to improve the standard of care in low-risk patients, and to shift our strategies from the classic open chest surgery to imaging-guided percutaneous interventions in high-risk patients. Such rapid evolution of ultrasound technologies over the last 20 years have permitted the integration of transthoracic, transesophageal and intracardiac echocardiography into the interventional workflow to improve image guidance and reduce radiation burden from fluoroscopy and angiography. Specifically, miniaturization of transesophageal probe and advances in three-dimensional (3D) imaging techniques have enabled real-time 3D image guidance during complex interventional procedure, In addition, multimodality and fusion imaging techniques harness the strengths of different modalities to enhance understanding of anatomical and spatial relationship between different structures, improving communication and coordination between interventionalists and imaging specialists. In this review, we aim to provide an overview of 3D imaging modalities and multimodal fusion in procedural planning and live guidance of percutaneous interventions. At the present times, 3D imaging can no longer be considered a luxury but a routine clinical tool to improve procedural success and patient outcomes.

Radiation dose during catheter ablation in children using a low fluoroscopy frame rate.

BACKGROUND: Catheter ablation (CA) in children using fluoroscopy carries risks inherent to ionizing radiation exposure. AIMS: The objective of this study was to demonstrate the feasibility of using low frames rate during ablation in children to maximally decrease radiation dose. METHODS: Hundred sixty eight successive patients<18 years of age undergoing CA performed under a 3.75 frames/second rate were retrospectively included. Demographics, procedural and dosimetry data were analysed. The effective dose (ED) was evaluated in a subgroup of 14 patients. RESULTS: Median age and weight were 15 years and 54kg, 72% had WPW, 10% AV node reentrant tachycardia, 10% ventricular tachycardia (atrial tachycardia, flutter and atrial fibrillation for the other cases). Acute success was achieved in 98.5% without any complication. Median procedure and fluoroscopy duration were 120 and 16minutes. Median Dose Area Product (DAP) and Air Kerma were 2.46Gy.cm2 and 18 mGy respectively (2Gy.cm2 and 15 mGy for WPW ablation). A significant reduction of median DAP was noted over the years for WPW, from 3.1Gy.cm2 in 2011 to 1.4 in 2019. Median estimated ED was 0.19 mSv (0.03 to 1.64), falling into the range of yearly normal natural irradiation or caused by leasure or professional activity. CONCLUSION: Low frame rate fluoroscopy is a highly effective and safe approach in decreasing radiation exposure during CA in children without altering the success rate of the procedure. ED is low, similar to natural/leisure irradiation. This approach can be considered a good alternative to 3D-based procedures in terms of efficiency and radiation issues, at least for WPW ablations.

HRAS germline mutations impair LKB1/AMPK signaling and mitochondrial homeostasis in Costello syndrome models.

Germline mutations that activate genes in the canonical RAS/MAPK signaling pathway are responsible for rare human developmental disorders known as RASopathies. Here, we analyzed the molecular determinants of Costello syndrome (CS) using a mouse model expressing HRAS p.G12S, patient skin fibroblasts, hiPSC-derived human cardiomyocytes, a HRAS p.G12V zebrafish model, and human fibroblasts expressing lentiviral constructs carrying HRAS p.G12S or HRAS p.G12A mutations. The findings revealed alteration of mitochondrial proteostasis and defective oxidative phosphorylation in the heart and skeletal muscle of CS mice that were also found in the cell models of the disease. The underpinning mechanisms involved the inhibition of the AMPK signaling pathway by mutant forms of HRAS, leading to alteration of mitochondrial proteostasis and bioenergetics. Pharmacological activation of mitochondrial bioenergetics and quality control restored organelle function in HRAS p.G12A and p.G12S cell models, reduced left ventricle hypertrophy in CS mice, and diminished the occurrence of developmental defects in the CS zebrafish model. Collectively, these findings highlight the importance of mitochondrial proteostasis and bioenergetics in the pathophysiology of RASopathies and suggest that patients with CS may benefit from treatment with mitochondrial modulators.

Exposure to low-dose ionising radiation from cardiac catheterisation and risk of cancer: the COCCINELLE study cohort profile.

PURPOSE: The COCCINELLE study is a nationwide retrospective French cohort set up to evaluate the risk of cancer in patients who undergone cardiac catheterisation (CC) procedures for diagnosis or treatment of congenital heart disease during childhood. PARTICIPANTS: Children who undergone CC procedures from 1 January 2000 to 31 December 2013, before the age of 16 in one of the 15 paediatric cardiology departments which perform paediatric CC in mainland France were included. The follow-up started at the date of the first recorded CC procedure until the exit date, that is, the date of death, the date of first cancer diagnosis, the date of the 18th birthday or the 31 December 2015, whichever occurred first. The cohort was linked to the National Childhood Cancer Registry to identify patients diagnosed with cancer and with the French National Directory for the Identification of Natural Persons to retrieve the patients' vital status. FINDINGS TO DATE: A total of 17 104 children were included in the cohort and followed for 110 335 person-years, with 22 227 CC procedures collected. Among the patients, 81.6% received only one procedure. Fifty-nine cancer cases were observed in the cohort. Standardised incidence ratios (SIRs) were increased for all-cancer (SIR=3.8, 95% CI: 2.9 to 4.9), leukaemia (SIR=3.3, 95% CI: 2.0 to 5.4), lymphoma (SIR=14.9, 95% CI: 9.9 to 22.5) and solid cancers excluding central nervous system (CNS) tumours (SIR=3.3, 95% CI: 2.0 to 5.5) compared with the general population. FUTURE PLANS: Dose reconstruction is currently underway to estimate individual cumulative doses absorbed to relevant organs, including red bone marrow and brain for respectively haematologic disorders and CNS tumours risk estimation. A dose-response analysis will be conducted with consideration to confounding factors such as age at exposure, gender, predisposing factors to cancer and other sources of medical diagnostic low-dose ionising radiation.

Health-related quality of life and physical activity in children with inherited cardiac arrhythmia or inherited cardiomyopathy: the prospective multicentre controlled QUALIMYORYTHM study rationale, design and methods.

BACKGROUND: Advances in paediatric cardiology have improved the prognosis of children with inherited cardiac disorders. However, health-related quality of life (QoL) and physical activity have been scarcely analysed in children with inherited cardiac arrhythmia or inherited cardiomyopathy. Moreover, current guidelines on the eligibility of young athletes with inherited cardiac disorders for sports participation mainly rely on expert opinions and remain controversial. METHODS: The QUALIMYORYTHM trial is a multicentre observational controlled study. The main objective is to compare the QoL of children aged 6 to 17 years old with inherited cardiac arrhythmia (long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, or arrhythmogenic right ventricular dysplasia), or inherited cardiomyopathy (hypertrophic, dilated, or restrictive cardiomyopathy), to that of age and gender-matched healthy subjects. The secondary objective is to assess their QoL according to the disease's clinical and genetic characteristics, the level of physical activity and motivation for sports, the exercise capacity, and the socio-demographic data. Participants will wear a fitness tracker (ActiGraph GT3X accelerometer) for 2 weeks. A total of 214 children are required to observe a significant difference of 7 ± 15 points in the PedsQL, with a power of 90% and an alpha risk of 5%. DISCUSSION: After focusing on the survival in children with inherited cardiac disorders, current research is expanding to patient-reported outcomes and secondary prevention. The QUALIMYORYTHM trial intends to improve the level of evidence for future guidelines on sports eligibility in this population. Trial registration ClinicalTrials.gov Identifier: NCT04712136, registered on January 15th, 2021 ( https://clinicaltrials.gov/ct2/show/NCT04712136 ).

Comparison of Two Percutaneous Atrial Septal Defect Occluders for Device Healing and Nickel Release in a Chronic Porcine Model.

AIMS: To investigate the healing process and nickel release of the Hyperion occluder (Comed BV, Netherlands), as compared to the Amplatzer septal occluder (ASO) (St. Jude Medical Inc., St. Paul, MN, USA) in a chronic swine model. BACKGROUND: Some long-term complications occurring after percutaneous atrial septal defect (ASD) closure may be partially associated with an inappropriate healing of the device and increased nickel release. There is no direct comparative study of different occluders for healing and nickel release. METHODS: After percutaneous ASD creation, 12 pigs were implanted with 15 mm Hyperion (n = 6) and 15 mm ASO (n = 6) devices. After 1 month (n = 3 for each device) and 3 months (n = 3 for each device) of follow-up, device explantation was performed and healing was assessed using histopathological workup. Systemic and tissular nickel release was performed. RESULTS: Implantation was successful in 100% without complications. Device coverage was observed as early as 1 month after implantation and was almost complete after 3 months. A granulation tissue with a predominantly mononuclear inflammatory reaction was observed in contact with nitinol wires while an inflammatory reaction was seen in contact with textile fibers. We found no statistically significant difference between the 2 devices whether for histological grading scores or systemic nickel release, regardless to follow-up duration. CONCLUSIONS: In this preclinical study, we demonstrated that Amplatzer septal occluder and Hyperion occluder were not significantly different for device healing and nickel release processes.

Position paper concerning the competence, performance and environment required for the practice of ablation in children and in congenital heart disease.

The population of patients with congenital heart disease (CHD) is continuously increasing, and a significant proportion of these patients will experience arrhythmias because of the underlying congenital heart defect itself or as a consequence of interventional or surgical treatment. Arrhythmias are a leading cause of mortality, morbidity and impaired quality of life in adults with CHD. Arrhythmias may also occur in children with or without CHD. In light of the unique issues, challenges and considerations involved in managing arrhythmias in this growing, ageing and heterogeneous patient population and in children, it appears both timely and essential to critically appraise and synthesize optimal treatment strategies. The introduction of catheter ablation techniques has greatly improved the treatment of cardiac arrhythmias. However, catheter ablation in adults or children with CHD and in children without CHD is more technically demanding, potentially causing various complications, and thus requires a high level of expertise to maximize success rates and minimize complication rates. As French recommendations regarding required technical competence and equipment are lacking in this situation, the Working Group of Pacing and Electrophysiology of the French Society of Cardiology and the Affiliate Group of Paediatric and Adult Congenital Cardiology have decided to produce a common position paper compiled from expert opinions from cardiac electrophysiology and paediatric cardiology. The paper details the features of an interventional cardiac electrophysiology centre that are required for ablation procedures in adults with CHD and in children, the importance of being able to diagnose, monitor and manage complications associated with ablations in these patients and the supplemental hospital-based resources required, such as anaesthesia, surgical back-up, intensive care, haemodynamic assistance and imaging. Lastly, the need for quality evaluations and French registries of ablations in these populations is discussed. The purpose of this consensus statement is therefore to define optimal conditions for the delivery of invasive care regarding ablation of arrhythmias in adults with CHD and in children, and to provide expert and - when possible - evidence-based recommendations on best practice for catheter-based ablation procedures in these specific populations.

Transcatheter ductus arteriosus stenting in paediatric cardiology: Indications, results and perspectives.

Stenting the arterial duct emerged in the early 1990s as an alternative to a variety of surgical interventions in neonates with a duct-dependent pulmonary or systemic circulation complex defect. Furthermore, palliative ductal stenting has been applied in older children with severe suprasystemic pulmonary arterial hypertension, as an alternative to surgical shunts, such as Potts anastomosis. Early results of this technique were discouraging, but by learning from the failures of the past, ductal stenting has become a reliable palliative therapy. In this review, we aim to describe the historical evolution of ductal stenting, its different clinical applications and outcomes, and future perspectives for this strategy in congenital cardiac catheterization.

Assessment of the healing process after percutaneous implantation of a cardiovascular device: a systematic review.

The healing process, occurring after intra-cardiac and intra-vascular device implantation, starts with fibrin condensation and attraction of inflammatory cells, followed by the formation of fibrous tissue that slowly covers the device. The duration of this process is variable and may be incomplete, which can lead to thrombus formation, dislodgement of the device or stenosis. To better understand this process and the neotissue formation, animal models were developed: small (rats and rabbits) and large (sheep, pigs, dogs and baboons) animal models for intra-vascular device implantation; sheep and pigs for intra-cardiac device implantation. After intra-vascular and intra-cardiac device implantation in these animal models, in vitro techniques, i.e. histology, which is the gold standard and scanning electron microscopy, were used to assess the device coverage, characterize the cell constitution and detect complications such as thrombosis. In humans, optical coherence tomography and intra-vascular ultrasounds are both invasive modalities used after stent implantation to assess the structure of the vessels, atheroma plaque and complications. Non-invasive techniques (computed tomography and magnetic resonance imaging) are in development in humans and animal models for tissue characterization (fibrosis), device remodeling evaluation and device implantation complications (thrombosis and stenosis). This review aims to (1) present the experimental models used to study this process on cardiac devices; (2) focus on the in vitro techniques and invasive modalities used currently in humans for intra-vascular and intra-cardiac devices and (3) assess the future developments of non-invasive techniques in animal models and humans for intra-cardiac devices.

Ultra-High-Density Activation Mapping to Aid Isthmus Identification of Atrial Tachycardias in Congenital Heart Disease.

OBJECTIVES: A new electroanatomic mapping system (Rhythmia, Boston Scientific, Marlborough, Massachusetts) using a 64-electrode mapping basket is now available; we systematically assessed its use in complex congenital heart disease (CHD). BACKGROUND: The incidence of atrial arrhythmias post-surgery for CHD is high. Catheter ablation has emerged as an effective treatment, but is hampered by limitations in the mapping system's ability to accurately define the tachycardia circuit. METHODS: Mapping and ablation data of 61 patients with CHD (35 males, age 45 ± 14 years) from 8 tertiary centers were reviewed. RESULTS: Causes were as follows: Transposition of Great Arteries (atrial switch) (n = 7); univentricular physiology (Fontans) (n = 8); Tetralogy of Fallot (n = 10); atrial septal defect (ASD) repair (n = 15); tricuspid valve (TV) anomalies (n = 10); and other (n = 11). The total number of atrial arrhythmias was 86. Circuits were predominantly around the tricuspid valve (n = 37), atriotomy scar (n = 10), or ASD patch (n = 4). Although the majority of peri-tricuspid circuits were cavo-tricuspid-isthmus dependent (n = 30), they could follow a complex route between the annulus and septal resection, ASD patch, coronary sinus, or atriotomy. Immediate ablation success was achieved in all but 2 cases; with follow-up of 12 ± 8 months, 7 patients had recurrence. CONCLUSIONS: We demonstrate the feasibility of the basket catheter for mapping complex CHD arrhythmias, including with transbaffle and transhepatic access. Although the circuits often involve predictable anatomic landmarks, the precise critical isthmus is often difficult to predict empirically. Ultra-high-density mapping enables elucidation of circuits in this complex anatomy and allows successful treatment at the isthmus with a minimal lesion set.