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Background: Intrinsic myocardial stiffness (MS) is load-independent, unlike most parameters to assess LV systolic and diastolic function. Pre-clinical studies have found good correlation between 1) peak-systolic MS and contractility (or ESPVR); 2) end-diastolic MS and compliance (or EDPVR). Shear wave imaging (SWI) by ultrafast ultrasound imaging allows MS measurement throughout the cardiac cycle. Methods (Fig 1): Five children with LV pressure-overload (LV-PO; 2 aortic stenosis, 3 coarctation) were studied during cardiac catheterization and there were 5 age-matched controls. Interventricular septal MS was measured by SWI every 100ms during the cardiac cycle, pre- and post-balloon dilation. ESPVR and EDPVR were assessed by pressure-volume loops by a pressure catheter and real-time 3D-echo volumes. Results (Fig 2): Peak-systolic MS was higher in LV-PO (22.7±6.7 kPa) than controls (8.4±2.8 kPa; p Conclusions: Non-invasive MS is a load-independent measure of LV systolic contractility and diastolic compliance in children.

Background: Echocardiographic parameters to assess systolic and diastolic RV function are strongly dependent on loading conditions. Myocardial stiffness (MS) is an intrinsic myocardial property that influences both diastolic and systolic cardiac function. MS is independent of loading conditions and pre-clinical studies have demonstrated a correlation between 1) systolic MS and contractility (or ESPVR); 2) end-diastolic MS and compliance (or EDPVR). Shear wave imaging (SWI) by ultrafast ultrasound imaging allows quantitative MS assessment at any time of the cardiac cycle. This noninvasive technique could provide load-independent measure of RV function. Methods (figure 1): Ten children, 5 pulmonary arterial hypertension patients (PAH) undergoing diagnostic right heart catheterization (RHC) were prospectively enrolled as well as 5 age-matched heathy volunteers (HV). MS was assessed at baseline and during FiO2 70%+40ppm NO for the PAH group. MS in the RV free wall using SWI every 100ms during the cardiac cycle. RV-ESPVR and RV-EDPVR were assessed by pressure-volume loops using a pressure catheter and real-time 3D-echo volumes. Results (figure 2): MS increased significatively in systole compared to end-diastole in both groups (p Conclusions: Our preliminary data demonstrate that MS could be a quantitative measure of RV contractility and diastolic compliance of the RV.

Introduction: Diagnosing diastolic dysfunction (DD) non-invasively in children is challenging as no validated pediatric diagnostic algorithm is available. The aim of this study is to use machine learning (ML) to identify a model that integrates echocardiographic measurements to predict invasive hemodynamic markers of DD in children. Methods: We enrolled children with Kawasaki disease, heart transplant, aortic stenosis, and coarctation of the aorta undergoing left heart catheterization. We obtained simultaneous invasive and echo DD measurements. We applied random forest (RF) algorithms to develop separate models for each cath marker (time constant of isovolumic relaxation (Tau), LVEDP, and -dP/dt max) and used demographics, diagnosis, and echo features as inputs. Model approximation was done using a regression tree with the top ranked features of each RF model to improve model interpretability (Figure 1). Spearman correlations were also assessed. Results: 59 children were included. Spearman correlations were low. However, the RF models' adjusted R 2 values in predicting Tau, LVEDP, and -dP/dt max are 0.62, 0.51, and 0.83, respectively. A representative ML-generated tree for LVEDP is shown in Figure 2. The most important features were propagation velocity (Vp) for Tau; E/Vp ratio for LVEDP; and systolic global longitudinal strain rate for -dP/dt max. Model approximation showed that a Vp < 42 cm/s predicted a Tau > 39 ms, and an E/Vp > 2.4 predicted an LVEDP > 13 mmHg. Conclusions: Predicting invasively measured diastolic parameters with echo data may be improved using ML algorithms. Model approximation may help better interpret the complex interactions in ML models.

Background: Little is known about serial changes in the physiology of single ventricle (SV) patients during staged palliation and if HLHS patients differ from the rest. Methods: We analyzed SV patients who had a combined cath with CMR at both the preBCPC and preFontan studies from 2016-2019. Flow contrast mapping used to calculate pulmonary arterial (Qpa) and venous (Qpv) flow. Systemic blood flow (Qs) calculated using [superior vena cava (SVC) flow + descending aortic flow at the level diaphragm]. Cerebral vascular resistance (CVRi) calculated using [ascending aortic pressure (AoP)-right atrial pressure (RAP)/SVC flow]. Systemic vascular resistance (SVR) calculated using [(AoP-RaP)/Qs]. Pulmonary vascular resistance (PVR) was calculated using [(mean PAP - LAP)/Qpv]. Results: 30 patients were found, 10 with HLHS. The BCPC unloaded the heart, EDVi fell from preBCPC to preFontan. From preBCPC to preFontan(Table1): PA flow fell, but was compensated by increased APC flow to keep QpQs~1, PApressure and PVRi fell. Compared to others, the HLHS patients had larger hearts (EDVi) and lower PA but higher APC flow at both preBCPC(Table2)and preFontan(Table3). By preFontan, HLHS patients had worse function: higher ESVi, lower EF. Conclusion: QpQs ~1 is maintained by increase in APC flow. HLHS hearts are larger and deteriorate progressively.

Introduction: Melody™ valve in the mitral position has been described for use in infants. Hypothesis: Melody™ valve (Medtronic) in the mitral position would improve survival compared to mechanical mitral valves for young children. Methods: Charts were retrospectively reviewed for children who had undergone a Melody™ valve insertion (MEL) between 2014 and 2020. MEL were case-matched by age and weight to those with a mechanical mitral valve (MECH). We compared transplant free survival and cumulative incidence of re-intervention. A sub-analysis was performed for children Results: Eleven children underwent Melody™ mitral valve replacement (MVR) over the study period. Age was 157 (104-402) days and weight 5.0 (4.2-7.4) kg. Indications for MVR were insufficiency in 6 (55%), stenosis in 3 (27%), and mixed disease in 2 (18%). MEL underwent a total of 13 repairs and 4 replacements (2 mechanical, 2 bioprosthetic) prior to Melody™ valve replacement. Final valve dilation size was 18 (15.5-18.5)mm. Two (18%) children salvaged from ECMO before MEL subsequently died. Three (33%) of the 9 survivors have required subsequent MVR at 9, 17, and 23 months; 1 for severe insufficiency, and 2 for severe mixed disease. The MECH cohort was not different in age, weight, valve size, bypass or cross-clamp times, indications for replacement, or number of prior repairs or replacements (p>0.10). At 1 and 3 years, transplant free survival (MEL: 80%, 80%; MECH: 82%, 64%; p=0.180) and re-intervention (MEL: 11%, 39%; MECH: 0%, 20% p=0.32) were equivalent between groups. For children Conclusions: Melody™ MVR represents a better surgical strategy for infants less than 1 year of age requiring mitral valve replacement.

Background —Acute right ventricular (RV) restrictive physiology after tetralogy of Fallot repair results in low cardiac output and a prolonged stay in the intensive care unit (ICU). However, its mechanism remains uncertain. Methods and Results —In the first 24 hours after tetralogy of Fallot repair (n=11 patients), serial prospective measurements were performed of cardiac troponin T, indexes of NO production (NO 2 − and NO 3 − combined as NOx), and iron metabolism and antioxidants. RV diastolic function was assessed by transthoracic Doppler echocardiography. Patients who had a long stay in the ICU were characterized by restrictive RV physiology (nonrestrictive group [n=7]: 3.0±0.6 days [mean±SD]; restrictive group [n=4]: 10.7±3.1 days). Troponin T peak concentration and the area under its concentration-time curve (AUC) were higher in the restrictive RV group (peak: restrictive group 17.0±2.8 μg/L, nonrestrictive group 10.4±4.6 μg/L, P −1 · L −1 , nonrestrictive group 136.2±48.3 μg · h −1 · L −1 , P P =0.04) but were similar by 24 hours. Iron loading peaked 2 to 10 hours after bypass and was more severe in the restrictive group (peak transferrin saturation: restrictive group 83.9±13.0%, nonrestrictive group 58.3±16.2%, P =0.05; minimum total iron-binding capacity: restrictive group 0.59±0.21%, nonrestrictive group 0.76±0.06%, P =0.04; minimum iron-binding antioxidant activity to oxyorganic radicals: restrictive group 9.5±22.4%, nonrestrictive group 50.6±11.4%, P =0.01). Conclusions —After tetralogy of Fallot repair, acute restrictive RV physiology is associated with greater intraoperative myocardial injury and postoperative oxidative stress with severe iron loading of transferrin.

Background— Hybrid and Norwood strategies differ substantially in terms of stage II palliative procedures. We sought to compare these strategies with an emphasis on survival and reintervention after stage II and subsequent Fontan completion. Methods and Results— Of 110 neonates with functionally single-ventricle physiology who underwent stage I palliation between 2004 and 2010, 75 (69%) infants (Norwood, n=43; hybrid, n=32) who subsequently underwent stage II palliation were studied. Survival and reintervention rates after stage II palliation, anatomic and physiologic variables at pre-Fontan assessment, and Fontan outcomes were compared between the groups. Predictors for reintervention were analyzed. Freedom from death/transplant after stage II palliation was equivalent between the groups (Norwood, 80.4% versus hybrid, 85.6% at 3 years, P =0.66). Hybrid patients had a higher pulmonary artery (PA) reintervention rate ( P =0.003) and lower Nakata index at pre-Fontan evaluation ( P =0.015). Aortic arch and atrioventricular valve reinterventions were not different between the groups. Ventricular end-diastolic pressure, mean PA pressure, and ventricular function were equivalent at pre-Fontan assessment. There were no deaths after Fontan completion in either group (Norwood, n=25, hybrid, n=14). Conclusions— Survival after stage II palliation and subsequent Fontan completion is equivalent between the groups. The hybrid group had a higher PA reintervention rate and smaller PA size. Both strategies achieved adequate physiology for Fontan completion. Evolution of the hybrid strategy requires refinement to provide optimal PA growth.

Background— Maintaining arterial duct patency by stent implantation may be advantageous in congenital heart disease management algorithms. Rapamycin, an immunosuppressant drug that demonstrates antiproliferative properties and inhibits smooth muscle cell migration, may deter the intimal hyperplasia that occurs during spontaneous closure and after-stent implantation of the arterial duct. Methods and Results— Twenty-eight Yorkshire piglets (7 to 11 days old; weight, 2.2 to 4.9 kg) underwent stent implantation of the arterial duct (rapamycin-eluting (n=14) or bare metal (n=14) stents, 3.5-mm diameter) and were euthanized at 2, 4, and 6 weeks. Dissected arterial ducts were analyzed for lumen diameter, smooth muscle cell, and extracellular matrix components. Isolated arterial duct–derived smooth muscle cells were cultured in the presence or absence of rapamycin. Cellular proliferation rates were assessed by Ki-67 detection and [ 3 H]-thymidine incorporation. No significant neointimal proliferation was present in either stent type at 2 weeks. At 4 weeks, the median luminal diameters of the bare metal stents were 87% ( P =0.009), 54% ( P =0.004), and 77% ( P =0.004) that of the drug-eluting stents at the middle and aortic and pulmonary artery ends, respectively. At 6 weeks, the median luminal diameters of the bare metal stents were 0% ( P =0.18), 5% ( P =0.25), and 61% ( P =0.13) that of the drug-eluting stents at the same respective levels. Complete histological occlusion was found in at least 1 level of the lumen in 9 pigs: 1 (17%) in the BMS group at 4 weeks, 5 (83%) in the BMS group at 6 weeks, and 3 (50%) in the DES group at 6 weeks. In vitro studies demonstrated 50%-lower proliferation rates in rapamycin-treated cultures of duct-derived smooth muscle cell cultures ( P Conclusions— Rapamycin has antiproliferative actions on the arterial duct. Drug-eluting stents may be a more efficient tool than current palliative options for maintaining patency in critically duct-dependent states, but there may be a finite time-related benefit.

Background: Symptomatic infants with tetralogy of Fallot (TOF) and hypoplastic pulmonary arteries have higher risk for primary surgical repair. In our institution, palliation with only balloon angioplasty of the right ventricular outflow tract (RVOT) and pulmonary valve has been inconsistent and short-lived. Objectives: To evaluate our experience with percutaneous transcatheter stent implantation in the RVOT in symptomatic TOF patients. Methods: Retrospective review at the Hospital for Sick Children in Toronto, Canada from 1994 until 2007 (Group I). Outcomes were compared with our institutional primary surgical repair patients (n = 44, Group II). Results: Ten stent procedures performed in 8 patients. Median age at first intervention was 22 days (range, 3 to 119). Median weight was 3.2 kg (2.1 to 4.1). Indication for intervention was desaturation below 70% or prostaglandin dependency. Two patients required a second stenting procedure for progressive RVOT obstruction at 67 and 122 days of life. There were no major procedural complications. Discharge post stent implantation occurred at a median of 4 days (1 to 12). Median number of days from initial stent implantation to next intervention was 108 days (44 to 315). Left and right pulmonary artery diameter Z-score increased from a median of −4.3 and −3.5 to −0.9 and −0.8 respectively before surgery. For Group I and II respectively, surgical data were: repair at median age of 142 days (44 to 413) compared to 24 days (5 to 112) (P Conclusion: Stenting of the RVOT in TOF patients safely and effectively palliated symptomatic patients. This promoted development of more favourable pre-operative conditions and translated to excellent surgical outcomes. This approach represents a powerful adjunct to the management armamentarium for this challenging patient population.

Background Pulmonary regurgitation (PR) is an important determinant of outcome after repair of tetralogy of Fallot. Baseline PR was measured by magnetic resonance (MR) phase velocity mapping and from real-time right ventricular pressure-volume loops with a conductance catheter. Subsequently, the impact of two loading maneuvers (increased airway pressure, simulated branch pulmonary artery stenosis) on PR was assessed by the conductance catheter method. Methods and Results Thirteen patients, 3 to 35 years after tetralogy of Fallot repair or pulmonary valvotomy, had PR measured by MR phase velocity mapping while breathing spontaneously. During catheterization under general anesthesia, PR was estimated from right ventricular pressure-volume loops generated by conductance and microtip pressure catheters. The effect of increased airway pressure (continuous positive airway pressure, 20 cm H 2 O; n=12) and simulated branch pulmonary artery stenosis (transient balloon occlusion of a branch pulmonary artery, n=7) was measured. Basal PR fraction derived by MR and from right ventricular pressure-volume loops had a correlation coefficient of .76 and mean of differences of 2.0±18.2% (95% limits of agreement). Increased airway pressure increased PR (16.3±11.4% to 25.7±17.3%, P P P Conclusions There was reasonable agreement between MR phase velocity–derived PR fraction and that obtained from right ventricular pressure-volume loops generated by use of conductance and pressure-microtip catheters. Exacerbation of PR by increased airway pressure and branch pulmonary stenosis may be relevant to the acute postoperative and long-term management, respectively, of patients after repair of tetralogy of Fallot.