Stent Strut Dilation in Branch Pulmonary Artery Stenosis Following Stenting of Arterial Duct in Duct-dependent Pulmonary Circulation.

To assess the feasibility and outcome of stent strut dilation after arterial duct stenting with associated branch pulmonary artery (BPA) stenosis. Stenting of arterial duct in infants with duct-dependent pulmonary circulation is technically challenging. The presence of BPA stenosis is a relative contraindication for stent implantation. Infants with duct-dependent pulmonary circulation and associated BPA stenosis were assessed either by transthoracic echocardiogram alone or additional computerized tomography angiogram when required. Following ductal stenting, the stent struts of the stenosed BPA were crossed with an additional 0.014″ coronary guide wire and dilated using coronary balloons (2.0 or 2.5 mm in diameter). Seventeen (12 male) patients were considered for the procedure. The median age and weight were 27 days (range 2-94) and 2.6 kg (range 2.2-5), respectively. Fourteen patients (82.4%) underwent stent strut dilation after arterial duct stenting. Struts to left pulmonary artery was opened in 9 (64.3%) and right pulmonary artery in 5 (35.7%). The mean systemic oxygen saturation increased from 66.23 ± 8.9% at baseline to 86 ± 2.2% immediately after the stent deployment and final saturations after stent strut dilation were 89.29 ± 4.3%. Angiographic pulmonary flow improved in all cases. Stent strut dilation could not be done in 3 patients due to unfavorable anatomy. One patient had acute stent thrombosis and died in the hospital. Two others died during follow-up, during an acute febrile illness and gastroenteritis. All survivors underwent cardiac surgery and were on regular follow-up. Strut dilation of BPA stenosis is feasible to augment pulmonary blood flow, following arterial duct stenting. This procedure may be useful in selected patients with BPA stenosis to have uniform growth of pulmonary arteries.

Patterns of Electrocardiographic Abnormalities in Children with Hypertrophic Cardiomyopathy.

Hypertrophic cardiomyopathy (HCM), a common cardiomyopathy in children, is an important cause of morbidity and mortality. Early recognition and appropriate management are important. An electrocardiogram (ECG) is often used as a screening tool in children to detect heart disease. The ECG patterns in children with HCM are not well described.ECGs collected from an international cohort of children, and adolescents (≤ 21 years) with HCM were reviewed. 482 ECGs met inclusion criteria. Age ranged from 1 day to 21 years, median 13 years. Of the 482 ECGs, 57 (12%) were normal. The most common abnormalities noted were left ventricular hypertrophy (LVH) in 108/482 (22%) and biventricular hypertrophy (BVH) in 116/482 (24%) Of the patients with LVH/BVH (n = 224), 135 (60%) also had a strain pattern (LVH in 83, BVH in 52). Isolated strain pattern (in the absence of criteria for hypertrophy) was seen in 43/482 (9%). Isolated pathologic Q waves were seen in 71/482 (15%). Pediatric HCM, 88% have an abnormal ECG. The most common ECG abnormalities were LVH or BVH with or without strain. Strain pattern without hypertrophy and a pathologic Q wave were present in a significant proportion (24%) of patients. Thus, a significant number of children with HCM have ECG abnormalities that are not typical for "hypertrophy". The presence of the ECG abnormalities described above in a child should prompt further examination with an echocardiogram to rule out HCM.

Indications for and outcomes of interstage catheter interventions following the Norwood procedure: A single-institution study.

Aims: The aim of this study was to document the incidence, types, and outcome of interstage catheter interventions following the Norwood surgical palliation. Patients and Methods: A retrospective single-center study of all patients surviving the Norwood operation was performed. All data concerning interstage catheter interventions up to the completion of the superior cavopulmonary shunt were collected. Results: Catheter interventions were performed in 62 of 94 patients (66%; 38 males). These included interventions on the aortic arch (n = 44), the branch pulmonary arteries (PAs) (n = 17), and the Sano shunt (n = 14). Multiple interventions and repeat interventions were common. The minimum aortic arch diameter (pre- versus posttreatment) increased from median 3.1 (2.3-3.3) mm to 5.1 (4.2-6.2) mm (P < 0.001). The catheter pullback gradient decreased from 40 (36-46) mmHg to 9 (5-10) mmHg (P < 0.001), and the echocardiographic gradient from 54 (45-64) mmHg to 12 (10-16) mmHg (P < 0.001). The branch PA diameters increased from 2.4 (2.1-3.0) mmHg to 4.7 (4.2-5.1) mmHg (P < 0.001). The minimum Sano shunt diameters increased from 2.0 (1.5-2.1) mm to 5.9 (5.8-6.0) mm (P < 0.001); this was associated with an improvement in systemic saturation from 63% (60%-65%) to 80% (79-82%) (P < 0.001). Unexpected interstage death at home occurred in two patients who had received no interventions. The remainder received a superior cavopulmonary shunt palliation. Conclusions: Catheter interventions were common. Systematic follow-up and a low threshold for reintervention are essential to the success of staged surgical palliation for this patient cohort.

Initial Clinical Trial of a Novel Pulmonary Valved Conduit.

Valved allografts and xenografts for reconstruction of the right ventricular outflow tract (RVOT) lack durability and do not grow. We report the first clinical use of a completely bioabsorbable valved conduit (Xeltis pulmonary valve - XPV) in children. Twelve children (six male), median age five (two to twelve) years and median weight 17 (10 to 43) kg, underwent RVOT reconstruction with the XPV. Diagnoses were: pulmonary atresia with ventricular septal defect (VSD) (n = 4), tetralogy of Fallot (n = 4), common arterial trunk (n = 3), and transposition of the great arteries with VSD and pulmonary stenosis (n = 1). All had had previous surgery, including prior RVOT conduit implantation in six. Two diameters of conduit 16mm (n = 5) and 18mm (n = 7) were used. At 24 months none of the patients has required surgical re-intervention, 9 of the 12 are in NYHA functional class I and three patients in NYHA class II. None of the conduits has shown evidence of progressive stenosis, dilation or aneurysm formation. Residual peak gradient of >40 mm Hg was observed in three patients, caused by kinking of the conduit at implantation in 1 and distal stenosis in the peripheral pulmonary arteries in 2 patients. Five patients developed severe pulmonary valve insufficiency (PI); the most common mechanism was prolapse of at least one of the valve leaflets. The XPV conduit is a promising innovation for RVOT reconstruction. Progressive PI requires however an improved design (geometry, thickness) of the valve leaflets.

Interventional recanalisation of long segment aortic atresia.

We report the case of a long-segment aortic atresia as the cause for therapy resistant arterial hypertension in a young adult. Recanalization was achieved interventionally by wire-crossing and stent implantation with subsequent normalization of blood pressure.

Emerging clinical applications of strain imaging and three-dimensional echocardiography for the assessment of ventricular function in adult congenital heart disease.

Management of congenital heart disease (CHD) in adults (ACHD) remains an ongoing challenge due to the presence of residual hemodynamic lesions and development of ventricular dysfunction in a large number of patients. Echocardiographic imaging plays a central role in clinical decision-making and selection of patients who will benefit most from catheter interventions or cardiac surgery.. Recent advances in both strain imaging and three-dimensional (3D)-echocardiography have significantly contributed to a greater understanding of the complex pathophysiological mechanisms involved in CHD. The aim of this paper is to provide an overview of emerging clinical applications of speckle-tracking imaging and 3D-echocardiography in ACHD with focus on functional assessment, ventriculo-ventricular interdependency, mechanisms of electromechanical delay, and twist abnormalities in adults with tetralogy of Fallot (TOF), a systemic RV after atrial switch repair or in double discordance ventricles, and in those with a Fontan circulation.

Subclinical myocardial disease in patients with primary hyperoxaluria and preserved left ventricular ejection fraction: a two-dimensional speckle-tracking imaging study.

BACKGROUND: Primary hyperoxaluria (PH) is characterized by progressive chronic kidney disease (CKD) and systemic oxalate deposition. Myocardial dysfunction might be present early in the course of the disease. However, this hypothesis has not yet been tested in the PH population. Therefore, we aimed to determine whether strain imaging using two-dimensional speckle tracking echocardiography (2D-STE) might detect subclinical myocardial disease in otherwise asymptomatic PH patients. METHODS: Prospective study of pediatric and adolescent PH patients with preserved LV ejection fraction (LV EF) and without renal replacement therapy. Subjects underwent conventional echocardiography and 2D-STE. Global (GLS) and segmental peak systolic LV longitudinal strain (LS) measurements were obtained. Data were compared with age- and gender-matched controls, and Z-scores were calculated as appropriate. RESULTS: Fifteen PH patients (age 14.1 ± 5.9 years; 13/15 in CKD stages 1-2) were studied. Although LV EF was preserved (63 ± 6%) in patients, GLS was significantly impaired (GLS - 17.1 ± 2.2% vs - 22.4 ± 1.9%, p < 0.001). This was mainly due to decreased LS values in the apical segments (p < 0.05). Echocardiographic indices of ventricular wall thickness were significantly increased in patients compared to controls (all p < 0.03). GLS correlated significantly with Z-scores of diastolic interventricular wall thickness (r = - 0.57, p = 0.025) and moderately with serum creatinine levels (r = 0.53, p = 0.044). No correlation was found between GLS and blood pressure measurements. CONCLUSIONS: Subclinical myocardial disease is already present early in the course of disease in PH patients with preserved LV EF and some degree of renal dysfunction, but without overt systemic oxalosis. Current recommendations to screen only PH patients with advanced CKD for cardiac disease should be revised accordingly.

Impact of Obesity on Left Ventricular Thickness in Children with Hypertrophic Cardiomyopathy.

Obesity is associated with additional left ventricular hypertrophy (LVH) in adults with hypertrophic cardiomyopathy (HCM). It is not known whether obesity can lead to further LVH in children with HCM. Echocardiographic LV dimensions were determined in 504 children with HCM. Measurements of interventricular septal thickness (IVST) and posterior wall thickness (PWT), and patients' weight and height were recorded. Obesity was defined as a body mass index (BMI) ≥ 99th percentile for age and sex. IVST data was available for 498 and PWT data for 484 patients. Patient age ranged from 2 to 20 years (mean ± SD, 12.5 ± 3.9) and 340 (68%) were males. Overall, patient BMI ranged from 7 to 50 (22.7 ± 6.1). Obesity (BMI 18-50, mean 29.1) was present in 140 children aged 2-19.6 (11.3 ± 4.1). The overall mean IVST was 20.5 ± 9.6 mm and the overall mean PWT was 11.0 ± 8.4 mm. The mean IVST in the obese patients was 21.6 ± 10.0 mm and mean PWT was 13.3 ± 14.7 mm. The mean IVST in the non-obese patients was 20.1 ± 9.5 mm and mean PWT was 10.4 ± 4.3 mm. Obesity was not significantly associated with IVST (p = 0.12), but was associated with increased PWT (0.0011). Obesity is associated with increased PWT but not IVST in children with HCM. Whether obesity and its impact on LVH influences clinical outcomes in children with HCM needs to be studied.

Successful biventricular cardiac resynchronization therapy in a failing Fontan patient: Implications of ventriculo-ventricular interdependency in single ventricle physiology.

We describe a Fontan patient with severe heart failure who was successfully treated with biventricular cardiac resynchronization therapy (CRT). Our case shows that strain imaging might play a crucial role in guiding placement of pacing leads and in characterizing the electromechanical substrate associated with a favorable CRT response. Furthermore, we demonstrate for the first time that ventriculo-ventricular interdependency seems an important mechanical concept, which can be utilized to augment cardiac performance in failing Fontan patients with a functional hypoplastic ventricle.

Risk factors for lethal arrhythmic events in children and adolescents with hypertrophic cardiomyopathy and an implantable defibrillator: An international multicenter study.

BACKGROUND: Predictors of risk of lethal arrhythmic events (LAE) is poorly understood and may differ from adults in children with hypertrophic cardiomyopathy (HCM). OBJECTIVE: The purpose of this study was to determine predictors of LAE in children with HCM. METHODS: A retrospective data collection was performed on 446 children and teenagers 20 years and younger (290 [65%] male; mean age 10.1 ± 5.7 years) with idiopathic HCM from 35 centers. Patients were classified as group 1 (HCM with LAE) if having a secondary prevention implantable cardioverter-defibrillator (ICD) or primary prevention ICD with appropriate interventions or group 2 (HCM without LAE) if having a primary prevention ICD without appropriate interventions. RESULTS: There were 152 children (34%) in group 1 and 294 (66%) in group 2. Risk factors for group 1 by univariate analysis were septal thickness, posterior left ventricular (LV) wall thickness, lower LV outflow gradient, and Q wave > 3 mm in inferior electrocardiographic leads. Factors not associated with LAE were family history of SCD, abnormal blood pressure response to exercise, and ventricular tachycardia on ambulatory electrocardiographic monitoring. Risk factors for SCD by multivariate analysis were age at ICD placement (hazard ratio [HR] 0.9; P = .0025), LV posterior wall thickness z score (HR 1.02; P < .005), and LV outflow gradient < 30 mm Hg (HR 2.0; P < .006). LV posterior wall thickness z score ≥ 5 was associated with LAE. CONCLUSION: Risk factors for LAE appear different in children compared to adults. Conventional adult risk factors were not significant in children. Further prospective studies are needed to improve risk stratification for LAE in children with HCM.

Off-label use of duct occluder devices to close hemodynamically significant perimembranous ventricular septal defects: A multicenter experience.

OBJECTIVE: We sought to evaluate the feasibility, technical aspects, and outcome of transcatheter perimembranous ventricular septal defect (pmVSD) closure using duct occluder devices with a single retention disc. BACKGROUND: Use of duct occluder devices to close pmVSD seems a promising alternative therapy. However, limited data exist on this technique. METHODS: From 2010 to 2016, 222 patients (female 47.7%) were identified from databases of five participating institutions in whom pmVSD closure was attempted using an Amplatzer Duct Occluder I or Lifetech duct occluder device. RESULTS: Patients ranged in age from 0.7 to 52 years (median, 7.0 years) and in weight from 4.0 to 70 kg (median, 18.0 kg). The mean size of the VSD was 6.8 ± 2.2 mm. A large defect (> 6 mm) was present in 137 patients (61.7%). Device closure was successful in 218 patients (98.2%). The 10/8 mm device was used in most patients (n = 85, 38.3%), and the vascular approach was from the femoral vein in 169 patients (76.1%). There were 18 early complications in 17/218 patients (7.8%). Three patients (1.4%) developed complete heart block (transient n = 2; requiring permanent pacing n = 1). Median follow-up was 6 months (6 months-6 years). A mild residual shunt was seen in 10 patients at 6 months follow-up. CONCLUSIONS: The immediate results of transcatheter pmVSD closure using a duct occluder device with a single retention disc are promising. It is an effective technique with a lower rate of complications than for other currently available devices.

Catheter Ablation of Ventricular Arrhythmia for Ebstein's Anomaly in Unoperated and Post-Surgical Patients.

OBJECTIVES: The purpose of this study was to determine the ventricular arrhythmia (VA) substrates in patients with unoperated and post-surgical Ebstein's Anomaly (EA). BACKGROUND: EA is associated with variable atrialization of the right ventricle and a propensity for VA and sudden death. There are scant data on catheter ablation for VA in this population. METHODS: This was a retrospective study involving 11 congenital heart disease centers. RESULTS: A total of 24 patients (median age 17 [interquartile range (IQR): 11 to 37] years; age range 1 to 68 years; 42% men) with EA undergoing catheter ablation were identified. Prior tricuspid valve (TV) surgery had been performed in 12 (50%). Presenting symptoms were palpitations in 15, syncope in 4, aborted cardiac arrest in 4, and none in 1. At procedure, 28 VA substrates were encountered and 25 were completely characterized (median 1 per patient; cycle length 305 [IQR: 268 to 400] ms). In 3 cases, premature ventricular contraction (PVC) foci were targeted (1 with a history of PVC-induced ventricular fibrillation). VA mechanisms were focal in 15 and macro-re-entrant in 10, and did not differ significantly between those with and those without prior TV surgery (p = 0.7). Focal VAs predominantly localized to the atrialized right ventricle ARV in unoperated patients and to diseased myocardium or Purkinje tissue after TV surgery. Macro-re-entry was related to isolated scar or split potentials in the ARV in unoperated patients, and larger, more diffuse scar after TV surgery. Complete success was achieved in 22 (92%). There were 2 of 13 complications in patients <18 years of age and none in patients >18 years of age. There was a single recurrence over a median follow-up of 3.4 years. CONCLUSIONS: VA in EA may be either focal or macro-re-entrant. In the absence of surgery, substrates chiefly involve the ARV. After surgery, focal VA involves injured myocardium or Purkinje tissue and re-entrant ventricular tachycardia is related to post-surgical scar. Catheter ablation is a reasonable therapeutic approach for these patients.

Predictors of electrocardiographic screening failure for the subcutaneous implantable cardioverter-defibrillator in children: A prospective multicenter study.

BACKGROUND: Subcutaneous implantable cardioverter-defibrillator (SICD) shows promise for select patients at risk of sudden cardiac death. However, patients need to pass an electrocardiographic (ECG) screening (ECG-S) test before they can receive an SICD. Predictors of ECG-S failure in children are unclear. OBJECTIVE: The purpose of this study was to identify the incidence and predictive factors for failure of ECG-S in children. METHODS: Patients 18 years and younger with a preexisting ICD underwent ECG-S for SICD. ECG and demographic data were analyzed for factors predictive of failure. RESULTS: Seventy-three patients (mean age 14.2 ± 3.3 years; range 5-18 years) with hypertrophic cardiomyopathy (n = 24, 33%), long QT syndrome (n =18, 25%), other inherited arrhythmia syndromes (n = 20, 27%), congenital heart disease (n = 9, 12%), and miscellaneous conditions (n = 2) with an existing transvenous ICD underwent prospective ECG-S. Nineteen (26%) failed ECG-S. Failed patients had a longer corrected QT (QTc) interval (457 ms vs 425 ms; P = .03), a longer QRS duration (120 ms vs 98 ms; P = .04), and a lower ratio of R-wave to T-wave amplitudes (R:T ratio) in lead aVF (4 vs 5; P = .001). Multivariable logistic regression identified QTc interval (odds ratio [OR] 4.31; P = .04), QRS duration (OR 4.93; P = .03), R:T ratio in lead aVF (OR 3.13; P = .08) as predictors of failure. A risk score with 1 point each for QTc interval >440 ms, QRS duration >120 ms, and R:T ratio <6.5 in lead aVF was associated with probability of failure of 15.4% (1 point), 47.4% (2 points), and 88.6% (3 points), respectively. CONCLUSION: ECG-S failure for SICD occurred in 26% of children, which is higher than the reported incidence in adults. Factors predicting ECG-S failure included longer QTc interval, longer QRS duration, and lower R:T ratio in lead aVF.

Implantation of a subcutaneous implantable cardioverter defibrillator with right parasternal electrode position in a patient with D-transposition of the great arteries and concomitant AAI pacemaker: a case report.

BACKGROUND: Implantable cardioverter defibrillator (ICD) therapy is indicated in patients with structural heart disease who have had an aborted cardiac arrest (ACA). After atrial repair of d-transposition of the great arteries (d-TGA, Mustard repair) patients seem to be at a higher risk of failing intraoperative subcutaneous ICD (S-ICD) shock testing. CASE SUMMARY: We report the case of a 45-year-old patient with congenital heart disease (CHD) who suffered a cardiac arrest from ventricular fibrillation and was subsequently implanted with a S-ICD. We describe the challenges of ICD therapy in patients after Mustard procedure for d-TGA, with the additional challenge of concomitant AAI pacemaker therapy. In this patient, we opted for the implantation of an S-ICD, and detail the necessary considerations and operative technique employed in this patient. A right parasternal electrode position was chosen and intraoperative shock testing was successful. DISCUSSION: Patients after atrial switch surgery for d-TGA and ACA require careful consideration of the appropriate type of ICD therapy. Subcutaneous ICD implantation with right parasternal electrode position may be a viable option in these patients.

The development of pacing induced ventricular dysfunction is influenced by the underlying structural heart defect in children with congenital heart disease.

BACKGROUND: Right ventricular pacing can cause pacing-induced ventricular dysfunction (PIVD) correctable with biventricular pacing (BiVP). Factors associated with PIVD are poorly understood. METHODS: We reviewed children receiving epicardial dual-chamber pacemakers for complete heart block (CHB) after congenital heart disease (CHD) surgery. PIVD was defined as% fractional shortening <15% improving after BiVP. RESULTS: Between 2005 and 2014, 47 children <2years developed CHB after CHD surgery. All had biventricular hearts and underwent epicardial dual chamber pacemaker implantation. Nine of the 47 (19%) developed PIVD. PIVD occurred in 0/10 with ventricular septal defect (VSD), 0/6 with tetralogy of Fallot, 2/6 with double outlet right ventricle, 2/6 with transposition and VSD, 3/9 with atrioventricular canal defect, 1/2 with mitral valve replacement; 1/3 with congenitally corrected TGA repair; and 0/3 with atrioventricular canal plus tetralogy of Fallot and 0/1 with subaortic membrane. QRS duration (QRSD) was 84-170 (median 135ms) in the non PIVD group and 100-168 (median 124) ms in the PIVD group. Percentage fractional shortening (%FS) while paced was 16-46, median 30% in the non-PIVD group and 6-15 (median 11%) in the PIVD group.%FS post upgrade to BiVP (with an epicardial LV lead) in the 9 patients with PIVD was 23-33 (median 29%). CONCLUSIONS: PIVD occurred in certain CHD but not others. Prolonged QRSD was not associated with PIVD. The predilection for RV pacing to result in PIVD in certain types of CHD needs further study.

Stenting the Fontan pathway in paediatric patients with obstructed extracardiac conduits.

OBJECTIVES: An unobstructed extracardiac conduit (ECC) is essential for optimal Fontan haemodynamics. We aimed to evaluate the feasibility and results of percutaneous transcatheter stenting of the ECC in paediatric patients with a significant Fontan pathway obstruction. METHODS: Our institutional database was searched to identify all Fontan patients who had a stent placed in their ECC. Medical records, cardiac catheterisation data and echocardiographic investigations were reviewed. Vessel diameters were normalised to account for differences in body surface area. RESULTS: Nineteen Fontan patients (age 6.5±3.2 years; male 78.9%) with a significant stenosis of their Dacron ECC graft were identified. Seven patients presented with protein-losing enteropathy (36.8%). An ECC obstruction was suspected on echocardiography in only 6/19 patients (31.6%). The mean minimum diameter of the ECC was 8.3±2.4 mm. A stenosis of >45% was seen in the majority of patients (n=12, 63.1%). Significant correlations between the severity of the ECC obstruction and Fontan pathway vessel diameters were found (all p<0.05). Stenting was successful in all children. The ECC diameter increased significantly after stenting (p<0.0001). An acute clinical benefit of ECC stenting was observed in 18/19 (94.7%) patients. ECC patency was good during a mean follow-up of 1.8±0.9 years. CONCLUSIONS: The feasibility and acute results of percutaneous transcatheter ECC stenting are promising and may provide a good alternative to postpone surgery to a later age. The mechanisms contributing to the development of ECC stenoses are likely multifactorial.

The electrocardiogram of the neonate and infant.

The ECG in children has a number of characteristic differences compared to the ECG of the adult. The transition of the ECG in neonates after birth represents dynamic changes of the circulatory system due to the postnatal adaptation, different physiologic properties of the fetal and neonatal myocardium, the location and orientation of the heart in the chest and influence of body mass during that period and later on in childhood. The complexity of the changes implies a broad variation of ECG changes during the first days and weeks of life, whose interpretation requires expert knowledge. The ECG is an obligatory diagnostic tool in childhood arrhythmias. The long QT syndrome is an inherited rhythm disorder with risk of sudden cardiac death in early childhood. Electrocardiographic screening in neonates for the early detection of LQTS might identify individuals with an abnormal repolarization and prevent sudden death. The potential benefits of a universal screening program, even if achievable logistically and in a cost-effective manner, are however highly debatable.

Postnatal Development of Right Ventricular Myofibrillar Biomechanics in Relation to the Sarcomeric Protein Phenotype in Pediatric Patients with Conotruncal Heart Defects.

BACKGROUND: The postnatal development of myofibrillar mechanics, a major determinant of heart function, is unknown in pediatric patients with tetralogy of Fallot and related structural heart defects. We therefore determined the mechanical properties of myofibrils isolated from right ventricular tissue samples from such patients in relation to the developmental changes of the isoforms expression pattern of key sarcomere proteins involved in the contractile process. METHODS AND RESULTS: Tissue samples from the infundibulum obtained during surgery from 25 patients (age range 15 days to 11 years, median 7 months) were split into half for mechanical investigations and expression analysis of titin, myosin heavy and light chain 1, troponin-T, and troponin-I. Of these proteins, fetal isoforms of only myosin light chain 1 (ALC-1) and troponin-I (ssTnI) were highly expressed in neonates, amounting to, respectively, 40% and 80%, while the other proteins had switched to the adult isoforms before or around birth. ALC-1 and ssTnI expression subsequently declined monoexponentially with a halftime of 4.3 and 5.8 months, respectively. Coincident with the expression of ssTnI, Ca(2+) sensitivity of contraction was high in neonates and subsequently declined in parallel with the decline in ssTnI expression. Passive tension positively correlated with Ca(2+) sensitivity but not with titin expression. Contraction kinetics, maximal Ca(2+)-activated force, and the fast phase of the biphasic relaxation positively correlated with the expression of ALC-1. CONCLUSIONS: The developmental changes in myofibrillar biomechanics can be ascribed to fetal-to-adult isoform transition of key sarcomeric proteins, which evolves regardless of the specific congenital cardiac malformations in our pediatric patients.