Challenges of interpreting copy number variation in syndromic and non-syndromic congenital heart defects.

Array comparative genomic hybridization (aCGH) has led to an increased detection of causal chromosomal imbalances in individuals with congenital heart defects (CHD). The introduction of aCGH as a diagnostic tool in a clinical cardiogenetic setting entails numerous challenges. Based on our own experience as well as those of others described in the literature, we outline the state of the art and attempt to answer a number of outstanding questions such as the detection frequency of causal imbalances in different patient populations, the added value of higher-resolution arrays, and the existence of predictive factors in syndromic cases. We introduce a step-by-step approach for clinical interpretation of copy number variants (CNV) detected in CHD, which is primarily based on gene content and overlap with known chromosomal syndromes, rather than on CNV inheritance and size. Based on this algorithm, we have reclassified the detected aberrations in aCGH studies for their causality for syndromic and non-syndromic CHD. From this literature overview, supplemented with own investigations in a cohort of 46 sporadic patients with severe non-syndromic CHD, it seems clear that the frequency of causal CNVs in non-syndromic CHD populations is lower than that in syndromic CNV populations (3.6 vs. 19%). Moreover, causal CNVs in non-syndromic CHD mostly involve imbalances with a moderate effect size and reduced penetrance, whereas the majority of causal imbalances in syndromic CHD consistently affects human development and significantly reduces reproductive fitness.

Infective endocarditis in patients after percutaneous pulmonary valve implantation with the stent-mounted bovine jugular vein valve: Clinical experience and evaluation of the modified Duke criteria.

AIMS: Percutaneous pulmonary valve implantation (PPVI) has proven good hemodynamic results. As infective endocarditis (IE) remains a potential complication with limited available clinical data, we reviewed our patient records to improve future strategies of IE prevention, diagnosis and treatment. METHODS: Medical records of all patients diagnosed with Melody® valve IE according to the modified Duke criteria were retrospectively analyzed in three Belgian tertiary centers. RESULTS: 23 IE episodes in 22 out of 240 patients were identified (incidence 2.4% / patient year) with a clear male predominance (86%). Median age at IE was 17.9 years (range 8.2-45.9 years) and median time from PPVI to IE was 2.4 years (range 0.7-8 years). Streptococcal species caused 10 infections (43%), followed by Staphylococcus aureus (n = 5, 22%). In 13/23 IE episodes a possible entry-point was identified (57%). IE was classified as definite in 15 (65%) and as possible in 8 (35%) cases due to limitations of imaging. Echocardiography visualized vegetations in only 10 patients. PET-CT showed positive FDG signals in 5/7 patients (71%) and intracardiac echocardiography a vegetation in 1/1 patient (100%). Eleven cases (48%) had a hemodynamically relevant pulmonary stenosis at IE presentation. Nine early and 6 late percutaneous or surgical re-interventions were performed. No IE related deaths occurred. CONCLUSIONS: IE after Melody® valve PPVI is associated with a relevant need of re-interventions. Communication to patients and physicians about risk factors is essential in prevention. The modified Duke criteria underperformed in diagnosing definite IE, but inclusion of new imaging modalities might improve diagnostic performance.

Progressive myoclonic epilepsy as an adult-onset manifestation of Leigh syndrome due to m.14487T>C.

BACKGROUND: m.14487T>C, a missense mutation (p.M63V) affecting the ND6 subunit of complex I of the mitochondrial respiratory chain, has been reported in isolated childhood cases with Leigh syndrome (LS) and progressive dystonia. Adult-onset phenotypes have not been reported. OBJECTIVES: To determine the clinical-neurological spectrum and associated mutation loads in an extended m.14487T>C family. METHODS: A genotype-phenotype correlation study of a Belgian five-generation family with 12 affected family members segregating m.14487T>C was carried out. Clinical and mutation load data were available for nine family members. Biochemical analysis of the respiratory chain was performed in three muscle biopsies. RESULTS: Heteroplasmic m.14487T>C levels (36-52% in leucocytes, 97-99% in muscle) were found in patients with progressive myoclonic epilepsy (PME) and dystonia or progressive hypokinetic-rigid syndrome. Patients with infantile LS were homoplasmic (99-100% in leucocytes, 100% in muscle). We found lower mutation loads (between 8 and 35% in blood) in adult patients with clinical features including migraine with aura, Leber hereditary optic neuropathy, sensorineural hearing loss and diabetes mellitus type 2. Despite homoplasmic mutation loads, complex I catalytic activity was only moderately decreased in muscle tissue. INTERPRETATION: m.14487T>C resulted in a broad spectrum of phenotypes in our family. Depending on the mutation load, it caused severe encephalopathies ranging from infantile LS to adult-onset PME with dystonia. This is the first report of PME as an important neurological manifestation of an isolated mitochondrial complex I defect.

Application of a postnatal prediction model of survival in CDH in the era of fetal therapy.

Background: The disease severity in patients with a congenital diaphragmatic hernia (CDH) is highly variable. To compare patient outcomes, set up clinical trials and come to severity-based treatment guidelines, a performant prediction tool early in neonatal life is needed.Objective: The primary purpose of this study was to validate the CDH study group (SG) prediction model for survival in neonates with CDH, including patients who had fetal therapy. Secondary, we aimed to assess its predictive value for early morbidity.Methods: This is a retrospective single-center study at the University Hospitals Leuven on all infants with a diagnosis of CDH live-born between April 2002 and December 2016. The prediction model of the CDHSG was applied to evaluate its performance in determining mortality risk. Besides, we examined its predictive value for early morbidity parameters, including duration of ventilation, respiratory support on day 30, time to full enteral feeding and length of hospital stay.Results: The CDHSG prediction model predicted survival well, with an area under the curve of 0.796 (CI: 0.720-0.871). It had poor value in predicting infants who needed respiratory support on day 30 (area under the curve (AUC) 0.606; CI: 0.493-0.719), and correlated poorly with duration of ventilation, time to full enteral feeding and length of hospital stay.Conclusion: The CDHSG prediction model was in our hands also a useful tool in predicting mortality in neonates with CDH in the fetal treatment era. Correlation with early morbidity was poor.RationaleObjectives: (1) Validation of the CDHSG prediction model for survival in a cohort of neonates with CDH, in whom fetal endoscopic tracheal occlusion was applied according to the severity of lung hypoplasia. (2) Evaluation of performance of the model in the prediction of early morbidity.Main results: (1) Confirmation of the predictive value of the model for survival in neonates with CDH in the era of fetal therapy. (2) No correlation of the model with early morbidity parameters.

Transapical left ventricular access for difficult to reach interventional targets in the left heart.

OBJECTIVE: Interventional targets may be virtually "excluded" due to vascular access problems or complex previous surgical procedures. This study reviews our experience using transapical ventricular puncture to gain direct access to the systemic ventricle. PATIENTS: Patient 1 (74 years, 2 previous sternotomies), patient 2 (66 years, 5 previous sternotomies), and patient 5 (69 years, 3 previous sternotomies) with prosthetic valves had paravalvular mitral valve leaks. Patient 3 (6.3 years, 2 previous sternotomies) with an extracardiac Fontan conduit, had a significant residual leak after two previous surgical attempts of patch closure of a severely regurgitant right atrioventricular valve. Patient 4 (10 months) had failure of standard ablation of the posteroseptal region of the mitral valve with persistent life-threatening episodes of ventricular tachycardia. METHODS: Procedures were performed under general anesthesia. Entry site was percutaneous in three patients and in two (and one conversion) a mini-thoracotomy was used. Sheaths were placed (6 F) using standard Seldinger technique, followed by the procedure as required. Direct surgical closure of the puncture site was done in 4 patients and in patient 3, a percutaneous vascular occlusion device was used. RESULTS: Easy and immediate access was obtained in all patients. The paravalvular leaks were crossed within seconds and completely closed with Amplatzer occluders. In patient 3 the valve was crossed using a Brokenbrough needle and a 12-mm Amplatzer device was placed in the patch leak. Patient 4 was successfully ablated using a 7-F irrigated catheter endo- and epicardially. Complications were in the percutaneous puncture group: in one patient a coronary artery was punctured and in one a hemothorax developed. CONCLUSION: Direct left ventricular puncture offers a very useful alternative access site in selected patients to reach "inaccessible" targets for certain percutaneous interventions in patients where standard approaches may be impossible or difficult.

Therapy for foetal pericardial tumours: survival following in utero shunting, and literature review.

We report the first case of foetal pericardial teratoma, treated successfully in utero by pericardio-amniotic shunting, and review the relevant literature. Foetal treatment improves survival in case of hydrops. Foetal pericardio-amniotic shunting could possibly be an alternative to serial pericardiocentesis.

Radiation dose survey in a paediatric cardiac catheterisation laboratory equipped with flat-panel detectors.

Flat-panel X-ray detectors for fluoroscopy represent a modern imaging equipment that is being implemented in paediatric cardiac catheterisation laboratories. Infants and children represent a group of patients with a high radiosensitivity. A survey of 273 (126 diagnostic and 147 therapeutic) paediatric catheterisations was performed to investigate the radiation doses delivered by the new X-ray system. Statistical parameters (75th, 50th and 25th percentiles) of dose-area product (DAP) and fluoroscopy time are reported for patients divided into six age groups: 0-30 d, >1-12 m, >1-3, >3-5, >5-10 and >10-15 y. For accurate risk estimation, effective dose (E) has been determined for all patients using the PCXMC software. For diagnostic procedures, the third quartile of E ranges from 11.3 mSv for newborns to 7 mSv for children of 10-15 y. Therapeutic procedures are more complex than diagnostic. Consequently, the third quartile of E is 22.6 mSv (0-30 d), 18.6 (>1-12 m), 13.3 (>1-3 y), 21.5 (>3-5 y), 17.8 (>5-10 y) and 34.1 mSv (>10-15 y). Dose conversion factors, which relate the DAP and E, have been estimated for each age group. The results of this study may serve as a first step in the optimisation process, in order to make full use of the dose reduction potential of flat-panel systems.

Molecular cytogenetic characterization of a constitutional complex intrachromosomal 4q rearrangement in a patient with multiple congenital anomalies.

Constitutional Complex Chromosomal Rearrangements (CCRs) are very rare. While the vast majority of CCRs involve more than one chromosome, only seven cases describe CCRs with four or more breakpoints within a single chromosome. Here, we present a patient with multiple congenital anomalies and mental retardation. Array Comparative Genomic Hybridisation (array CGH), FISH and Multicolour Banding FISH revealed a de novo complex rearrangement with two deletions, a duplication and an inversion of 4q. This CCR involving at least seven breakpoints is one of the most complex rearrangements of a single chromosome reported thus far. Potential mechanisms generating such complex rearrangements are discussed.

Rheologic genesis of discrete subvalvular aortic stenosis: a Doppler echocardiographic study.

To determine whether morphologic structures or abnormal flow patterns predispose to pathologic proliferation of subvalvular tissue, 26 patients (mean age 19.8 +/- 10.3 years) were studied greater than or equal to 6 months after operation for isolated discrete subvalvular aortic stenosis. The aortic root diameter and the mitral-aortic separation were measured with sector echocardiography. Flow patterns in the left ventricular outflow tract of these patients and control subjects were evaluated with a color flow mapping system optimized for the detection of turbulence. All control subjects had laminar flow throughout systole in the left ventricular outflow tract. By contrast, turbulence originating well below the site where the shelf had previously been resected was observed in 20 (77%) of the 26 patients. In 16 of these 20 patients turbulence was caused by a ridge, which in 13 patients could be identified as the offshoot of a ventricular band. In four patients the turbulence was caused by malalignment of the muscular and membranous septum, resulting in protrusion of the muscular septum into the outflow tract. Except for the latter four patients, the aortic root diameter was 84 +/- 10% of values predicted by body surface area, with values in six patients falling below the third percentile (p less than 0.01). The mitral-aortic separation was 9.7 +/- 3.5 mm, values in 21 patients falling above the 97th percentile (p less than 0.001). These data support the theory that discrete subvalvular aortic stenosis may be caused by a chronic flow disturbance, preferably in a small and long outflow tract. Left ventricular bands, if reaching the outflow tract, may be a factor.(ABSTRACT TRUNCATED AT 250 WORDS)

ALCAPA syndrome: an example of chronic myocardial hypoperfusion?

OBJECTIVES: The purpose of this study was to evaluate functional variables and morphologic correlates of chronically hypoperfused myocardium before and after revascularization. BACKGROUND: Neonates with congenital anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA syndrome) develop some myocardial necrosis shortly after birth. The survivors of this event are left with a localized infarction and an almost entirely collateral circulation-dependent perfusion of the left ventricle that results in poor global left ventricular function. Survival beyond infancy is uncommon because of severe left heart failure. Revascularization, however, brings about functional recovery with good clinical outcome. The ALCAPA syndrome is thus characterized by chronic collateral circulation-dependent low perfusion, low contraction matching and potential revivability. METHODS: Five patients with ALCAPA syndrome are presented, with preoperative and postoperative clinical findings and histologic data obtained from intraoperative transmural biopsy specimens. RESULTS: The angiographically assessed preoperative ejection fraction was 33 +/- 19% (mean +/- SD). Postoperative echocardiographic follow-up revealed normal left ventricular function in all patients. Histologic study of the biopsy specimens taken from the region perfused by the anomalous artery showed a variable degree of fibrosis (51 +/- 32%). The ultrastructure of the remaining myocytes revealed viable characteristics, but a substantial percent (46 +/- 26%) showed a markedly reduced fraction of contractile material. CONCLUSIONS: These ultrastructural studies suggest delayed subcellular adaptive responses in the chronically hypoperfused myocardium of patients with ALCAPA syndrome.

Exercise responses in patients with congenital heart disease after Fontan repair: patterns and determinants of performance.

After a Fontan repair for congenital heart disease, 42 patients underwent graded supine bicycle exercise tests at levels relevant to normal daily activities. Results were compared with those of 28 age-matched normal control subjects. At rest, the cardiac index, stroke index and systolic blood pressure were comparable in both groups, but increases with exercise were smaller in the patients with a Fontan circulation. The heart rate at rest was higher in the Fontan group, but this difference disappeared as soon as exercise started. To determine whether there are limitations intrinsic to the Fontan circulation at these levels of exercise, the 10 best performers were compared with 10 age-matched control subjects; no differences were found in cardiac index, stroke index, heart rate or blood pressure at any exercise level. Analysis of the determinants of cardiac output showed that at the other end of the spectrum poor performance after a Fontan operation did not result from inadequate levels of heart rate, but from an inability to increase or maintain stroke volume. Multivariate analysis demonstrated that impairment of ventricular contractility, only when severe, predicted limited performance. There was no evidence of increased afterload, particularly in the poor performers. Therefore, ventricular filling, which is determined primarily by the pulmonary vascular bed, appears to be a major determinant of functional result after a Fontan repair.

Transverse arch hypoplasia predisposes to aneurysm formation at the repair site after patch angioplasty for coarctation of the aorta.

OBJECTIVES: This study used magnetic resonance imaging (MRI) to evaluate the morphology and pathophysiology of aneurysm formation after patch angioplasty for coarctation of the aorta. BACKGROUND: Late aneurysm formation at the repair site is a well known and frequent complication after patch angioplasty. However, because the underlying mechanisms remain unresolved, postoperative outcome is unpredictable and adequate follow-up difficult. METHODS: Seventy-three of 85 patients with patch angioplasty for coarctation of the aorta were screened for aneurysm formation. Magnetic resonance imaging was performed in all 33 patients with an aneurysm, and results were compared with those for 13 control patients and 10 normal subjects. Mean (+/- SD) time between operation and MRI was 12.0 +/- 2.0 years. Aneurysm was defined as the ratio of the diameter of the aorta at the repair site to the diaphragmatic aorta > or = 1.5. Hypoplasia of the transverse arch and recoarctation at the repair site were defined as a ratio < 0.9. Transverse arch ratios on MRI were compared with those on preoperative cineangiography and the pressure gradient between the patient's right and left arm. RESULTS: All 33 patients with an aneurysm had a hypoplastic transverse arch. The 13 patients with a normal ratio at the repair site had a normal transverse arch ratio (chi square, p < 0.0001). Logarithmic regression showed a significant negative correlation (r = 0.62) between the repair site and transverse arch ratios. A significant pressure difference between the patient's right and left arm was found in patients with versus those without aneurysm (p = 0.0009). No significant difference was found between transverse arch ratios on preoperative cineangiography and postoperative MRI (mean 0.014 +/- 0.1, p = 0.4). CONCLUSIONS: Aneurysm formation at the repair site is highly related to hypoplasia of the transverse arch. Sufficient catch-up growth of a hypoplastic transverse arch is rare after late patch angioplasty. Dynamic phenomena, such as flow acceleration and turbulence, originating in a narrow transverse arch, may contribute to aneurysm formation at the repair site after patch angioplasty.

PTPN11 mutations in LEOPARD syndrome.

LEOPARD syndrome is an autosomal dominant disorder with multiple lentigines, congenital cardiac abnormalities, ocular hypertelorism, and retardation of growth. Deafness and genital abnormalities are less frequently found. We report a father and daughter and a third, unrelated patient with LEOPARD syndrome. Recently, missense mutations in the PTPN11 gene located in 12q24 were found to cause Noonan syndrome. All three cases of LEOPARD syndrome reported here have a Y279C mutation in the PTPN11 gene. We hypothesise that some PTPN11 mutations are associated with the typical Noonan syndrome phenotype and that other mutations, such as the Y279C mutation reported here, are associated with both the Noonan syndrome phenotype and with skin pigmentation anomalies, such as multiple lentigines or café au lait spots.

Homograft insertion for pulmonary regurgitation after repair of tetralogy of fallot improves cardiorespiratory exercise performance.

Surgical repair of tetralogy of Fallot (TOF) with reconstruction of the right ventricular (RV) outflow tract invariably results in pulmonary regurgitation. Chronic pulmonary regurgitation has been associated with RV dysfunction and decreased exercise performance. The present study assessed the influence of pulmonary valve replacement (PVR) for severe pulmonary regurgitation after previous TOF repair on cardiorespiratory exercise performance and RV function. Eighteen patients, between the ages of 8 and 18 years, underwent an exercise test and a cardiac magnetic resonance imaging scan at least 1 year after PVR. The exercise data were compared with those obtained from 24 age-matched normal controls and 27 age-matched patients with repaired TOF and a moderate degree of pulmonary regurgitation. A subgroup of 11 patients had an exercise test performed before and after PVR. Cardiopulmonary exercise performance was evaluated by determination of the ventilatory anaerobic threshold (VAT) and by the steepness of the slope of oxygen uptake versus exercise intensity (SVO2). After PVR there was a significant increase in VAT (86+/-11% before to 106.9+/-14% after, p = 0.03) and in SVO2 (1.71+/-0.47 to 2.3+/-0.39, p = 0.004). In patients examined after PVR, the VAT and SVO2 values were not significantly different from the values in the normal controls (104+/-15% [p>0.05] and 2.03+/-0.77 after PVR vs. 2.42+/-0.68 [p>0.25], respectively). In contrast, patients with repaired TOF and a moderate degree of pulmonary regurgitation had a significantly lower VAT (86+/-11%, p<0.05) and SVO2 (1.8+/-0.74 vs. 2.42+/-0.68, p<0.05) than normal controls. Magnetic resonance imaging studies revealed residual RV dilatation and dysfunction. However, there was no correlation between RV dilatation and RV dysfunction and aerobic exercise capacity. It is concluded that aerobic exercise capacity substantially improves after PVR for severe pulmonary regurgitation after previous TOF repair. Although the right ventricle remains significantly dilated and hypocontractile, there is no relation between RV function and exercise performance.

A recognisable behavioural phenotype associated with terminal deletions of the short arm of chromosome 8.

We report the clinical findings in 5 patients with a terminal deletion of the short arm of chromosome 8. Mild developmental delay was constantly present, in association with microcephaly in 4 of 5 patients. Facial anomalies were mild or absent. A congenital heart defect was present in 3 patients: an atrioventricular septal defect (AVSD) in 2 and an atrial septal defect type II (ASDII) with pulmonary stenosis in one. A highly similar pattern of behavioural difficulties was present in the 3 older children (8-11 years), with outbursts of aggressiveness and destructive behaviour. Follow-up in one patient showed that at the age of 16 years, these behavioural problems had largely disappeared. This observation suggests that in addition to mental retardation, microcephaly, congenital heart defect (typically AVSD), a terminal deletion of chromosome 8p may be associated with a characteristic behavioural phenotype during childhood.

Recurrent involvement of chromosomal region 6q21 in heterotaxy.

We present a patient with heterotaxy and a de novo, apparently balanced reciprocal translocation with breakpoints at 6q21 and 20p13. Another patient with heterotaxy was previously reported with a de novo balanced translocation involving chromosome band 6q21. The breakpoints in both patients on 6q21 were found to be located in the same chromosomal region spanning maximally 2 Mb. We speculate that the two breakpoints lead to the disruption of the function of a single gene, either directly or through long distance effects. Alternatively, the present observation suggests additional heterogeneity in heterotaxy in humans.

Total cavopulmonary connection: a logical alternative to atriopulmonary connection for complex Fontan operations. Experimental studies and early clinical experience.

To understand better the contribution of a right atrium in a valveless atriopulmonary connection, we performed some basic hydrodynamic studies. Pulsation of a valveless chamber in a simple continuous flow circuit was found to generate turbulence and thereby to increase resistance to net forward flow. Visualization of flow through cavities and around corners and measurements of energy losses across nonpulsatile cavities, corners, and stenoses indicated the importance of streamlining. These studies suggested ways in which hydrodynamic designs of the Fontan circulation might be improved. In parallel with these in vitro studies, we have developed a modified approach to Fontan reconstruction that entails exclusion of most or all of the right atrium (total cavopulmonary connection). The operation consists of three parts: (1) end-to-side anastomosis of the superior vena cava to the undivided right pulmonary artery; (2) construction of a composite intraatrial tunnel with the use of the posterior wall of the right atrium; and (3) use of a prosthetic patch to channel the inferior vena cava to the enlarged orifice of the transected superior vena cava that is anastomosed to the main pulmonary artery. The operation was performed in 20 patients between March 1987 and March 1988. The diagnoses were double-inlet ventricle (11 patients), hypoplastic systemic or pulmonary ventricle (seven patients), and absent right atrioventricular connection (two patients). There were two early deaths and one late death. None of the deaths was related to the actual procedure but rather to increased pulmonary vascular resistance (two patients) or systemic ventricular failure (one patient). Total cavopulmonary connections have the following advantages: (1) They are technically simple and reproducible in any atrioventricular arrangement and are away from the atrioventricular node; (2) most of the right atrial chamber remains at low pressure, which reduces the risk of early or late arrhythmias; (3) reduction of turbulence prevents energy losses and should minimize the risk of atrial thrombosis; (4) postoperative cardiac catheterization performed in 10 patients confirmed these favorable flow patterns with minimal gradients throughout the connections. These encouraging early results support the continuing use of total cavopulmonary connection, at least for patients with a nonhypertrophied right atrium.

Protein-losing enteropathy after the Fontan operation: an international multicenter study. PLE study group.

OBJECTIVE: This multicenter study retrospectively analyzes the data on 114 patients with protein-losing enteropathy after Fontan-type surgery. Special attention was given to the different treatment strategies used and their effect on outcome. METHODS AND RESULTS: In 35 participating centers 3029 Fontan operations were performed. The incidence of protein-losing enteropathy in the survivors was 3.7%. The median age at Fontan-type surgery was 8.2 years (range: 0.6 to 32.9 years). Median age at diagnosis of protein-losing enteropathy was 11.7 years with a median time interval between surgery and diagnosis of 2.7 years (range: 0.1 to 16.4 years). Most patients had edema (79%) and effusions (75%). Hemodynamic data revealed a mean right atrial pressure of 17 +/- SD 5.3 mm Hg with a cardiac index of 2.4 +/- 0.8 L/min/m2. Medical treatment only (n = 52) resulted in a complete resolution of symptoms in 25%, no improvement in 29%, and death in 46%. Surgical treatment (n = 52) was associated with relief of protein-losing enteropathy in 19%, no improvement in 19%, and death in 62%. In 13 patients 16 percutaneous interventions were performed. This resulted in symptomatic improvement after 12 interventions and no improvement after 4 interventions. CONCLUSIONS: We conclude that the current treatment of protein-losing enteropathy after Fontan operation is associated with a very high mortality and morbidity rate. Preventive strategies and new therapeutic approaches are necessary.

Dynamics of respiratory gas exchange during exercise after correction of congenital heart disease.

In pediatric exercise testing, conventional measures of aerobic exercise function such as maximal O2 uptake or the ventilatory anaerobic threshold (VAT) use only one value for the assessment of exercise capacity. We studied a more comprehensive approach to evaluate aerobic exercise function by analyzing the steepness of the slope of CO2 production (VCO2) vs. VO2 above the VAT (S3). This was calculated in 32 patients operated on for congenital heart disease [16 for transposition of the great arteries (TGA) and 16 for tetralogy of Fallot (TF)] and was compared with 16 age-matched controls (nl). The results show that the reproducibility of this new assessment method was excellent (coefficient of variation for S3: 8.6%). S3 was significantly steeper (P<0.05) in the patients (1.31 +/- 0.22 for TGA and 1.28 +/- 0.16 for TF) compared with the nl (1.10 +/- 0.22). Also, the difference between S3 and the slope of VCO2 vs. VO2 below the VAT was significantly higher in the patients (0.37 +/- 0.22 for TGA and 0.31 +/- 0.10 for TF) than in controls (0.22 +/- 0.06). The steeper slopes were associated with lower than normal values for VAT and O2 during exercise. It is concluded that the analysis of the steepness of the slope of CO2 is a sensitive, reproducible, and objective approach to evaluate the integrative cardiopulmonary response to exercise. It complements the assessment of a subnormal VAT by reflecting the extent of anaerobic metabolism.