Endothelial function following the Fontan operation

Decreased erythrocyte aggregation in Glenn and Fontan: univentricular circulation as a rheologic disease model

BACKGROUND

In the Fontan palliation for single ventricle heart disease (SVHD), pulmonary blood flow is non-pulsatile/passive, low velocity, and low shear, making viscous power loss a critical determinant of cardiac output. The rheologic properties of blood in SVHD patients are essential for understanding and modulating their limited cardiac output and they have not been systematically studied. We hypothesize that viscosity is decreased in single ventricle circulation.

METHODS

We evaluated whole blood viscosity, red blood cell (RBC) aggregation, and RBC deformability to evaluate changes in healthy children and SVHD patients. We altered suspending media to understand cellular and plasma differences contributing to rheologic differences.

RESULTS

Whole blood viscosity was similar between SVHD and healthy at their native hematocrits, while viscosity was lower at equivalent hematocrits for SVHD patients. RBC deformability is increased, and RBC aggregation is decreased in SVHD patients. Suspending SVHD RBCs in healthy plasma resulted in increased RBC aggregation and suspending healthy RBCs in SVHD plasma resulted in lower RBC aggregation.

CONCLUSIONS

Hematocrit corrected blood viscosity is lower in SVHD vs. healthy due to decreased RBC aggregation and higher RBC deformability, a viscous adaptation of blood in patients whose cardiac output is dependent on minimizing viscous power loss.

IMPACT

Patients with single ventricle circulation have decreased red blood cell aggregation and increased red blood cell deformability, both of which result in a decrease in blood viscosity across a large shear rate range. Since the unique Fontan circulation has very low-shear and low velocity flow in the pulmonary arteries, blood viscosity plays an increased role in vascular resistance, therefore this work is the first to describe a novel mechanism to target pulmonary vascular resistance as a modifiable risk factor. This is a novel, modifiable risk factor in this patient population.

Exploring the Promise of Telemedicine Exercise Interventions in Children and Adolescents With Congenital Heart Disease

Youth with congenital heart disease (CHD) have reduced exercise capacity via various physical and psychosocial mechanisms. In addition to limited physiologic exercise capacity, these patients experience lower levels of physical activity, physical activity self-efficacy, health-related quality of life, and endothelial function. The study of exercise interventions and cardiac rehabilitation programs in pediatric CHD populations remains limited, particularly home-based interventions that incorporate real-time physiologic monitoring. Home-based interventions provide improved access and convenience to patients. This is principally important for patients from geographically disperse regions who receive their care at centralized subspecialty centres, as is the case for Canadian pediatric cardiac care. These programs, however, have traditionally not permitted the supervision of safety, technique, and adherence that are afforded by hospital/facility-based programs. As such, telemedicine is an important evolving area that combines the benefits of traditional home and facility-based cardiac rehabilitation. An additional key area lacking study surrounds the types of exercise interventions in youth with CHD. To date, interventions have often centred around moderate-intensity continuous exercise. High-intensity interval training might offer superior cardiorespiratory advantages but remains understudied in the CHD population. In this review, we highlight the existing evidence basis for exercise interventions in youth with CHD, explore the promise of incorporating telemedicine home-based solutions, and highlight key knowledge gaps. To address identified knowledge gaps, we are undertaking a 12-week randomized crossover trial of a home-based telemedicine high-intensity interval training intervention in youth with repaired moderate-severe CHD using a video game-linked cycle ergometer (known as the MedBIKE; https://spaces.facsci.ualberta.ca/ahci/projects/medical-projects/remote-rehab-bike-projects).

Design and rationale of re-energize fontan: Randomized exercise intervention designed to maximize fitness in fontan patients

In this manuscript, we describe the design and rationale of a randomized controlled trial in pediatric Fontan patients to test the hypothesis that a live-video-supervised exercise (aerobic+resistance) intervention will improve cardiac and physical capacity; muscle mass, strength, and function; and endothelial function. Survival of children with single ventricles beyond the neonatal period has increased dramatically with the staged Fontan palliation. Yet, long-term morbidity remains high. By age 40, 50% of Fontan patients will have died or undergone heart transplantation. Factors that contribute to onset and progression of heart failure in Fontan patients remain incompletely understood. However, it is established that Fontan patients have poor exercise capacity which is associated with a greater risk of morbidity and mortality. Furthermore, decreased muscle mass, abnormal muscle function, and endothelial dysfunction in this patient population is known to contribute to disease progression. In adult patients with 2 ventricles and heart failure, reduced exercise capacity, muscle mass, and muscle strength are powerful predictors of poor outcomes, and exercise interventions can not only improve exercise capacity and muscle mass, but also reverse endothelial dysfunction. Despite these known benefits of exercise, pediatric Fontan patients do not exercise routinely due to their chronic condition, perceived restrictions to exercise, and parental overprotection. Limited exercise interventions in children with congenital heart disease have demonstrated that exercise is safe and effective; however, these studies have been conducted in small, heterogeneous groups, and most had few Fontan patients. Critically, adherence is a major limitation in pediatric exercise interventions delivered on-site, with adherence rates as low as 10%, due to distance from site, transportation difficulties, and missed school or workdays. To overcome these challenges, we utilize live-video conferencing to deliver the supervised exercise sessions. Our multidisciplinary team of experts will assess the effectiveness of a live-video-supervised exercise intervention, rigorously designed to maximize adherence, and improve key and novel measures of health in pediatric Fontan patients associated with poor long-term outcomes. Our ultimate goal is the translation of this model to clinical application as an "exercise prescription" to intervene early in pediatric Fontan patients and decrease long-term morbidity and mortality.

Mild Acquired von Willebrand Syndrome and Cholestasis in Pediatric and Adult Patients with Fontan Circulation

Background: Hemodynamic alterations in Fontan patients (FP) are associated with hemostatic dysbalance and Fontan-associated liver disease. Studies of other hepatopathologies indicate an interplay between cholestasis, tissue factor (TF), and von Willebrand factor (VWF). Hence, we hypothesized a relationship between the accumulation of bile acids (BA) and these hemostatic factors in FP. Methods: We included 34 FP (Phenprocoumon n = 15, acetylsalicylic acid (ASA) n = 16). BA were assessed by mass spectrometry. TF activity and VWF antigen (VWF:Ag) were determined by chromogenic assays. VWF collagen-binding activity (VWF:CB) was assessed via ELISA. Results: Cholestasis was observed in 6/34 FP (total BA ≥ 10 µM). BA levels and TF activity did not correlate (p = 0.724). Cholestatic FP had lower platelet counts (p = 0.013) from which 5/6 FP were not treated with ASA. VWF:Ag levels were increased in 9/34 FP and significantly lower in FP receiving ASA (p = 0.044). Acquired von Willebrand syndrome (AVWS) was observed in 10/34-FP, with a higher incidence in cholestatic FP (4/6) (p = 0.048). Conclusions: Cholestasis is unexpectedly infrequent in FP and seems to be less frequent under ASA therapy. Therefore, ASA may reduce the risk of advanced liver fibrosis. FP should be screened for AVWS to avoid bleeding events, especially in cholestatic states.

Diminished Endothelial Function but Normal Vascular Structure in Adults with Tetralogy of Fallot

The life expectancy of patients with Tetralogy of Fallot (ToF) has increased in recent years. As a result, other risk factors with later onset in life are in the focus of patient care. Endothelial function is an early indicator of cardiovascular risk and was investigated along further structural vessel properties. A total of 17 patients (41.7 ± 7.1 years, 8 women) with Tetralogy of Fallot were 1:2 matched for sex with 34 (38.9 ± 8.1 years, 16 women) healthy volunteers. Participants received an assessment of their endothelial function and a structural assessment of the aorta. Patients with ToF showed a reduced endothelial function determined by reactive hyperaemia index after adjusting for age, weight and height (ToF: 1.55 ± 0.31 vs. controls: 1.84 ± 0.47; p = 0.023). No differences in carotid intima-media thickness (cIMT) between the ToF and healthy controls (ToF: 0.542 ± 0.063 mm vs. controls: 0.521 ± 0.164 mm; p = 0.319) were found. Patients with ToF had reduced vascular function compared to healthy subjects. As the structural component is not affected, endothelial dysfunction seems not to have yet manifested itself as a morphological change. Nevertheless, long-term management of these patients should include vascular parameters.

3-Month Enalapril Treatment in Pediatric Fontan Patients With Moderate to Good Systolic Ventricular Function

Many Fontan patients with and without systolic ventricular dysfunction are being treated with angiotensin-converting enzyme (ACE) inhibitors, despite its effectiveness remaining unclear. In the present study, we evaluated the short-term effect of enalapril on exercise capacity, vascular and ventricular function in pediatric Fontan patients with moderate-good systolic ventricular function. Fontan patients between 8 and 18 years with moderate-good systolic ventricular function and without previous ACE inhibitor treatment were included and were treated with enalapril for 3 months. During the first 2 weeks, the dosage was titrated according to systolic blood pressure (SBP). Exercise tests, ventricular function assessed by echocardiography, arterial stiffness measurements, and plasma levels of N-terminal pro-B-type natriuretic peptide assessed before and after a 3-month enalapril treatment period was compared. A total of 28 Fontan patients (median age 13.9 years, 6 to 15 years after Fontan operation) completed the study with a mean dosage of 0.3 ± 0.1 mg/kg/d. A total of 6 patients (21%) experienced a significant drop in SBP and 6 others (21%) experienced other adverse events. Enalapril treatment lowered the SBP (from 110 to 104 mmHg, p = 0.003) and levels of N-terminal pro-B-type natriuretic peptide (from 80 to 72 ng/L, p = 0.036). However, enalapril treatment did not improve exercise capacity, ventricular function, or arterial stiffness. In conclusion, short-term ACE inhibition has no beneficial effect in Fontan patients with moderate-good systolic ventricular function.

Increased Risk for Thromboembolism After Fontan Surgery: Considerations for Thromboprophylaxis

The Fontan circulation introduces an increased risk of thromboembolism which is associated with substantial mortality and morbidity. Adverse outcomes of thromboembolic complications post-Fontan surgery vary in both nature and severity, ranging from local tissue infarction and pulmonary embolism to Fontan failure and ischemic stroke. Furthermore, recent studies have identified that subclinical stroke is common yet underdiagnosed in Fontan patients. Fontan patients are commonly treated with antiplatelet agents and/or anticoagulants as primary thromboprophylaxis. Optimal thromboprophylaxis management in the Fontan population is still unclear, and clinical consensus remains elusive despite the growing literature on the subject. This perspective will describe the nature of thromboembolism post-Fontan surgery and provide evidence for the use of both current and emerging thromboprophylaxis options for children and adults living with Fontan circulation.

Hemodynamic and Clinical Implications of Impaired Pulmonary Vascular Reserve in the Fontan Circulation

BACKGROUND

Pulmonary vascular disease, pulmonary endothelial dysfunction, liver fibrosis, renal disease, and exercise intolerance are common in adults with Fontan physiology. Although the pathophysiologic mechanisms linking these phenomena have been studied, certain aspects are not well understood.

OBJECTIVES

This study hypothesized that impaired pulmonary vascular reserve (VR) plays a central role linking these abnormalities, and that patients with abnormal pulmonary VR with exercise, compared with patients with normal VR, would display poorer pulmonary endothelial function, greater liver stiffness, more renal dysfunction, and poorer exercise capacity.

METHODS

Symptomatic adults with the Fontan palliation (n = 29) underwent invasive cardiopulmonary exercise testing, echocardiography, and assessment of microvascular function. Abnormal pulmonary VR was defined by the slope of increase in pulmonary pressure relative to cardiac output with exercise >3 mm Hg/l/min. Pulmonary endothelial function was assessed using reactive hyperemia index. End-organ function was assessed using magnetic resonance elastography-derived liver stiffness, glomerular filtration rate, N-terminal pro-B-type natriuretic peptide, and peak oxygen consumption (Vo₂).

RESULTS

Compared with individuals with normal VR (n = 8), those with abnormal VR (n = 21) displayed higher central and pulmonary venous pressures, and more severely impaired cardiac output and stroke volume responses to exertion, but similar pulmonary vascular resistance at rest. Patients with abnormal VR displayed more severely impaired reactive hyperemia index, increased liver stiffness, lower glomerular filtration rate, higher N-terminal pro-B-type natriuretic peptide, and lower peak Vo₂. As compared to pulmonary vascular resistance at rest, slope of increase in pulmonary pressure relative to cardiac output displayed stronger correlations with reactive hyperemia index (r = -0.63 vs. r = -0.31; Meng test p = 0.009), magnetic resonance elastography-derived liver stiffness (r = 0.47 vs. r = 0.29; Meng test p = 0.07), glomerular filtration rate (r = -0.52 vs. r = -0.24; Meng test p = 0.03), N-terminal pro-B-type natriuretic peptide (r = 0.56 vs. r = 0.17; Meng test p = 0.02), and peak Vo₂ (r = -0.63 vs. r = -0.26; Meng test p = 0.02).

CONCLUSIONS

Pulmonary vascular limitations in Fontan physiology are related to pulmonary endothelial and end-organ dysfunction, suggesting a mechanistic link between these commonly observed findings, and these abnormalities are more apparent during exercise testing, with little relationship at rest.

Thromboembolic complications in adult congenital heart disease: the knowns and the unknowns

Despite impressive improvement in long-term survival, adults with congenital heart disease (CHD) remain exposed to a significant cardiovascular morbidity over lifetime. Thromboembolic events (TE) are a major issue. Specific anatomic groups have been shown a particular high risk of TE, including cyanotic heart disease and Fontan circulation. Many intercurrent clinical factors add a substantial risk such as intracardiac medical devices, atrial arrhythmia, endocarditis, or pregnancy. Nevertheless, what is unknown exceeds what is known, especially regarding the management of this heterogenous patient population. Anticoagulation decision should always be individualized weighing balanced with the alternative risk of hemorrhagic complications. In this review, we aim to synthetize existing literature on TE in adults with CHD, discuss management issues, highlight gaps in knowledge, and intend to suggest high priority research.

Tissue oxygen saturation assessment of microvascular perfusion in adults with Fontan palliation and comparator groups using vascular optical spectrophotometry: a pilot study

OBJECTIVE

The Fontan operation greatly improves survival for single ventricle congenital heart disease patients but creates a physiology that leads to long-term multi-organ dysfunction. A non-invasive screening tool that can identify impending decline is sought. The objective of this pilot study was to assess the microcirculation in Fontan-palliated patients by measuring tissue oxygen saturation (StO₂) in superficial and deeper tissues.

APPROACH

Three patient cohorts were studied: Fontan group (n  =  8) and two patient control groups, liver disease group (n  =  8) and tetralogy of Fallot group (n  =  9). 22 healthy controls were also examined. Superficial and deeper StO₂ was measured at the forearm, thenar eminence, index and ring fingers of both arms using the LEA O2C spectrophotometry device.

MAIN RESULTS

Superficial StO₂ was reduced in Fontan patients compared to healthy controls (p   =  0.002) and tetralogy patients (p   =  0.016), but not compared to the liver group (p   =  0.313). Deeper StO₂ was similar between groups (p   =  0.112). The gap between deeper and superficial StO₂ was raised in Fontan patients compared to healthy controls (p   =  0.001) and tetralogy patients (p   =  0.037), but not compared to the liver group (p   =  0.504). There was no clinically relevant difference in StO₂ between the left and right arms, and the variation in StO₂ according to measurement site was similar between the four groups.

SIGNIFICANCE

Vascular optical spectrophotometry is a feasible non-invasive measure of micro-circulatory function that can easily be performed in the clinic setting and may have utility in patients with Fontan circulations. Further, we provide important normal range data in the healthy control population which can be used to design future studies.

Arterial Stiffness and Its Relationship to Cardiorespiratory Fitness in Children and Young Adults with a Fontan Circulation

There are no previous studies on arterial stiffness and its associations with cardiorespiratory fitness in young Fontan patients. Therefore, we examined the arterial stiffness and its relationship to cardiorespiratory fitness in children and young adults with a Fontan circulation. Altogether, 17 Fontan patients and 26 healthy controls (16 females and 27 males aged 8-40 years) participated in this cross-sectional study. The cardiorespiratory fitness was assessed by cardiopulmonary exercise testing on a cycle ergometer and was defined as the standard deviation scores (SDS) of peak oxygen uptake per body mass (VO_2peak/kg) based on the national reference values and assessed with cardiopulmonary exercise testing on a cycle ergometer. Aortic pulse wave velocity (PWV_ao) as a measure of arterial stiffness and aortic Augmentation Index (AIX) as a measure of peripheral arterial tone, were assessed by non-invasive oscillometric device from upper arm. Body adiposity was determined by body mass index SDS and the sport participation by interview. Data were analyzed using linear regression analyses and Pearson's correlations, adjusted for age and sex. Fontan patients had a lower VO_2peak/kg-SDS (- 2.69 vs 0.078), higher PWV_ao-SDS (1.13 vs - 0.24) and higher AIX (19.26% vs 8.49%) in comparison with healthy controls. PWV_ao and AIX were negatively associated with VO_2peak/kg (standard regression coefficient (β) - 0.525, 95% confidence interval (CI) - 0.722 to - 0.227, p < 0.01 and β - 0.371, 95% CI - 0.672 to - 0.080, p = 0.014). Young Fontan patients have the arterial stiffness of healthy people who are twice as old. Thereby, children and young adults with a Fontan circulation have a lower cardiorespiratory fitness and less sport participation. Arterial stiffness is inversely associated with cardiorespiratory fitness and exercise training might be an intervention to improve vascular health in this population.

Diagnosis and Management of Noncardiac Complications in Adults With Congenital Heart Disease: A Scientific Statement From the American Heart Association

Life expectancy and quality of life for those born with congenital heart disease (CHD) have greatly improved over the past 3 decades. While representing a great advance for these patients, who have been able to move from childhood to successful adult lives in increasing numbers, this development has resulted in an epidemiological shift and a generation of patients who are at risk of developing chronic multisystem disease in adulthood. Noncardiac complications significantly contribute to the morbidity and mortality of adults with CHD. Reduced survival has been documented in patients with CHD with renal dysfunction, restrictive lung disease, anemia, and cirrhosis. Furthermore, as this population ages, atherosclerotic cardiovascular disease and its risk factors are becoming increasingly prevalent. Disorders of psychosocial and cognitive development are key factors affecting the quality of life of these individuals. It is incumbent on physicians who care for patients with CHD to be mindful of the effects that disease of organs other than the heart may have on the well-being of adults with CHD. Further research is needed to understand how these noncardiac complications may affect the long-term outcome in these patients and what modifiable factors can be targeted for preventive intervention.

Histopathological abnormalities in the central arteries and veins of Fontan subjects

OBJECTIVE

Fontan circulations have obligatory venous hypertension, depressed cardiac output and abnormal arterial elastance. Ventriculovascular coupling is known to be abnormal, but the underlying mechanisms are poorly defined. We aim to describe the histopathological features of vascular remodelling encountered in the central arteries and veins in the Fontan circulation as a possible underlying pathological representation of abnormal ventriculovascular coupling.

METHODS

Postmortemvasculature (inferior vena cava (IVC), superior vena cava (SVC), pulmonary artery (PA), pulmonary vein (PV) and aorta) of 13 patients with a Fontan circulation (mean age 29.9 years, range 9.0-59.8 years) and 2 biventricular controls (ages 17.9 and 30.2 years) was examined.

RESULTS

IVC and SVC: Eccentric and variable intimal fibromuscular proliferation occurred in 11 Fontan subjects. There was variable loss of medial smooth muscle bundles with reciprocal replacement with dense collagenous tissue.PA: Similar intimal fibromuscular proliferation was seen; however, these intimal changes were accompanied by medial thinning rather than expansion, medial myxoid degeneration and elastic alteration.PV: The PVs demonstrated intimal fibroproliferation and disorganisation of the muscular media.Aorta: The aortic lamina intima was thickened, with associated fibromuscular proliferation and elasticisation. There was also moderate lymphocytic inflammation in the aortic wall.

CONCLUSIONS

Vascular architectural remodelling is common in Fontan patients. The central veins demonstrate profound changes of eccentric intimal expansion and smooth muscle replacement with collagen. The pulmonary demonstrated abnormal intimal proliferation, and aortic remodelling was characterised by intima lamina thickening and a moderate degree of aortic wall inflammation.

Endothelial Function and Arterial Stiffness Relate to Functional Outcomes in Adolescent and Young Adult Fontan Survivors

Background

Fontan survivors demonstrate diminished vascular function and functional outcomes, but the relationships between these measures have not been established.

Methods and Results

We performed a cross‐sectional study of 60 Fontan survivors (52% male) with a mean age of 13.9±4.1 years and mean Fontan duration of 9.9±4.2 years. Multimodality assessment of endothelial function (reactive hyperemia index and flow‐mediated dilation) and arterial stiffness (augmentation index and baseline pulse amplitude) was performed with peripheral arterial tonometry and brachial flow‐mediated dilation. Aerobic capacity was determined using cardiopulmonary exercise testing; mean peak and percentage of predicted oxygen consumption (VO₂) were 27.8±7.6 mL/kg per minute and 71.0±21.2%, respectively. Quality of life and physical activity were assessed using the Pediatric Quality of Life Inventory (PedsQL) and the Physical Activity Questionnaire. Vascular measures served as predictor variables, whereas functional measures served as outcome variables. In all cases, worse vascular measures were associated with worse functional measures. Flow‐mediated dilation–derived reactive hyperemia index (P<0.05) was positively associated with VO₂ at anaerobic threshold. Peripheral arterial tonometry–derived baseline pulse amplitude (P<0.05) was negatively associated with the ratio of minute ventilation to carbon dioxide at anaerobic threshold. Flow‐mediated dilation–derived reactive hyperemia index and peripheral arterial tonometry–derived augmentation index (P<0.05) were positively and negatively associated, respectively, with peak VO₂. Maximum flow‐mediated dilation (P<0.05) was positively associated with Physical Activity Questionnaire score. Peripheral arterial tonometry–derived augmentation index and baseline pulse amplitude (P<0.05) were negatively associated with parent‐reported PedsQL total and physical heath summary scores.

Conclusions

Increased arterial stiffness and decreased endothelial function are associated with lower aerobic capacity, physical activity, and quality of life in adolescent and young adult Fontan survivors. Understanding the cause–effect relationship between vascular function and functional outcomes is an important next step.

Posterior reversible encephalopathy syndrome after pediatric heart transplantation: Increased risk for children with preexisting Glenn/Fontan physiology

Identification of risk factors for PRES after organ transplant can improve early detection and avoid permanent neurological injury. High calcineurin-inhibitor levels and hypertension are recognized risk factors for PRES in adult transplant recipients. Limited data exist regarding PRES after pediatric HTx, with studies limited to case reports. We performed a retrospective review of 128 pediatric HTx recipients to identify risk factors for PRES. Seven of 128 (5.5%) recipients developed PRES at a median of 10 days (5-57) after HTx. The median age of recipients with PRES was 10.0 yr (5.7-19.0), compared to 1.4 yr (0.0-19.8) for recipients without PRES (p = 0.010). Fewer than half of recipients with PRES had elevated post-transplant calcineurin-inhibitor levels (n = 3) and/or preceding severe hypertension (n = 3). Four of seven who developed PRES (57%) had pretransplant Glenn or Fontan physiology (G/F). G/F was a significant risk factor for PRES (RR 4.99, 95% CI: 1.19-21.0, p = 0.036). Two recipients (29%), both with severe PRES, had residual neurological symptoms. In summary, PRES occurred in 5.5% of pediatric HTx recipients and presented early after HTx. All recipients with PRES were > 5 yr. Patients with pretransplant G/F were at increased risk, a risks factor not previously described.

Total Cavopulmonary Connection is Superior to Atriopulmonary Connection Fontan in Preventing Thrombus Formation: Computer Simulation of Flow-Related Blood Coagulation

The classical Fontan route, namely the atriopulmonary connection (APC), continues to be associated with a risk of thrombus formation in the atrium. A conversion to a total cavopulmonary connection (TCPC) from the APC can ameliorate hemodynamics for the failed Fontan; however, the impact of these surgical operations on thrombus formation remains elusive. This study elucidates the underlying mechanism of thrombus formation in the Fontan route by using a two-dimensional computer hemodynamic simulation based on a simple blood coagulation rule. Hemodynamics in the Fontan route was simulated with Navier-Stokes equations. The blood coagulation and the hemodynamics were combined using a particle method. Three models were created: APC with a square atrium, APC with a round atrium, and TCPC. To examine the effects of the venous blood flow velocity, the velocity at rest and during exercise (0.5 and 1.0 W/kg) was measured. The total area of the thrombi increased over time. The APC square model showed the highest incidence for thrombus formation, followed by the APC round, whereas no thrombus was formed in the TCPC model. Slower blood flow at rest was associated with a higher incidence of thrombus formation. The TCPC was superior to the classical APC in terms of preventing thrombus formation, due to significant blood flow stagnation in the atrium of the APC. Thus, local hemodynamic behavior associated with the complex channel geometry plays a major role in thrombus formation in the Fontan route.

Elevated Aortic Augmentation Index in Children Following Fontan Palliation: Evidence of Stiffer Arteries?

Children born with a functional single ventricle who undergo Fontan palliation are prone to early pump failure. Whether they develop early arterial stiffness with resultant increase in afterload is not well known. We hypothesized that the aortic stiffness is higher in pediatric Fontan patients when compared to healthy controls. A prospective study was conducted at the Children's Hospital of Michigan. Twenty-two Fontan patients (aged 6-21 years) were compared with 22 healthy controls (aged 9-17 years) selected from children referred to our clinic who had normal cardiac anatomy and function on the echocardiogram. Aortic stiffness was assessed noninvasively by measuring the aortic augmentation index (AAI) using applanation tonometry (Sphygmocor, Atcor, IL). AAI was calculated as AP/PP where augmentation pressure (AP) is the increase in aortic systolic blood pressure (BP) and pulse pressure (PP) is the difference between aortic systolic and diastolic BP. Ten patients (45 %) had hypoplastic left ventricle, and 11 (50 %) had undergone aortic arch surgery. The median AAI was significantly higher in Fontan patients when compared to controls (12.5, IQR 4.8, 17.3 vs 0, IQR -6.3, 5.8; p = 0.0003). History of aortic arch surgery and single ventricle morphology did not have a significant impact on AAI. Pediatric patients who undergo Fontan palliation have significantly higher AAI, a marker of aortic stiffness and increased afterload, compared to healthy controls. Larger longitudinal studies are warranted to elucidate the possible contribution of elevated AAI on pump failure in these patients.

Long-term Issues After the Fontan Procedure

The Fontan procedure is used to treat various serious congenital heart defects. Although many people who have had the procedure live productively into adulthood, as they age, they face several health issues due to the physiology of the Fontan circulation. This article reviews the 4 types of Fontan procedures and the changes caused by the surgery, including single-ventricle physiology, nonpulsatile pulmonary perfusion, systemic venous hypertension, and intracardiac scarring, as well as their sequelae. Key nursing assessment items and possible treatment strategies are reviewed. Additional topics, including pregnancy in patients who have undergone the procedure, infective endocarditis prophylaxis, and health-related quality of life, are briefly discussed. Options for Fontan failure, including Fontan conversion or transplantation, are presented. Potential future solutions are outlined.

Sildenafil exposure and hemodynamic effect after stage II single-ventricle surgery

OBJECTIVES

To determine sildenafil exposure and hemodynamic effect in children after stage II single-ventricle surgery.

DESIGN

Prospective, dose escalation trial.

SETTING

Single-center, pediatric catheterization laboratory.

PATIENTS

Twelve children poststage II single-ventricle surgical palliation and undergoing elective cardiac catheterization: median age 1.9 years (range, 0.8, 4.0), weight 11 kg (8, 13), nine females, and 10 with a single right ventricle.

INTERVENTIONS

Catheterization and echocardiography performed before and immediately after single-dose IV sildenafil (0.125, 0.25, 0.35, or 0.45 mg/kg over 20 min).

MEASUREMENTS

Peak sildenafil and desmethyl sildenafil concentration, change in hemodynamic parameters measured by cardiac catheterization and echocardiography including indexed pulmonary vascular resistance, and myocardial performance.

MAIN RESULTS

Maximum sildenafil concentrations ranged from 92 to 775 ng/mL and were above the in vitro threshold needed for 77% phosphodiesterase type 5 (PDE-5) inhibition in 80% of subjects and 90% inhibition in 80% of subjects with doses ≥0.35 mg/kg. Sildenafil lowered pulmonary vascular resistance index in all 12 subjects (median pulmonary vascular resistance index 2.2 [range, 1.6, 7.9]; decreased to 1.7 [1.2, 5.4] WU × m; p < 0.01) with no dose-response effect. Sildenafil improved pulmonary blood flow (+8% [0, 20], p = 0.04) and saturations (+2% [0, 16], p = 0.04) in those with baseline pulmonary vascular resistance index ≥ 2 WU × m (n = 7). Change in saturations correlated inversely with change in pulmonary vascular resistance index (r = 0.74, p < 0.01). Sildenafil also lowered mean blood pressure (-12% [-20, +10]; p = 0.04). There was no change in cardiac index and no effect on myocardial performance. There were no adverse events.

CONCLUSIONS

Sildenafil demonstrated nonlinear exposure with high interindividual variability but was well tolerated and effectively lowered pulmonary vascular resistance index in all subjects. Sildenafil did not acutely improve myocardial performance or increase cardiac index.

Thromboembolic complications in Fontan patients: population-based prevalence and exploration of the etiology

After the Fontan procedure, patients face an increased risk for thromboembolic events (TE). The etiology for this increased thrombogenecity is incompletely understood. This study aimed to determine the prevalence of TE in Danish Fontan patients and to bring new insights into the etiology of TE. Using a population-based design, we retrospectively identified all TEs in 210 Fontan patients. Whole blood assays (thromboelastography, thromboelastography functional fibrinogen and Multiplate) reflecting global hemostasis, clot strength and platelet aggregation were analyzed prospectively in 112 patients and plasma was analyzed in 76 patients for biomarkers reflecting endothelial-, glycocalyx-, platelet-, and fibrinolysis function (histone-complexed DNA fragments, Protein C, soluble CD40 ligand, soluble thrombomodulin, syndecan-1, tissue-type plasminogen activator). The results were compared in groups stratified according to age, antithrombotic therapy, TE, and glycocalyx degradation (syndecan-1 < or ≥ median). Correlation between biomarkers and demographic-, anatomical-, clinical- and biochemical parameters was investigated. The prevalence of TE was 8.1 % after a mean follow-up of 8.4 years. None of the stratified groups demonstrated evidence of hypercoagulability in the whole blood assays and no unexpected significant differences were found between the groups. All biomarkers, except protein C, correlated with one another and after stratification of glycocalyx degradation only syndecan-1 levels ≥ median correlated with other biomarkers. The prevalence of TEs was 8.1 % after mean follow-up of 8.4 years. Overall, the hemostatic profile appeared normal, however, in a subset of patients, evidence of some endothelial activation/damage including glycocalyx degradation and fibrinolysis was found, identifying a potentially more thrombogenic group.

Assessment of vascular remodeling after the Fontan procedure using a novel very high resolution ultrasound method: arterial wall thinning and venous thickening in late follow-up

The Fontan circulation is associated with an increased central venous pressure, decreased ventricular preload, and increased afterload. We postulated that these central hemodynamic abnormalities would have consequences for the structural and functional properties of the peripheral arteries and veins, and performed a cross-sectional study in a tertiary health-care setting. We prospectively examined venous and arterial wall morphology by very high resolution ultrasound (VHRU, 25-55 MHz), and function by conventional vascular ultrasound (flow-mediated dilatation, FMD) and applanation tonometry (pulse wave velocity, PWV) in 28 patients after the Fontan procedure (age 14.8 ± 1.3 years) and 54 age-matched controls. Pig venous samples were studied with VHRU and compared with histology for accuracy. The precision of the venous VHRU method was studied in healthy volunteers. The lumen dimension was reduced in Fontans compared with controls in the common carotid, brachial, radial, and femoral arteries (p < 0.05). The common carotid, brachial, radial, ulnar, femoral, and dorsal tibial artery intima-media thicknesses (IMTs) and the brachial, ulnar, and femoral artery adventitial thicknesses were decreased (p < 0.05 for all), while the cubital and dorsal tibial vein IMTs were increased in Fontans (p < 0.001). FMD, abdominal aortic stiffness, and carotid-femoral PWV were similar, while carotid-radial artery PWV was increased in Fontans (p < 0.01). Venous wall layer assessment with VHRU was accurate and precise. The Fontan circulation is associated with significant arterial and venous remodeling, presumably reflecting abnormalities of central hemodynamics. These novel data may be of clinical importance in the circulatory management as well as the understanding of the early pathogenesis of vasculopathy in patients after the Fontan procedure.

Hypoplastic left heart syndrome: current considerations and expectations

In the recent era, no congenital heart defect has undergone a more dramatic change in diagnostic approach, management, and outcomes than hypoplastic left heart syndrome (HLHS). During this time, survival to the age of 5 years (including Fontan) has ranged from 50% to 69%, but current expectations are that 70% of newborns born today with HLHS may reach adulthood. Although the 3-stage treatment approach to HLHS is now well founded, there is significant variation among centers. In this white paper, we present the current state of the art in our understanding and treatment of HLHS during the stages of care: 1) pre-Stage I: fetal and neonatal assessment and management; 2) Stage I: perioperative care, interstage monitoring, and management strategies; 3) Stage II: surgeries; 4) Stage III: Fontan surgery; and 5) long-term follow-up. Issues surrounding the genetics of HLHS, developmental outcomes, and quality of life are addressed in addition to the many other considerations for caring for this group of complex patients.

Congenital Heart Defects in Adults : A Field Guide for Cardiologists

Advances in cardiology and cardiac surgery allow a large proportion of patients with congenital heart defects to survive into adulthood. These patients frequently develop complications characteristic of the defect or its treatment. Consequently, adult cardiologists participating in the care of these patients need a working knowledge of the more common defects. Occasionally, patients with congenital heart defects such as atrial septal defect, Ebstein anomaly or physiologically corrected transposition of the great arteries present for the first time in adulthood. More often patients previously treated in pediatric cardiology centers have transitioned to adult congenital heart disease centers for ongoing care. Some of the more important defects in this category are tetralogy of Fallot, transposition of the great arteries, functionally single ventricle defects, and coarctation. Through this field guide, we provide an overview of the anatomy of selected defects commonly seen in an adult congenital practice using pathology specimens and clinical imaging studies. In addition, we describe the physiology, clinical presentation to the adult cardiologist, possible complications, treatment options, and outcomes.

Impact of vitamin C on endothelial function and exercise capacity in patients with a Fontan circulation

OBJECTIVE

  To evaluate the impact of antioxidant therapy on functional health status in Fontan-palliated patients. Design.  Prospective, randomized, double-blind, placebo-controlled trial.

PATIENTS

  Fifty-three generally asymptomatic Fontan patients.

INTERVENTIONS

  Patients were randomized to receive either high-dose ascorbic acid (vitamin C) or placebo for 4 weeks.

OUTCOME MEASURES

  Peripheral vascular function, as measured with endothelium-dependent digital pulse amplitude testing (EndoPAT), and exercise capacity were assessed before and after study drug treatment. Primary outcome measures included the EndoPAT index and peripheral arterial tonometry (PAT) ratio, both validated markers of vascular function. Secondary outcome measures included peak oxygen consumption and work.

RESULTS

  Twenty-three vitamin C- and 21 placebo-assigned subjects completed the protocol (83%). Median age and time from Fontan completion were 15 (interquartile range [IQR] 11.7-18.2) and 11.9 years (IQR 9.0-15.7), respectively. Right ventricular morphology was dominant in 30 (57%). Outcome measures were similar between groups at baseline. Among all subjects, vitamin C therapy was not associated with a statistical improvement in either primary or secondary outcome measures. In subjects with abnormal vascular function at baseline, compared with placebo, vitamin C therapy more frequently resulted in normalization of the EndoPAT index (45% vs. 17%) and PAT ratio (38% vs. 13%).

CONCLUSIONS

  Short-term therapy with vitamin C does not alter endothelial function or exercise capacity in an asymptomatic Fontan population overall. Vitamin C may provide benefit to a subset of Fontan patients with abnormal vascular function.

Usefulness of peripheral vascular function to predict functional health status in patients with Fontan circulation

After the Fontan operation, patients are at a substantial risk of the development of impaired functional health status. Few early markers of suboptimal outcomes have been identified. We sought to assess the association between peripheral vascular function and functional health status in Fontan-palliated patients. Asymptomatic Fontan patients (n = 51) and age- and gender-matched healthy controls (n = 22) underwent endothelial pulse amplitude testing using a noninvasive fingertip peripheral arterial tonometry (PAT) device. Raw data were transformed into the PAT ratio, an established marker of vascular function. Cardiopulmonary exercise testing was performed using the Bruce protocol. In the Fontan cohort, 94% of patients were New York Heart Association functional class I and 88% had a B-type natriuretic peptide level of <50 pg/ml. The baseline pulse amplitude, a measure that reflects the arterial tone at rest, was greater in the Fontan patients than in the controls (median 2.74, interquartile range 1.96 to 4.13 vs median 1.86, interquartile range 1.14 to 2.79, p = 0.03). The PAT ratio, a measure of reactive hyperemia, was lower in Fontan patients (median 0.17, interquartile range -0.04 to 0.44, vs median 0.50, interquartile range 0.27 to 0.74, p = 0.002). The key parameters of exercise performance, including peak oxygen consumption (median 28.8 ml/kg/min, interquartile range 25.6 to 33.2 vs median 45.5 ml/kg/min, interquartile range 41.7 to 49.9, p <0.0001) and peak work (median 192 W, interquartile range 150 to 246 vs median 330, interquartile range 209 to 402 W, p <0.0001), were lower in Fontan patients than in the controls. The PAT ratio correlated with the peak oxygen consumption (r = 0.28, p = 0.02) and peak work (r = 0.26, p = 0.03). In conclusion, in an asymptomatic Fontan population, there is evidence of reduced basal peripheral arterial tone and vasodilator response, suggesting dysfunction of the endothelium-derived nitric oxide pathway. Vasodilator function appears to correlate with exercise performance.

Impact of spironolactone on endothelial function in patients with single ventricle heart

BACKGROUND

Mid-term survivors of the Fontan procedure are at risk for progressive heart failure, and endothelial dysfunction is thought to contribute to this process. Aldosterone antagonism has been shown to improve survival in adults with heart failure and the effects are mediated in part by changes in endothelial function. In the present study, we sought to determine if a short course of spironolactone improves endothelial function and alters serum cytokine profiles in adolescents and adults with single ventricle heart.

METHODS

Subjects had baseline assessment of flow-mediated dilation and cytokine profiles (C-reactive protein, interleukin-6, interleukin-1b, interleukin-10, tumor necrosis factor-alpha). They were started on spironolactone 25 mg once a day and uptitrated to 50 mg once daily. After 4 weeks, flow-mediated dilation and cytokine profiles were re-evaluated.

RESULTS

Ten subjects (median age 28 years) were enrolled and completed the protocol. The median flow-mediated dilation at baseline was 9.1% and did not change significantly after 4 weeks of spironolactone 7.6%, P = .46. There was mild elevation in serum cytokine profiles and only interleukin-1b decreased significantly with therapy, 0.39 to 0.23 pg/mL, P = .04.

CONCLUSIONS

In this small study, a short course of spironolactone did not improve endothelial function or alter the majority of serum cytokine levels. Whether single ventricle patients might realize other potential benefits of aldosterone antagonism such as reduced cardiac fibrosis remains to be determined.

Peripheral arterial function in infants and young children with one-ventricle physiology and hypoxemia

Patients with 1-ventricle (1V) physiology may be at risk for peripheral arterial dysfunction at a young age. To determine whether infants and young children with 1V physiology and hypoxemia have peripheral arterial dysfunction before undergoing the Fontan operation, we measured (1) flow-mediated vasodilation (FMD) in the brachial artery, (2) serum levels of vasoactive mediators endothelin-1 (ET-1) and metabolites of nitric oxide, and (3) arterial stiffness with pulse-wave velocity (PWV) in the aorta. Eighteen patients with 1V physiology before the Fontan procedure and hypoxemia and 19 patients with normoxemia and 2-ventricle (2V) physiology were studied. Measurements were collected during cardiac catheterization. FMD in the brachial artery was the diameter gain after 4.5 minutes of forearm occlusion measured with high-resolution ultrasound and edge-detection software. Nitric oxide and ET-1 levels were measured in venous blood. PWV between the left carotid and femoral arteries was measured using pulse Doppler ultrasound. FMD was lower (2.4 +/- 3.7% vs 11.3 +/- 6%, p <0.0005) and ET-1 levels were higher (35.5 +/- 11.3% vs 24.1 +/- 9.7%, p = 0.003) in subjects with 1V physiology versus those with 2V physiology, respectively. There were no differences in nitric oxide levels or PWV. In conclusion, infants and young children with 1V physiology and hypoxemia have blunted FMD and higher ET-1 levels before undergoing the Fontan operation compared with normoxemic subjects with 2V physiology. A further understanding of pathophysiologic mechanisms underlying peripheral arterial dysfunction, including the roles of hypoxemia, low cardiac index, and ET-1, may lead to targeted therapies and improve the long-term survival of patients with 1V physiology.

Protein-losing enteropathy after Fontan operation

Protein-losing enteropathy (PLE) is a poorly understood and enigmatic disease process affecting patients with single ventricle after Fontan operation. In those afflicted, PLE after Fontan operation results in significant morbidity and mortality. The pathophysiology of the disease is unknown; however, a proposed mechanism incorporates a combination of phenomena including: (1) altered hemodynamics, specifically low cardiac output; (2) increased mesenteric vascular resistance; (3) systemic inflammation; and (4) altered enterocyte basal membrane glycosaminoglycan make-up. A paradigm for the clinical management of PLE after Fontan operation is proposed.

Guidelines for the outpatient management of complex congenital heart disease

An increasingly complex group of children is now being followed as outpatients after surgery for congenital heart disease. A variety of complications and physiologic perturbations, both expected and unexpected, may present during follow-up, and should be anticipated by the practitioner and discussed with the patient and family. The purpose of this position article is to provide a framework for outpatient follow-up of complex congenital heart disease, based on a review of current literature and the experience of the authors.

Altered endothelial function following the Fontan procedure

OBJECTIVE

Thrombosis has been widely described after the Fontan procedure. The vascular endothelium plays a central role in the control of coagulation and fibrinolysis. The aim of this study was to investigate if patients undergoing a modified Fontan procedure have impaired endothelial function and fibrinolysis in the late postoperative course.

PATIENTS AND METHODS

We compared 23 patients aged from 7 to 26 years with age-matched healthy volunteers, collecting blood samples prior to and following standardized venous occlusion testing. Plasma levels of von Willebrand factor antigen, tissue-type plasminogen activator antigen, plasminogen activator inhibitor-1, and D-dimer were measured with enzyme-linked immunosorbent assay.

RESULTS

We found increased plasma levels of von Willebrand factor antigen in patients when compared to controls (p = 0.003). At the basal condition, concentrations of tissue-type plasminogen activator antigen and plasminogen activator inhibitor-1 antigen in the plasma, as well as their activity, were not significantly different between patients and controls. Following venous occlusion, concentrations of tissue-type plasminogen activator antigen in the plasma were significantly increased both in patients and controls, compared to pre-occlusion values. D-dimer was within the reference range. Multivariate discriminant analysis differentiated patients and their controls on the basis of differences for plasminogen activator inhibitor-1 and von Willebrand factor antigen (p = 0.0016).

CONCLUSIONS

Our data suggest that patients with the Fontan circulation may have endothelial dysfunction, as indicated by raised levels of von Willebrand factor. Fibrinolysis seems to be relatively preserved, as suggested by appropriate response to venous occlusion.

Impaired vascular function in patients with Fontan circulation

BACKGROUND

This study was performed to evaluate the endothelial function in Fontan patients, and to investigate the associated factors which influence the endothelial function in these patients.

METHODS

Flow mediated dilatation (FMD) and nitroglycerin induced dilatation (NG) of the brachial artery, and intima media thickness (IMT) of common carotid artery (CCA) were measured in nonselected Fontan patients (n=44, age 5 to 29 years, median 14 years, 18 females) by means of high-resolution ultrasound according to the standard protocols. The results were compared to age and sex matched controls (n=25, age 5 to 27 years, median 13 years, 10 females).

RESULTS

Fontan patients presented significantly reduced FMD and NG compared with controls (FMD; 6.5+/-2.4 vs. 11.1+/-1.4%, p<0.001, NG; 13.3+/-5.2 vs. 19.4+/-6.2%; p=0.035). Twenty two percent of Fontan patients presented pure endothelial dysfunction, and 34% of patients presented combined endothelial and smooth muscle dysfunction. Although there was no correlation between FMD and IMT, Fontan patients presented increased carotid IMT (0.44+/-0.07 vs. 0.38+/-0.06 mm, p=0.008). In multivariate analysis, duration of exposure to chronic hypoxia was inversely correlated with FMD (p=0.117, hazards ratio=1.294, 95% confidence interval=0.938-1.786). There was higher FMD in patients receiving angiotensin-converting enzyme inhibitors (ACEi) compared with those not receiving ACEi (7.0+/-2.5 vs. 5.5+/-2.2%, p=0.069).

CONCLUSIONS

Endothelial dysfunction is more prevalent in Fontan patients compared with healthy controls, and the previous hypoxia is an independent factor. Although it is not statistically significant, those patients on treatment with ACEi seem to have better endothelial function.

Oral Sildenafil Ameliorates Impaired Pulmonary Circulation Early After Bidirectional Cavopulmonary Shunt

We report a case of successful administration of oral sildenafil (ie, a phosphodiesterase-5 inhibitor) in an infant for impaired pulmonary circulation that caused early clinical deterioration after a bicavopulmonary shunt. The transpulmonary pressure gradient (ie, a clinical indicator of pulmonary circulation) was initially normalized by inhaled nitric oxide; however, an increase in transpulmonary pressure gradient and oxygen desaturation occurred after extubation and discontinuation of inhaled nitric oxide on postoperative day 1. Subsequent administration of oral sildenafil in stepwise doses resulted in normalization of transpulmonary pressure gradient and improved oxygen saturation with successful discontinuation of intravenous vasodilators. Our results suggest that oral sildenafil may be a potent adjunctive therapy for impaired postoperative pulmonary circulation after right heart bypass surgery.

Exercise Intolerance in Adults with Congenital Heart Disease

This article describes the ways to assess exercise capacity in adults with congenital heart disease (ACHD) and the impact of exercise intolerance in the population. It also discusses the likely pathogenesis of exercise intolerance in ACHD, the similarities between ACHD and acquired heart failure, and potential therapeutic options.

Protein-losing enteropathy after fontan operation: investigations into possible pathophysiologic mechanisms

BACKGROUND

Protein-losing enteropathy (PLE) is an enigmatic disease with significant morbidity and mortality seen after the Fontan operation. The pathophysiology is poorly understood. The purpose of this study is to investigate the association between PLE after the Fontan operation and candidate pathophysiologic mechanisms of the disease by searching for abnormalities of the following: (1) mesenteric blood flow; (2) systemic inflammation; (3) neurohormonal activation; (4) protein glycosylation.

METHODS

A cross-sectional analysis of 62 patients after the Fontan operation was performed. Twenty-four hour stool sample was collected for alpha-1-antitrypsin (A1AT) clearance, to determine the presence of abnormal enteric protein loss (AEPL) defined as either an abnormal fecal A1AT clearance of greater than 27 mL/24 hours, or an abnormal fecal A1AT concentration of greater than 54 mg/dL. Subjects underwent ultrasonography of the mesenteric and celiac artery blood flow and blood draw for tumor necrosis factor-alpha (TNF-a), high sensitivity C reactive protein (CRP), brain natriuretic peptide (BNP), angiotensin II, coagulation factors protein S, protein C, and antithrombin III (AT III), and serum transferrin for determination of glycosylation defect.

RESULTS

Age at study was 10.9 +/- 3.4 years; 8.6 +/- 3.9 years after the Fontan operation. Seven subjects had AEPL. Mesenteric-to-celiac artery flow ratio was lower for the AEPL group, than for the non-AEPL group (p < 0.05). The TNF-a, CRP, BNP, and angiotensin II levels were elevated; however, there was no correlation with AEPL. Abnormalities in coagulation factors were present but did not correlate with AEPL. No glycosylation defects were identified.

CONCLUSIONS

Potential candidate mechanisms for elucidation of the pathophysiology of PLE include abnormal mesenteric vascular resistance and inflammation, conditions uniquely present after the Fontan operation. Targeted investigations of these parameters may provide clues as to the mechanism of onset of PLE after Fontan operation.