What Limits Cardiac Performance during Exercise in Normal Subjects and in Healthy Fontan Patients?

Does High-Intensity Exercise Cause Acute Liver Injury in Patients with Fontan Circulation? A Prospective Pilot Study

The Fontan procedure results in chronic hepatic congestion and Fontan-associated liver disease (FALD) characterized by progressive liver fibrosis and cirrhosis. Exercise is recommended in this population, but may accelerate the progression of FALD from abrupt elevations in central venous pressure. The aim of this study was to assess if acute liver injury occurs after high-intensity exercise in patients with Fontan physiology. Ten patients were enrolled. Nine had normal systolic ventricular function and one had an ejection fraction < 40%. During cardiopulmonary exercise testing, patients had near-infrared spectroscopy (NIRS) to measure oxygen saturation of multiple organs, including the liver, and underwent pre- and post-exercise testing with liver elastography, laboratory markers, and cytokines to assess liver injury. The hepatic and renal NIRS showed a statistically significant decrease in oxygenation during exercise, and the hepatic NIRS had the slowest recovery compared to renal, cerebral, and peripheral muscle NIRS. A clinically significant increase in shear wave velocity occurred after exercise testing only in the one patient with systolic dysfunction. There was a statistically significant, albeit trivial, increase in ALT and GGT after exercise. Fibrogenic cytokines traditionally associated with FALD did not increase significantly in our cohort; however, pro-inflammatory cytokines that predispose to fibrogenesis did significantly rise during exercise. Although patients with Fontan circulation demonstrated a significant reduction in hepatic tissue oxygenation based on NIRS saturations during exercise, there was no clinical evidence of acute increase in liver congestion or acute liver injury following high-intensity exercise.

The utility of novel STE parameters in echocardiographic assessment of single ventricle after Fontan palliation

Background and aims of the study A functionally single ventricle (FSV) refers to a group of congenital heart defects that are not amenable for biventricular correction. The Fontan operation is utilized as surgical treatment for most of FSV patients. The evaluation of FSV function is extremely difficult due to its unique pathophysiology. This study aimed to explore the efficacy of speckle tracking echocardiography (STE) parameters measured at rest and during exercise for comprehensive assessment of univentricular heart.

METHODS

We enrolled 37 patients with a functionally single ventricle after the Fontan operation, hospitalized in the Department of Congenital Heart Defects between years 2019 and 2021.The echocardiographic stress tests were performed in the Echocardiography Laboratory of the Congenital Heart Defects Department. The study was conducted on a bicycle ergometer in a semi-recumbent position. The parameters obtained by speckle tracking echocardiography (STE): the longitudinal strain of the FSV free wall (Ɛ) and the longitudinal strain of myocardial layers: subendocardial, medial and subepicardial were analyzed. A transmural longitudinal strain gradient (TG) was calculated as the difference between longitudinal deformation of the subendocardial and subepicardial layers. Current results of cardiac magnetic resonance imaging (CMR) and cardio-pulmonary test (CPET) were also incorporated. Demographic data, past interventions, pharmacological treatment and comorbidities were extracted from medical records.

RESULTS

Ɛ at rest and during exercise were not related to the parameters of physical capacity obtained on CPET nor to the CMR results. The transmural strain gradient was dependent on physical performance parameter- peak oxygen uptake- and related to the FSV ejection fraction calculated by magnetic resonance imaging.

CONCLUSIONS

The transmural strain gradient and FSV free wall strain are readily measurable and suitable for evaluating single ventricle function. The TG is positively correlated with peak oxygen uptake during the cardiopulmonary test and with the ejection fraction derived from cardiac magnetic resonance imaging. The applicability of these findings in patients undergoing the Fontan procedure warrants further exploration.

A cavalpulmonary assist device utilising impedance pumping enhanced by peristaltic effect

BACKGROUND

Fontan procedure, the standard surgical palliation to treat children with single ventricular defects, causes systemic complications over years due to lack of pumping at cavopulmonary junction. A device developed specifically for cavopulmonary support is thus considered, while current commercial ventricular assist devices (VAD) induce high shear rates to blood, and have issues with paediatric suitability.

AIM

To demonstrate the feasibility of a small, valveless, non-invasive to blood and pulsatile rotary pump, which integrates impedance and peristaltic effects.

METHODS

A prototype pump was designed and fabricated in-house without any effort to optimise its specification. It was then tested in vitro, in terms of effect of pumping frequency, background pressure differences and pump size on output performance.

RESULTS

Net flow rate (NFR) and maximum pressure head delivery are both reasonably linearly dependent on pumping frequency within normal physiological range. Positive linearity is also observed between NFR and the extent of asymmetric pumping. The device regulates NFR in favourable pressure head difference and overcomes significant adverse pressure head difference. Additionally, performance is shown to be insensitive to device size.

CONCLUSIONS

The feasibility of the novel rotary pump integrating impedance and peristaltic effects is demonstrated to perform in normal physiological conditions without any optimisation effort. It provides promising results for possible future paediatric cavopulmonary support and warrants further investigation of miniaturisation and possible haemolysis.

Preoperative passive venous pressure-driven cardiac function determines left ventricular assist device outcomes

BACKGROUND

Right heart output in heart failure can be compensated through increasing systemic venous pressure. We determined whether the magnitude of this "passive cardiac output" can predict LVAD outcomes.

METHODS

This was a retrospective review of 383 patients who received a continuous-flow LVAD at the University of Michigan between 2012 and 2021. Pre-LVAD cardiac output driven by venous pressure was determined by dividing right atrial pressure by mean pulmonary artery pressure, multiplied by total cardiac output. Normalization to body surface area led to the passive cardiac index (PasCI). The Youden J statistic was used to identify the PasCI threshold, which predicted LVAD death by 2 years.

RESULTS

Increased preoperative PasCI was associated with reduced survival (hazard ratio [HR], 2.27; P < .01), and increased risk of right ventricular failure (RVF) (HR, 3.46; P = .04). Youden analysis showed that a preoperative PasCI ≥0.5 (n = 226) predicted LVAD death (P = .10). Patients with PasCI ≥0.5 had poorer survival (P = .02), with a trend toward more heart failure readmission days (mean, 45.09 ± 67.64 vs 35.13 ± 45.02 days; P = .084) and increased gastrointestinal bleeding (29.2% vs 20.4%; P = .052). Additionally, of the 97 patients who experienced readmissions for heart failure, those with pre-LVAD implantation PasCI ≥0.5 were more likely to have more than 1 readmission (P = .05).

CONCLUSIONS

Although right heart output can be augmented by raising venous pressure, this negatively impacts end-organ function and increases heart failure readmission days. Patients with a pre-LVAD PasCI ≥0.5 have worse post-LVAD survival and increased RVF. Using the PasCI metric in isolation or incorporated into a predictive model may improve the management of LVAD candidates with RV dysfunction.

Cardiovascular Imaging-Derived Skeletal Muscle Mass Correlates With Fitness and Survival in Patients With Univentricular Circulation

Aims This study aims to retrospectively quantify skeletal muscle mass from cardiovascular imaging studies in total cavopulmonary connection (TCPC) patients and to correlate calculated muscle mass with clinical outcomes. Materials and methods Ninety-one TCPC patients at a mean age of 24.0 ±5.5 years (37 women; 40.7%) who underwent chest computed tomography (CT) or cardiac magnetic resonance imaging (MRI) as part of their follow-up were identified in a single-center database. The cross-sectional skeletal muscle index (SMI) at the Th4 and Th12 levels was calculated from CT images, and the dorsal skeletal muscle area (SMA) at the Th12 level was measured from an MRI. Results Calculated SMI at Th12 level was 38.0 (34.5; 42.0) cm2.m-2 or 89.6 (81.9; 101.6) % of predicted values. The median follow-up from CT was 5.9 (3.1; 8.5) years, and the composite endpoint (death N=5, heart transplant N=6) was reached in a total of 11 (26.8%) patients. Patients with SMI (Th12) less than 90% of predicted values had a hazard ratio of 5.8 (95% CI: 1.2; 28.3) (p=0.03) for endpoint achievement. In the MRI group, dorsal SMA at the Th12 level was 27.6 ±5.1 cm2 in men and 20.0 ±5.8 cm2 in women. Correlations were found between SMA/kg and peak oxygen uptake (VO2 peak) (r=0.48, p=0.0005) and fat-free mass (r=0.63, p<0.0001), respectively. Conclusions A low SMI at the Th12 level was associated with a higher risk of death or cardiac transplantation. Evaluation of skeletal muscle mass using cardiovascular imaging methods allows rapid identification of individuals at risk of sarcopenia.

Home-Based Resistance Training Programme in Fontan Patients: It Is Feasible, Safe, and Efficient

Background

Fontan physiology is characterized by a single functional systemic ventricle that reduces cardiac output adaptation and exercise capacity. Peripheral muscle pump is crucial for venous return, and resistance training of the peripheral muscles may be particularly beneficial for cardiac function in these patients. This study explores the feasibility of a training programme including safety and effectiveness, maximal exercise capacity, cardiorespiratory endurance, and quality of life in a Fontan population.

Methods

Twelve Fontan patients (18-32 years old) with New York Heart Association functional classes I and II were recruited. The intervention was 12 weeks of home-based exercise programme of 3 sessions per week supervised online by a physiotherapist. Pre- and postintervention evaluations assessed lean body mass, segmental forces with a hand-held dynamometer, maximal oxygen consumption (VO2max), cardiovascular endurance, leg endurance with a 1-minute-sit-to-stand test, and quality of life with a 36-item Short-Form Survey.

Results

A total of 11 of 12 participants completed 35 of 36 workouts, exceeding our 80% threshold for completion. No adverse events were reported. Leg muscle strength increased significantly (knee extensors improved by 22.8 ± 22.8 N m [17.7%], P = 0.019). Despite no change in VO2max, endurance time showed a significant improvement of 5.3 minutes (72%). Perceived physical condition evaluated with a self-perception scale improved significantly. There was no significant difference in the lean body mass and in quality of life.

Conclusion

In this small group of post-Fontan patients with mild functional impairments, we describe a structured, accessible, and feasible home-based resistance training programme that seems safe and show improvements in strength and perceived physical condition.

Exercise Pathophysiology and Testing in Individuals With a Fontan Circulation

The Fontan circulation, a surgical palliation for single-ventricle congenital heart disease, profoundly impacts the cardiopulmonary response to exercise. Reliant on passive pulmonary blood flow, the Fontan circulation has limited capacity to augment cardiac output as necessary to supply working muscles during exercise. Cardiopulmonary exercise testing (CPET) objectively assesses cardiorespiratory fitness and provides insight into the etiology of exercise intolerance. Furthermore, CPET variables, such as peak oxygen consumption and submaximal variables, have prognostic value and may be used as meaningful endpoints in research studies. CPET is also useful in clinical research applications to assess the effect of pharmacologic or other interventions. Medical therapies to improve exercise tolerance in individuals with a Fontan circulation, such as pulmonary vasodilators, may modestly improve peak oxygen consumption. Exercise training focused on aerobic fitness and lower extremity strength may have a more consistent and larger impact on these measures of aerobic fitness. CPET is a valuable diagnostic and prognostic tool for those with a Fontan circulation. Newer ancillary assessments, such as noninvasive peripheral venous pressure monitoring and cardiac output measurements, hold promise to provide a more nuanced insight into the underlying pathophysiology.

Orthostatic stress response in pediatric Fontan patients and the effect of ACE inhibition

Background

Many cardiocirculatory mechanisms are involved in the adaptation to orthostatic stress. While these mechanisms may be impaired in Fontan patients. However, it is yet unclear how Fontan patients, who exhibit a critical fluid balance, respond to orthostatic stress. Angiotensin converting enzyme inhibitors are often prescribed to Fontan patients, but they may negatively influence orthostatic tolerance. Therefore, we evaluated the response to orthostatic stress in pediatric Fontan patients before and after treatment with enalapril.

Methods

Thirty-five Fontan patients (aged 14 years) with moderate-good systolic ventricular function without pre-existent enalapril treatment were included. Before and after a three-month enalapril treatment period, the hemodynamic response to head-up tilt test was evaluated by various parameters including cardiac index, blood pressure, cerebral blood flow, aortic stiffness and cardiac autonomous nervous activity. Thirty-four healthy subjects (aged 13 years) served as controls.

Results

Fontan patients had a decreased cerebral blood flow and increased aortic stiffness in the supine position compared to controls, while all other factors did not differ. Patients and controls showed a comparable response to head-up tilt test for most parameters. Twenty-seven patients completed the enalapril study with a mean dosage of 0.3±0.1mg/kg/day. Most parameters were unaffected by enalapril, only the percent decrease in cardiac index to tilt was higher after treatment, but the cardiac index during tilt was not lower (3.0L/min/m2 pre-enalapril versus 2.8L/min/m2 after treatment; P = 0.15).

Conclusion

Pediatric Fontan patients adequately respond to orthostasis with maintenance of blood pressure and cerebral blood flow and sufficient autonomic response. Enalapril treatment did not alter the response.

Clinical trial information

Scientific title: ACE inhibition in Fontan patients: its effect on body fluid regulation (sAFE-study).

The Netherlands National Trial Register: Trail NL6415. Registered 2017-07-20.

Trial information: https://www.trialregister.nl/trial/6415

Exercising with a Single Ventricle: Limitations and Therapies

Treatment for Hypoplastic Left Heart Syndrome (HLHS) and other single ventricle conditions requires a series of surgical interventions for long-term survival, typically culminating in the Fontan procedure. The result is an abnormal circulatory physiology with an absence of a sub-pulmonary ventricle. Exercise capacity in the Fontan circulation is often limited and is due to multiple factors, both central and peripheral. Multiple interventions, both pharmacologic and nonpharmacologic, have been studied to attempt to overcome these inherent limitations. This review will focus on the physiology of the exercising Fontan patient and on the interventions aimed at the enhancement of exercise capacity studied thus far.

Exercise Training for People Living with a Fontan Circulation: An Underutilized Intervention

Surgical repair for children born with single ventricle congenital heart disease, culminating in the Fontan operation, has resulted in dramatic improvements in survival; children born with these lesions are now typically expected to survive well into adulthood. Most, but not all, individuals with a Fontan circulation have reduced exercise capacity compared with the general population that in turn is associated with increased cardiovascular morbidity and mortality. The cause of reduced exercise capacity is multifactorial. A significant contributor is the absence of a subpulmonary ventricular pump, which limits preload and appropriate cardiac output augmentation to meet the increased metabolic demands that occur with exercise. While in its infancy relative to adults with acquired heart disease, the evidence to date suggests that exercise interventions to improve exercise capacity and Fontan physiology in children and adults with Fontan circulation are safe, effective and well tolerated. However, many knowledge gaps remain, including a detailed understanding of the unique physiological adaptations that occur, the optimal approach to exercise in this population and the effectiveness of home-based interventions utilizing telemedicine and remote physiologic monitoring technologies. Furthermore, the long-term impact of such interventions on the Fontan-cardiovascular system, physical activity levels, health-related quality of life, and late cardiovascular morbidity and mortality are not well characterized. In this review, we outline the factors associated with reduced exercise capacity in individuals with Fontan circulation, review the experience to date of dedicated interventions to improve exercise capacity, and highlight the current knowledge gaps in the field and priorities for further study.

Exercise Prescription Enhances Maximal Oxygen Uptake and Anaerobic Threshold in Young Single Ventricle Patients with Fontan Circulation

A modified Fontan procedure is performed to palliate single ventricle malformations. This hemodynamic arrangement sets systemic venous pressure unphysiologically high which predisposes the patient to severe long-term complications. As a means of self-care, exercise may ease transpulmonary flow. We investigated the effects of 6-month exercise prescription on pediatric Fontan patients. Eighteen stable Fontan patients (14 ± 2.6 years, 160.4 ± 11.3 cm, and 51.4 ± 14.4 kg) were recruited. Baseline fitness was assessed by physical activity questionnaire, body composition, cardiorespiratory performance, and muscle fitness tests. Exercise prescription was individually tailored for a 6-month training period at home. At entrance to the study, Fontan patients had lower than normal maximal oxygen uptake (VO_2max) of 28. ± 5.9 ml/kg/min (61 ± 11% of normal). VO_2max significantly correlated with weekly amount of habitual exercise and muscle mass of the lower limbs (p < 0.001 for both). After 6 months of training, the patients had improved their anaerobic threshold of 18 ± 3.5 vs 20 ± 4.8 ml/kg/min, p = 0.007, and workload tolerance of 119 ± 39 vs 132.4 ± 44 W, p = 0.001. At EUROFIT tests, the patient muscle fitness was below age-matched reference, but correlations existed between VO_2max and lower limb muscle tests. Our patients with Fontan hemodynamics were able to positively respond to an exercise program by enhancing submaximal performance which should be beneficial for getting through daily activities. Future studies should correlate whether hemodynamic findings at Fontan completion influence physical activity and exercise reserves, and whether these predict predisposition to chronic complications.

Adequate exercise response at artificial altitude in Fontan patients

PURPOSE

For Fontan-palliated patients, altitude exposure is still a part of discussion since the extent of hypoxic pulmonary vasoconstriction potentially resulting in decreasing cardiac output (Qc), especially during physical exercise, is still unclear. We investigated the effects of normobaric hypoxia (15.2% O₂) simulating 2,500 m above sea level on cardiopulmonary and metabolic parameters and the benefit of daily physical activity (PA) on hypoxic exercise capacity.

METHODS

A total of 21 Fontan patients (14-31 years) and 20 healthy controls performed cardiopulmonary exercise tests on a bicycle ergometer in normoxia and hypoxia until subjective exhaustion, measuring capillary lactate (cLa) every 2 min. In between, participants underwent an activity tracking over 5 days with a triaxial accelerometer.

RESULTS

Hypoxic exercise was well tolerated by Fontan patients, and no adverse clinical events were observed. Fontan patients showed reduced physical capacity under both conditions compared to controls (63% normoxia, 62% hypoxia), but the relative impairment due to hypoxia was similar for both (≈10%). Up to workloads of 2 W/kg oxygen uptake ( V . O₂) and heart rate (HR) developed similarly in patients and controls. cLa increased faster in relation to workload in Fontan patients, but remained significantly lower at peak workload (normoxia 3.88 ± 1.19 mmol/l vs. 7.05 ± 2.1 mmol/l; hypoxia 4.01 ± 1.12 mmol/l vs. 7.56 ± 1.82 mmol/l). Qc was diminished but could be increased similar to controls. Fontan patients with higher PA levels showed a higher V . O_2peak in hypoxia.

CONCLUSION

Exercise during short-time artificial altitude exposure seems to be safe for young Fontan patients. Further studies are needed to validate longer exposure under real conditions. V . O₂, HR, and Qc might not be a limiting factor for exercise until workloads of 2 W/kg. Higher daily PA levels might improve physical capacity under altitude conditions.

Impairments in Pulmonary Function in Fontan Patients: Their Causes and Consequences

Patients with a Fontan circulation lack a sub-pulmonary ventricle with pulmonary blood flow passively redirected to the lungs. In the Fontan circulation, ventilation has a significant influence on pulmonary blood flow and cardiac output both at rest and with exercise. Children and adults with a Fontan circulation have abnormalities in lung function. In particular, restrictive ventilatory patterns, as measured by spirometry, and impaired gas transfer, as measured by the diffusing capacity of carbon monoxide, have been frequently observed. These abnormalities in lung function are associated with reduced exercise capacity and quality of life. Moderate to severe impairment in lung volumes is independently associated with reduced survival in adults with congenital heart disease. Skeletal and inspiratory muscle weakness has also been reported in patients with a Fontan circulation, with the prospect of improving respiratory muscle function through exercise training programs. In this review, we will present data on cardiopulmonary interactions in the Fontan circulation, the prevalence and severity of impaired lung function, and respiratory muscle function in this population. We will discuss potential causes for and consequence of respiratory impairments, and their impact on exercise capacity and longer-term Fontan outcome. We aim to shed light on possible strategies to reduce morbidity by improving respiratory function in this growing population of patients.

Exercise-Induced Cardiac Troponin Elevations: From Underlying Mechanisms to Clinical Relevance

Supplemental Digital Content is available in the text.

Serological assessment of cardiac troponins (cTn) is the gold standard to assess myocardial injury in clinical practice. A greater magnitude of acutely or chronically elevated cTn concentrations is associated with lower event-free survival in patients and the general population. Exercise training is known to improve cardiovascular function and promote longevity, but exercise can produce an acute rise in cTn concentrations, which may exceed the upper reference limit in a substantial number of individuals. Whether exercise-induced cTn elevations are attributable to a physiological or pathological response and if they are clinically relevant has been debated for decades. Thus far, exercise-induced cTn elevations have been viewed as the only benign form of cTn elevations. However, recent studies report intriguing findings that shed new light on the underlying mechanisms and clinical relevance of exercise-induced cTn elevations. We will review the biochemical characteristics of cTn assays, key factors determining the magnitude of postexercise cTn concentrations, the release kinetics, underlying mechanisms causing and contributing to exercise-induced cTn release, and the clinical relevance of exercise-induced cTn elevations. We will also explain the association with cardiac function, correlates with (subclinical) cardiovascular diseases and exercise-induced cTn elevations predictive value for future cardiovascular events. Last, we will provide recommendations for interpretation of these findings and provide direction for future research in this field.

Exercise capacity after total cavopulmonary anastomosis: a longitudinal paediatric and adult study

AIMS

Fontan palliation is a surgical strategy for patients with complex congenital heart disease, in whom biventricular circulation cannot be achieved. Long-term survival is negatively affected by the absence of sub-pulmonary ventricle and increased systemic venous pressure. Exercise capacity is a known predictor of overall survival and quality of life in congenital heart defects. We aim to track individual trends of peak oxygen uptake (V̇O₂ peak) after total cavopulmonary connection (TCPC), identify predictors of deterioration, and derive a disease-specific reference V̇O₂ peak dataset.

METHODS AND RESULTS

A retrospective study of serial cardiopulmonary exercise testing (CPET) data, gathered from all patients who underwent TCPC in the Czech Republic between 1992 and 2016. Of 354 consecutive patients with TCPC, 288 (81.4%) patients underwent one or more CPETs yielding 786 unique V̇O₂ peak values used as a reference dataset. Longitudinal data were available in 206 (58.2%) patients, who underwent a median (inter-quartile range) of 3.0 (2.0-5.0) CPETs over a mean (standard deviation) of 8.9 (5.5) years. The decline of exercise capacity with age was linear and not faster than in healthy peers (P = 0.47), but relative values of V̇O₂ peak in TCPC patients were 12.6 mL/min/kg lower. Single ventricular morphology and pulmonary artery size had no significant influence on the exercise capacity dynamics. V̇O₂ peak decline correlated negatively with the trend of body mass index z-score (P = 0.006) and was faster in women than men (P = 0.008).

CONCLUSIONS

Total cavopulmonary connection patients have significantly reduced exercise capacity. The age-related decline paralleled the healthy population and correlated negatively with the body mass index trend. The presented V̇O₂ peak reference dataset may help the clinicians to grade the severity of exercise capacity impairment in individual TCPC patients.

Predictors of Poor Functional Status in Adult Fontan Patients Living at Moderate Altitude

Patients who have undergone Fontan palliation have reduced exercise tolerance measured by maximal oxygen consumption (VO₂ max). Declining exercise capacity is associated with increased morbidity and mortality. The impact of hemodynamics and other variables on this population's functional status is not well understood. This study sought to identify variables that predict low VO₂ max in Fontan patients living at moderate altitude (5,000-8,000 feet). We performed a retrospective cohort study of 44 adult Fontan patients living at moderate altitude who had undergone cardiopulmonary exercise testing (CPET) and cardiac catheterization. We evaluated hemodynamic parameters measured during catheterization, imaging results, and laboratory studies for correlation with VO₂ max measured during CPET. Our study cohort (median age 30 years, 52% female) had exercise impairment with mean VO₂ max of 21.6 mL/kg/min. Higher trans-pulmonary gradient (TPG) (p < 0.001) and mean pulmonary artery (PA) pressure (p = 0.013) were predictors of lower maximal and submaximal VO₂. Higher BNP values correlated with lower VO₂ max (p = 0.01). Platelet count, GGT, albumin, and pulmonary vasodilator therapy did not correlate with VO₂ max. None of the studied variables were associated with higher minute ventilation to peak carbon dioxide production (VE/VCO₂ slope) or change in VO₂ max over time. In conclusion, higher TPG and mean PA pressure predicted lower exercise tolerance amongst our cohort of adult Fontan patients living at moderate altitude. Future studies are needed to determine if these clinical variables represent viable therapeutic targets that could result in improved exercise tolerance and outcomes in patients with Fontan circulation.

Angiotensin-converting enzyme inhibition and pre-superior cavopulmonary connection haemodynamics in infants with single-ventricle physiology

INTRODUCTION

Preliminary animal and human data suggest that angiotensin-converting enzyme inhibition has a role in pulmonary vascular remodelling. We sought to assess the effect of ACEi versus placebo on pulmonary artery pressure and transpulmonary gradient amongst infants undergoing single-ventricle palliation.

MATERIALS AND METHODS

Using the publicly available Pediatric Heart Network Infant Single-Ventricle trial dataset, we compared mean PA pressure at pre-superior cavopulmonary connection catheterisation (primary outcome), transpulmonary gradient, pulmonary-to-systemic flow ratio, and post-SCPC oxygen saturation (secondary outcomes) in infants receiving enalapril versus placebo.

RESULTS

A total of 179 infants underwent pre-SCPC catheterisation, of which 85 (47%) received enalapril. There was no difference between the enalapril and placebo group in the primary and the secondary outcomes. Mean PA pressure in the enalapril group was 13.1 ± 2.9 compared to 13.7 ± 3.4 mmHg in the placebo group. The transpulmonary gradient was 6.7 ± 2.5 versus 6.9 ± 3.2 mmHg in the enalapril and placebo groups, respectively. The pulmonary-to-systemic flow ratio was 1.1 ± 0.5 in the enalapril group versus 1.0 ± 0.5 in the placebo group and the post-SCPC saturation was 83.1 ± 5.0% in the enalapril group versus 82.2 ± 5.3% in the placebo group. In the pre-specified subgroup analyses comparing enalapril and placebo according to ventricular morphology and shunt type, there was no difference in the primary and secondary outcomes.

CONCLUSION

ACEi did not impact mean pulmonary artery pressure or transpulmonary gradient amongst infants with single-ventricle physiology prior to SCPC palliation.

Dynamic exercise changes in venous pressure and liver stiffness in Fontan patients: effects of Treprostinil

BACKGROUND

Systemic venous hypertension and low cardiac output are believed to be important mediators of liver injury after the Fontan procedure. Pulmonary vasodilators have the potential to improve such haemodynamics. The aim of this study was to assess the acute effects of exercise on liver stiffness and venous pressures and to assess the impact of inhaled Treprostinil on this response.

METHODS

In this prospective, double-blind, placebo-controlled, crossover trial, 14 patients with a Fontan circulation were randomised to inhalation of placebo and Treprostinil. Incremental and constant work rate exercise tests were performed to assess the effect of Treprostinil on exercise tolerance. Venous pressures were measured throughout and liver stiffness at rest and immediately after peak exercise.

RESULTS

Mean age was 27.8 ± 7.9 years and 66% were females. Exercise acutely increased liver stiffness by 30% (mean shear wave speed: 2.38 ± 0.71 versus 2.89 ± 0.51 ms, p = 0.02). Peripheral venous pressures increased acutely during both incremental (12.1 ± 2.4 versus 22.6 ± 8.0 mmHg, p < 0.001) and constant work rate exercise (12.5 ± 2.5 versus 23.4 ± 5.2 mmHg, p < 0.001). Overall, Treprostinil failed to attenuate exercise-induced increases in liver stiffness. Compared with placebo, Treprostinil did not significantly impact venous pressure responses, VO2peak, nor exercise endurance times.

CONCLUSIONS

Peripheral venous pressure increased acutely during exercise by an average of 88% above baseline and was not altered by administration of inhaled Treprostinil. Liver stiffness measured immediately post-exercise increased acutely by an average of 30%, with no attenuation following Treprostinil inhalation.

Pregnancy in the FONTAN palliation: physiology, management and new insights from bioengineering

Fontan palliation for the single ventricle results in a challenging and delicate physiological state. At rest, the body adapts to a low cardiac output and high systemic venous pressure. However, when physiological demands increase, such as in the case of exercise or pregnancy, this delicate physiology struggles to adapt due to the inability of the heart to pump blood into the lungs and the consequent lack of augmentation of the cardiac output.

Due to the advances in paediatric cardiology, surgery and intensive care, today most patients born with congenital heart disease reach adulthood. Consequently, many women with a Fontan circulation are becoming pregnant and so far data suggest that, although maternal risk is not high, the outcomes are poor for the foetus. Little is known about the reasons for this disparity and how the Fontan circulation adapts to the physiological demands of pregnancy.

Here we review current knowledge about pregnancy in Fontan patients and explore the potential role of computational modelling as a means of better understanding this complex physiology in order to potentially improve outcomes, particularly for the foetus.

Ventricular myocardial response to exercise in patients with Fontan circulation

BACKGROUND

Exercise stress echocardiography has been used to assess myocardial reserve in various heart diseases. This study examined the ventricular myocardial response to exercise in Fontan patients using exercise stress echocardiography.

METHODS

Twenty-five Fontan patients and 19 control subjects underwent semi-supine bicycle exercise stress echocardiography in this prospective, single-center, cross-sectional study. Pulsed-wave Doppler tissue imaging peak systolic (s') and diastolic (e') velocities, longitudinal strain and systolic strain rate, and early diastolic strain rate data at rest and at peak exercise were obtained for the systemic ventricle. The myocardial reserve of functional parameters was calculated as the difference between peak exercise and rest.

RESULTS

Inter- and intra-observer reliability were both high for exercise stress echocardiography measurements. Compared with controls, Fontan patients had significantly lower s', e', longitudinal systolic strain and strain rate, and early diastolic longitudinal strain rate at rest and at peak exercise as well as reduced myocardial reserve.

CONCLUSIONS

Fontan patients have markedly reduced myocardial reserve during exercise. The use of exercise stress echocardiography assessment may improve the clinical management of Fontan patients.

Exercise Intolerance, Benefits, and Prescription for People Living With a Fontan Circulation: The Fontan Fitness Intervention Trial (F-FIT)-Rationale and Design

Background: Despite developments in surgical techniques and medical care, people with a Fontan circulation still experience long-term complications; non-invasive therapies to optimize the circulation have not been established. Exercise intolerance affects the majority of the population and is associated with worse prognosis. Historically, people living with a Fontan circulation were advised to avoid physical activity, but a small number of heterogenous, predominantly uncontrolled studies have shown that exercise training is safe-and for unique reasons, may even be of heightened importance in the setting of Fontan physiology. The mechanisms underlying improvements in aerobic exercise capacity and the effects of exercise training on circulatory and end-organ function remain incompletely understood. Furthermore, the optimal methods of exercise prescription are poorly characterized. This highlights the need for large, well-designed, multi-center, randomized, controlled trials. Aims and Methods: The Fontan Fitness Intervention Trial (F-FIT)-a phase III clinical trial-aims to optimize exercise prescription and delivery in people with a Fontan circulation. In this multi-center, randomized, controlled study, eligible Fontan participants will be randomized to either a 4-month supervised aerobic and resistance exercise training program of moderate-to-vigorous intensity followed by an 8-month maintenance phase; or usual care (control group). Adolescent and adult (≥16 years) Fontan participants will be randomized to either traditional face-to-face exercise training, telehealth exercise training, or usual care in a three-arm trial with an allocation of 2:2:1 (traditional:telehealth:control). Children (<16 years) will be randomized to either a physical activity and exercise program of moderate-to-vigorous intensity or usual care in a two-arm trial with a 1:1 allocation. The primary outcome is a change in aerobic exercise capacity (peak oxygen uptake) at 4-months. Secondary outcomes include safety, and changes in cardiopulmonary exercise testing measures, peripheral venous pressure, respiratory muscle and lung function, body composition, liver stiffness, neuropsychological and neurocognitive function, physical activity levels, dietary and nutritional status, vascular function, neurohormonal activation, metabolites, cardiac function, quality of life, musculoskeletal fitness, and health care utilization. Outcome measures will be assessed at baseline, 4-months, and 12-months. This manuscript will describe the pathophysiology of exercise intolerance in the Fontan circulation and the rationale and protocol for the F-FIT.

Appropriate heart rate during exercise in Fontan patients

OBJECTIVE

To evaluate heart rate against workload and oxygen consumption during exercise in Fontan patients.

METHOD

Fontan patients (n = 27) and healthy controls (n = 25) underwent cardiopulmonary exercise testing with linear increase of load. Heart rate and oxygen uptake were measured during tests. Heart rate recovery was recorded for 10 minutes.

RESULTS

Heart rate at midpoint (140 ± 14 versus 153 ± 11, p < 0.001) and at maximal effort (171 ± 14 versus 191 ± 10 beats per minute, p < 0.001) of test was lower for patients than controls. Heart rate recovery was similar between groups. Heart rate in relation to workload was higher for patients than controls both at midpoint and maximal effort. Heart rate in relation to oxygen uptake was similar between groups throughout test. Oxygen pulse, an indirect surrogate measure of stroke volume, was reduced at maximal effort in patients compared to controls (6.6 ± 1.1 versus 7.5 ± 1.4 ml·beat-1·m-2, p < 0.05) and increased significantly less from midpoint to maximal effort for patients than controls (p < 0.05).

CONCLUSIONS

Heart rate is increased in relation to workload in Fontan patients compared with controls. At higher loads, Fontan patients seem to have reduced heart rate and smaller increase in oxygen pulse, which may be explained by inability to further increase stroke volume and cardiac output. Reduced ability to increase or maintain stroke volume at higher heart rates may be an important limiting factor for maximal cardiac output, oxygen uptake, and physical performance.

Effect of sympathetic autonomic stress from the cold pressor test on left ventricular function in young healthy adults

There is a dearth of studies investigating the effect of sympathetic activation on left ventricular function. This study aimed to investigate the effect of sympathetic autonomic stress on left ventricular function in young healthy adults. Fifty‐six normotensive healthy participants (age 23.55 ± 3.82 years) took part in the study after giving informed consent. After obtaining baseline measurements, heart rate (HR), blood pressure (BP), peripheral saturation of oxygen (SpO2) and left ventricular function (assessed by means of ejection fraction (EF) obtained by transthoracic 2‐D echocardiography) were determined before and following sympathetic activation using cold pressor test (CPT). Exposure to CPT led to significant increase (P < 0.0001) in HR (70.4 ± 10.7 bpm to 91.6 ± 14.8 bpm), SBP (118 ± 8 mmHg to 138 ± 14 mmHg) and DBP (71 ± 7 mmHg to 91 ± 11 mmHg). Participants’ EDV (101.1 ± 15.8 ml to 104.2 ± 19.3 mL), ESV (38.7 ± 9.1 mL to 40.3 ± 11.6 mL), SpO2 (99.5 ± 0.79% to 99.5 ± 0.77%) and EF (61.9 ± 5.9% to 60.9 ± 6.4%) were only slightly changed (P > 0.05). However, cardiac output (4.3 ± 0.9 L/min to 5.4 ± 1.4 L/min) and cardiac index (3.7 ± 0.8 L/min per m² to 4.5 ± 1.4 L/min per m²) increased significantly (P < 0.0001). We conclude that sympathetic stress induced by cold pressor test has marginal effect on ejection fraction and fractional shortening while increasing cardiac output and cardiac index in young healthy adults.

Pulmonary vasodilator therapy after the Fontan procedure: a meta-analysis

We aimed to assess the efficacy and safety of pulmonary vasodilators in patients after the Fontan procedure. The PubMed, EMBASE, and Cochrane Library databases were searched through November 2019 for studies comparing pulmonary vasodilators and controls in Fontan patients. The variables assessed included change in pulmonary resistance, heart function, exercise capacity, quality of life, mortality, and adverse events after drug administration. A random/fixed effects model was used to assess the mean difference (MD)/risk ratio (RR) with 95% confidence intervals (CIs). Subgroup analysis was stratified by drug category. In total, 449 Fontan patients from 13 studies were included. Pooled estimates of the change in pulmonary arterial pressure (MD, - 1.07; 95% CI, - 2.75 to 0.60; p = 0.21), New York Heart Association class (MD, - 0.57; 95% CI, - 1.41 to 0.28; p = 0.19), peak oxygen consumption (MD, 1.46; 95% CI, 0.01 to 2.90; p = 0.05), Short Form 36 (MD, 1.39; 95% CI, - 0.62 to 3.39; p = 0.17), mortality (RR, 0.37; 95% CI, 0.08 to 1.65; p = 0.19), and any adverse event (RR, 0.94; 95% CI, 0.71 to 1.24; p = 0.64) were not significantly different between the drug and control groups. Likewise, most results of the subgroup analysis revealed no significant between-group differences. Pulmonary vasodilator therapy appears to be safe, but not beneficial, in the categories of pulmonary resistance, heart function, or quality of life in patients who have undergone a Fontan procedure. No significant evidence was found to confirm that most pulmonary vasodilators could improve exercise capacity in Fontan patients.

Differences in cerebral and muscle oxygenation patterns during exercise in children with univentricular heart after Fontan operation compared to healthy peers

BACKGROUND

We assess whether the lower exercise tolerance in children with univentricular heart (UVH) after Fontan operation is associated with altered peripheral muscular and cerebral tissue oxygenation.

METHODS

18 children with UVH and 20 healthy subjects performed an incremental ramp exercise test. Changes in the cerebral and muscular pattern of oxygenated (O₂Hb) and deoxygenated hemoglobin (HHb) and local tissue oxygenation (TOI) were analyzed by means of Near Infrared Spectroscopy (NIRS). Correlations between arterial saturation during exercise and tissue oxygenation were evaluated.

RESULTS

In UVH, maximal oxygen consumption (VO₂peak/kg, 28.9 ± 7.9 vs. 46.3 ± 11.9 ml/min/kg, P < 0.001), heart rate (HRpeak, 168 ± 13 vs. 193 ± 12 bpm, P < 0.001) and load (Ppeak, 73 ± 19 vs. 133 ± 68 W, P < 0.001) were lower, VE/VCO₂ slope was higher (34.5 ± 5.9 vs. 27.1 ± 3.9, P < 0.001). A faster and steeper course up to the same level of HHb and absent increase in O₂Hb was seen at cerebral level in UVH; tissue oxygenation index (TOI) demonstrated a steady decrease from the start of exercise. At the muscular level, HHb curve has a similar pattern compared to controls, with an early cessation. O₂Hb has a similar pattern, but with early discontinuation at a higher O₂Hb-level. Muscular TOI has the same course throughout exercise, starting from a lower level. Lower arterial saturation and higher age correlated with lower VO₂peak; higher amplitude of muscular TOI and lower amplitude cerebral TOI correlated with higher VO₂peak.

CONCLUSION

Children after Fontan procedure have different oxygenation mechanisms at muscular and cerebral level. This reflects a different balance between O₂ supply to O₂ demand which might contribute to the reduced exercise tolerance in this patient population.

Evaluation and Management of the Child and Adult With Fontan Circulation: A Scientific Statement From the American Heart Association

It has been 50 years since Francis Fontan pioneered the operation that today bears his name. Initially designed for patients with tricuspid atresia, this procedure is now offered for a vast array of congenital cardiac lesions when a circulation with 2 ventricles cannot be achieved. As a result of technical advances and improvements in patient selection and perioperative management, survival has steadily increased, and it is estimated that patients operated on today may hope for a 30-year survival of >80%. Up to 70 000 patients may be alive worldwide today with Fontan circulation, and this population is expected to double in the next 20 years. In the absence of a subpulmonary ventricle, Fontan circulation is characterized by chronically elevated systemic venous pressures and decreased cardiac output. The addition of this acquired abnormal circulation to innate abnormalities associated with single-ventricle congenital heart disease exposes these patients to a variety of complications. Circulatory failure, ventricular dysfunction, atrioventricular valve regurgitation, arrhythmia, protein-losing enteropathy, and plastic bronchitis are potential complications of the Fontan circulation. Abnormalities in body composition, bone structure, and growth have been detected. Liver fibrosis and renal dysfunction are common and may progress over time. Cognitive, neuropsychological, and behavioral deficits are highly prevalent. As a testimony to the success of the current strategy of care, the proportion of adults with Fontan circulation is increasing. Healthcare providers are ill-prepared to tackle these challenges, as well as specific needs such as contraception and pregnancy in female patients. The role of therapies such as cardiovascular drugs to prevent and treat complications, heart transplantation, and mechanical circulatory support remains undetermined. There is a clear need for consensus on how best to follow up patients with Fontan circulation and to treat their complications. This American Heart Association statement summarizes the current state of knowledge on the Fontan circulation and its consequences. A proposed surveillance testing toolkit provides recommendations for a range of acceptable approaches to follow-up care for the patient with Fontan circulation. Gaps in knowledge and areas for future focus of investigation are highlighted, with the objective of laying the groundwork for creating a normal quality and duration of life for these unique individuals.

Respiratory Training Late After Fontan Intervention: Impact on Cardiorespiratory Performance

Fontan palliation allows patients with "single ventricle" circulation to reach adulthood with an acceptable quality of life, although exercise tolerance is significantly reduced. To assess whether controlled respiratory training (CRT) increases cardiorespiratory performance. 16 Adolescent Fontan patients (age 17. 5 ± 3.8 years) were enrolled. Patients were divided into CRT group (n = 10) and control group (C group, n = 6). Maximal cardiopulmonary test (CPT) was repeated at the end of CRT in the CRT group and after an average time of 3 months in the C group. In the CRT group a CPT endurance was also performed before and after CRT. In the CRT group there was a significant improvement in cardiovascular and respiratory response to exercise after CRT. Actually, after accounting for baseline values, the CRT group had decreased breathing respiratory reserve (- 15, 95% CI -22.3 to - 8.0, p = 0.001) and increased RR peak (+ 4.8, 95% CI 0.7-8.9, p = 0.03), VE peak (+ 13.7, 95% CI 5.6-21.7, p = 0.004), VO₂ of predicted (+ 8.5, 95% CI 0.1-17.0, p = 0.05), VO₂ peak (+ 4.3, 95% CI 0.3 to 8.2, p = 0.04), and VO₂ workslope (+ 1.7, 95% CI 0.3-3.1, p = 0.02) as compared to the control group. Moreover, exercise endurance time increased from 8.45 to 17.7 min (p = 0.01). CRT improves cardiorespiratory performance in post-Fontan patients leading to a better aerobic capacity.

Diagnosis, Evaluation and Treatment of Pulmonary Arterial Hypertension in Children

Pulmonary Hypertension (PH), the syndrome of elevated pressure in the pulmonary arteries, is associated with significant morbidity and mortality for affected children. PH is associated with a wide variety of potential underlying causes, including cardiac, pulmonary, hematologic and rheumatologic abnormalities. Regardless of the cause, for many patients the natural history of PH involves progressive elevation in pulmonary arterial resistance and pressure, right ventricular dysfunction, and eventually heart failure. In recent years, a number of pulmonary arterial hypertension (PAH)-targeted therapies have become available to reduce pulmonary artery pressure and improve outcome. A growing body of evidence in both the adult and pediatric literature demonstrates enhanced quality of life, functional status, and survival among treated patients. This review provides a description of select etiologies of PH seen in pediatrics and an update on the most recent data pertaining to evaluation and management of children with PH/PAH. The available evidence for specific classes of PAH-targeted therapies in pediatrics is additionally discussed.

Rest and exercise hemodynamic and metabolic findings in active duty soldiers referred for cardiac catheterization to exclude heart disease: Insights from past invasive cardiopulmonary exercise testing using multisensor high fidelity catheters

OBJECTIVE

This study describes results of iCPET from the past, which used submaximal stress and multisensor high-fidelity catheters to exclude heart disease in a unique population of young adults.

BACKGROUND

There has been resurgence in comprehensive hemodynamic evaluation of complex cardiovascular patients. Although dynamic assessments during cardiac catheterization have become commonplace, there remains limited information regarding left and right heart hemodynamic changes during supine exercise in young adults.

METHODS

The study population was derived from a retrospective review of catheterization records at Brooke Army Medical Center for active duty patients (ages: 19-40 years) in whom hemodynamic waveforms were obtained with multisensor high-fidelity catheters and supine exercise testing (53.1 ± 12.6 watts) and angiography performed to exclude heart disease. We report findings from 41 males and 1 female (ages: 19-40 years) found free of heart disease.

RESULTS

Submaximal exercise was associated with ≈ fourfold (P < 0.001) increase in minute ventilation (VE), O₂ consumption (VO₂ ) and carbon dioxide production (VCO₂ ). VE/VCO₂ ratio decreased (-16.8 ± 13.9%, P < 0.001) and VE/VCO₂ slope was 22.6 ± 0.6 (±SE). Cardiac index (CI) increased with VO₂ (ΔCI/ΔVO₂ slope = 7.6 ± 2.2). Heart rate increased nearly 10 bpm per 100 mL O₂ /min/M² , whereas, changes in stroke volume were more variable. Pulmonary artery (PA) saturations fell from 77 to 55% (P < 0.001). No change was noted in mean right atrial pressures; PA pressures increased ≈10 mm Hg (P < 0.001). Pulmonary capillary wedge and left ventricular end-diastolic pressures increased ≈2 mm Hg (P < 0.001) but variability noted between individuals.

CONCLUSION

This study provides insight into past practices of invasive cardiopulmonary testing and furthers the understanding of metabolic and hemodynamic changes in a young population during supine submaximal exercise. © 2017 Wiley Periodicals, Inc.

Higher exercise intensity delays postexercise recovery of impedance-derived cardiac sympathetic activity

Systolic time intervals (STIs) provide noninvasive insights into cardiac sympathetic neural activity (cSNA). As the effect of exercise intensity on postexercise STI recovery is unclear, this study investigated the STI recovery profile after different exercise intensities. Eleven healthy males cycled for 8 min at 3 separate intensities: LOW (40%-45%), MOD (75%-80%), and HIGH (90%-95%) of heart-rate (HR) reserve. Bio-impedance cardiography was used to assess STIs - primarily pre-ejection period (PEP; inversely correlated with cSNA), as well as left ventricular ejection time (LVET) and PEP:LVET - during 10 min seated recovery immediately postexercise. Heart-rate variability (HRV), i.e., natural-logarithm of root mean square of successive differences (Ln-RMSSD), was calculated as an index of cardiac parasympathetic neural activity (cPNA). Higher preceding exercise intensity elicited a slower recovery of HR and Ln-RMSSD (p < 0.001), and these measures did not return to baseline by 10 min following any intensity (p ≤ 0.009). Recovery of STIs was also slower following higher intensity exercise (p ≤ 0.002). By 30 s postexercise, higher preceding intensity resulted in a lower PEP (98 ± 14 ms, 75 ± 6 ms, 66 ± 5 ms for LOW, MOD, and HIGH, respectively, p < 0.001). PEP recovered to baseline (143 ± 11 ms) by 5 min following LOW (139 ± 13 ms, p = 0.590) and by 10 min following MOD (145 ± 17 ms, p = 0.602), but was still suppressed at 10 min following HIGH (123 ± 21 ms, p = 0.012). Higher preceding exercise intensity attenuated the recovery of indices for cSNA (from STIs) and cPNA (from HRV) in a graded dose-response fashion. While exercise intensity must be considered, acute recovery may be a valuable period during which to concurrently monitor these noninvasive indices, to identify potentially abnormal cardiac autonomic responses.

Cardiac Autonomic Responses during Exercise and Post-exercise Recovery Using Heart Rate Variability and Systolic Time Intervals-A Review

Cardiac parasympathetic activity may be non-invasively investigated using heart rate variability (HRV), although HRV is not widely accepted to reflect sympathetic activity. Instead, cardiac sympathetic activity may be investigated using systolic time intervals (STI), such as the pre-ejection period. Although these autonomic indices are typically measured during rest, the “reactivity hypothesis” suggests that investigating responses to a stressor (e.g., exercise) may be a valuable monitoring approach in clinical and high-performance settings. However, when interpreting these indices it is important to consider how the exercise dose itself (i.e., intensity, duration, and modality) may influence the response. Therefore, the purpose of this investigation was to review the literature regarding how the exercise dosage influences these autonomic indices during exercise and acute post-exercise recovery. There are substantial methodological variations throughout the literature regarding HRV responses to exercise, in terms of exercise protocols and HRV analysis techniques. Exercise intensity is the primary factor influencing HRV, with a greater intensity eliciting a lower HRV during exercise up to moderate-high intensity, with minimal change observed as intensity is increased further. Post-exercise, a greater preceding intensity is associated with a slower HRV recovery, although the dose-response remains unclear. A longer exercise duration has been reported to elicit a lower HRV only during low-moderate intensity and when accompanied by cardiovascular drift, while a small number of studies have reported conflicting results regarding whether a longer duration delays HRV recovery. “Modality” has been defined multiple ways, with limited evidence suggesting exercise of a greater muscle mass and/or energy expenditure may delay HRV recovery. STI responses during exercise and recovery have seldom been reported, although limited data suggests that intensity is a key determining factor. Concurrent monitoring of HRV and STI may be a valuable non-invasive approach to investigate autonomic stress reactivity; however, this integrative approach has not yet been applied with regards to exercise stressors.

Model-Based Comparison of the Normal and Fontan Circulatory Systems-Part III

BACKGROUND

For patients with the Fontan circulatory arrangement, angiotensin-converting enzyme inhibition, guanylate cyclase activation, phosphodiesterase 5 inhibition, and endothelin receptor antagonism have so far resulted in little or no improvement in [Formula: see text] or peak cardiac index (CI), suggesting that our understanding of the factors that most impact the exercise hemodynamics is incomplete.

METHODS

To facilitate comparisons with clinical reports of the exercise performance of preadolescent Fontan patients, we rescaled our previously reported computational models of a two-year-old normal child and similarly aged Fontan patient, extended our Fontan model to capture the nonlinear relationship between flow and resistance quantified from previous computational fluid dynamic analyses of the total cavopulmonary connection (TCPC), and added respiration as well as skeletal muscle contraction.

RESULTS

(1) Without respiration, the computational model for both the normal and the Fontan cannot attain the values for CI at peak exercise reported in the clinical literature, (2) because flow through the TCPC is much greater during inspiration than during expiration, the effect on the CI of the dynamic (flow-related) TCPC resistance is much more dramatic during exercise than it is in breath-hold mode at rest, and (3) coupling breathing with skeletal muscle contraction leads to the highest augmentation of cardiac output, that is, the skeletal muscle pump is most effective when the intrathoracic pressure is at a minimum-at peak inspiration.

CONCLUSIONS

Novel insights emerge when a Fontan model incorporating dynamic TCPC resistance, full respiration, and skeletal muscle contraction can be compared to the model of the normal.

Differentiation of Impaired From Preserved Hemodynamics in Patients With Fontan Circulation Using Real-time Phase-velocity Cardiovascular Magnetic Resonance

Supplemental Digital Content is available in the text.

Purpose:

Progressive impairment of hemodynamics in patients with Fontan circulation is common, multifactorial, and associated with decreased quality of life and increased morbidity. We sought to assess hemodynamic differences between patients with preserved (preserved Fontans) and those with impaired circulation (impaired Fontans) after pulmonary vasodilation using oxygen and under forced breathing conditions.

Materials and Methods:

Real-time phase-contrast cardiovascular magnetic resonance was performed using non–ECG triggered echo-planar imaging (temporal resolution=24 to 28 ms) in the ascending aorta (AAo) and superior vena cava (SVC)/inferior vena cava (IVC) on room air, after 100% oxygen inhalation (4 L/min; 10 min) and on forced breathing in 29 Fontan patients (17.2±7.3 y) and in 32 controls on room air (13.4±3.7 y). The simultaneously recorded patients’ respiratory cycle was divided into 4 segments (expiration, end-expiration, inspiration, and end-inspiration) to generate respiratory-dependent stroke volumes (SVs). The imaging data were matched with physiological data and analyzed with home-made software.

Results:

The mean SV_i (AAo) was 46.1±11.1 mL/m² in preserved Fontans versus 30.4±6.2 mL/m² in impaired Fontans (P=0.002) and 51.1±6.9 mL/m² in controls (P=0.107). The cutoff value for differentiation of Fontan groups was SV_i (AAo, end-expiratory) of 32.1 mL/m². After hyperoxygenation, the mean SV_i (AAo) increased to 48.7±12.7 mL/m² in preserved Fontans (P=0.045) but remained unchanged in impaired Fontans (31.1±5.8 mL/m², P=0.665). Simultaneously, heart rates decreased from 75.2±15.9 to 70.8±16.4 bpm (preserved; P=0.000) but remained unchanged in impaired circulation (baseline: 84.1±9.8 bpm, P=0.612). Compared with physiological respiration, forced breathing increased the maximum respiratory-related cardiac index difference (ΔCI_max) in preserved Fontans (SVC: 2.5-fold, P=0.000; and IVC: 1.8-fold, P=0.000) and to a lower extent in impaired Fontans (both veins, 1.5-fold; P(SVC)=0.011, P(IVC)=0.013). There was no impact on mean blood flow.

Conclusions:

Oxygen affected the pulmonary vascular system by vasodilation and increased SV_i in preserved Fontans but had no effect on impaired Fontans. Forced breathing increased ΔCI_max but did not change the mean blood flow by sole activation of the ventilatory pump. End-expiratory aortic SV_i represents a valuable measure for classifying the severity of Fontan hemodynamics impairment.

Outcome after cardiopulmonary resuscitation in patients with congenital heart disease

Background:

Outcome after cardiopulmonary resuscitation (CPR) in patients with underlying congenital heart disease is uncertain. This study aimed at evaluating outcome after CPR in patients with underlying congenital heart disease, factors related to worse outcome after CPR and whether survivors of sudden cardiac death (SCD) have a worse outcome when compared to an age, gender and disease-matched control population.

Methods:

Between 1984 and 2015, all patients with congenital heart disease who received in or out-of-hospital CPR were identified from the database of congenital heart disease from the University Hospitals Leuven. Postoperative and neonatal (<6 months of age) CPR was excluded. For each survivor of SCD, two control patients matched for gender, age and underlying heart defect were included in the study.

Results:

Thirty-eight patients (66% men; median age 25 years (interquartile range 9–40); 68% out-of-hospital) were identified, of which 27 (66%) survived the event. The main cause of SCD was ventricular tachycardia or fibrillation ( n=21). Heart defect complexity (odds ratio (OR) 5.1; 95% confidence interval (CI) 1.2–21.9; P=0.027), pulmonary hypertension (OR 13.8; 95% CI 2.1–89.5; P=0.006) and time to return of spontaneous circulation (OR 1.1; 95% CI 1.0–1.1; P=0.046) were related to worse outcome. Survivors of SCD had a worse prognosis when compared to an age, gender and disease-matched control group (5-year survival 76% vs. 98%; P=0.002).

Conclusions:

The complexity of underlying heart defect, pulmonary hypertension and time to return of spontaneous circulation are related to worse outcome in the case of CPR. Survivors of SCD have a worse outcome when compared to matched controls, indicating the need for adequate implantable cardioverter defibrillator indication assessment and for stringent follow-up of patients with worsening haemodynamics.

Endothelin inhibitors lower pulmonary vascular resistance and improve functional capacity in patients with Fontan circulation

OBJECTIVES

To evaluate the effects of endothelin inhibitors (ERAs) on hemodynamic and functional parameters in patients post-Fontan procedure with high pulmonary vascular resistance (PVR).

METHODS

Among our cohort of patients with Fontan circulation, 8 children, 8 adolescents, and 8 adults had PVR ≥2 WU*m². These patients were treated with ERAs (minors with bosentan, adults with macitentan) and reevaluated after 6 months. Pre- and posttreatment hemodynamic variables were assessed by cardiac catheterization. Functional capacity was evaluated by cardiopulmonary exercise testing (CPET). Our primary endpoint was to obtain a reduction of PVR; the secondary endpoint was to obtain an improvement of functional capacity.

RESULTS

Under treatment, New York Heart Association class improved for adolescents and adults. PVR decreased (P = .01) in all groups: in children from the median value 2.3 (interquartile range 2.0-3.1) to 1.9 (1.4-2.3) WU*m², in adolescents from 2.3 (2.1-2.4) to 1.7 (1.4-1.8) WU*m², and in adults from 2.8 (2.0-4.7) to 2.1 (1.8-2.8)WU*m². In 71% of patients, PVR fell to less than 2 WU*m². Cardiac index increased in adolescents from 2.6 (2.4-3.3) to 3.6 (3.4-4.3) L/min/m², P = .04, and in adults from 2.1 (2.0-2.3) to 2.8 (2.3-4.7) L/min/m², P = .03. CPET showed that only adolescents displayed a significant functional improvement. Anaerobic threshold improved from 17 (13-19) to 18 (13-20) mL/kg/min, P = .03; oxygen consumption and VO₂ max increased from 1.3 (1.0-1.6) to 1.7 (1.1-1.9) L/min, P = .02 and from 25 (21-28) to 28 (26-31) L/min, P = .02, respectively. Oxygen pulse increased from 7.9 (5.7-10.4) to 11.2 (8.2-13.0) L/beat, P = .01.

CONCLUSIONS

This is the first study that assesses by cardiac catheterization and CPET the effects of ERA in patients with Fontan circulation with increased PVR. These results suggest that ERAs might provide most pronounced hemodynamic and functional improvement in adults and adolescents.

Managing adult Fontan patients: where do we stand?

The Fontan operation is performed as a palliative procedure to improve survival in infants born with a functionally univentricular circulation. The success of the operation is demonstrated by a growing adult Fontan population that exists with this unique physiology. Late follow-up has demonstrated expected and unexpected sequelae, and has shown multisystem effects of this circulation. This review discusses the challenges of managing the late complications in terms of understanding this unique physiology and the innovative therapeutic interventions that are being investigated. The challenge remains to maintain quality of life for adult survivors, as well as extending life expectancy.

Innovative solutions are required to meet the challenges of the Fontan circulation faced in adult lifehttp://ow.ly/XTSm305oH8b

Cardiopulmonary Interactions

OBJECTIVES

The objectives of this review are to discuss the mechanisms by which respiration impacts cardiovascular function and vice versa, with an emphasis on the impact of these interactions in pediatric cardiac critical care.

DATA SOURCE

A search of MEDLINE was conducted using PubMed.

CONCLUSIONS

In the presence of underlying cardiac and respiratory disease, the interplay between these two systems is significant and plays a pivotal role in the pathophysiology of acute and chronic phases of a wide spectrum of diseases. An understanding of these relationships is essential to optimizing the care of critically ill patients.

Pulmonary Hypertension in Children

The prevalence of PH is increasing in the pediatric population, because of improved recognition and increased survival of patients, and remains a significant cause of morbidity and mortality. Recent studies have improved the understanding of pediatric PH, but management remains challenging because of a lack of evidence-based clinical trials. The growing contribution of developmental lung disease requires dedicated research to explore the use of existing therapies as well as the creation of novel therapies. Adequate study of pediatric PH will require multicenter collaboration due to the small numbers of patients, multifactorial disease causes, and practice variability.

The Fontan circulation after 45 years: update in physiology

The Fontan operation was first performed in 1968. Since then, this operation has been performed on thousands of patients worldwide. Results vary from very good for many decades to very bad with a pleiad of complications and early death. A good understanding of the physiology is necessary to further improve results. The Fontan connection creates a critical bottleneck with obligatory upstream congestion and downstream decreased flow; these two features are the basic cause of the majority of the physiologic impairments of this circulation. The ventricle, while still the engine of the circuit, cannot compensate for the major flow restriction of the Fontan bottleneck: the suction required to compensate for the barrier effect cannot be generated, specifically not in a deprived heart. Except for some extreme situations, the heart therefore no longer controls cardiac output nor can it significantly alter the degree of systemic venous congestion. Adequate growth and development of the pulmonary arteries is extremely important as pulmonary vascular impedance will become the major determinant of Fontan outcome. Key features of the Fontan ventricle are early volume overload and overgrowth, but currently chronic preload deprivation with increasing filling pressures. A functional decline of the Fontan circuit is expected and observed as pulmonary vascular resistance and ventricular filling pressure increase with time. Treatment strategies will only be successful if they open up or bypass the critical bottleneck or act on immediate surroundings (impedance of the Fontan neoportal system, fenestration, enhanced ventricular suction).

Decision-Making for Surgery in the Management of Patients with Univentricular Heart

A series of technical refinements over the past 30 years, in combination with advances in perioperative management, have resulted in dramatic improvements in the survival of patients with univentricular heart. While the goal of single-ventricle palliation remains unchanged - normalization of the pressure and volume loads on the systemic ventricle, the strategies to achieve that goal have become more diverse. Optimal palliation relies on a thorough understanding of the changing physiology over the first years of life and the risks and consequences of each palliative strategy. This review describes how to optimize surgical decision-making in univentricular patients based on a current understanding of anatomy, physiology, and surgical palliation.

Central cardiac limit to aerobic capacity in patients with exertional pulmonary venous hypertension: implications for heart failure with preserved ejection fraction

BACKGROUND

The mechanism of functional limitation in heart failure with preserved ejection fraction remains controversial. We examined the contributions of central cardiac and peripheral mechanisms and hypothesized that the pulmonary vascular response to exercise is an important determinant of aerobic capacity among patients with exertional pulmonary venous hypertension (ePVH).

METHODS AND RESULTS

We compared 31 ePVH patients (peak VO2<80% of predicted and peak pulmonary arterial wedge pressure≥20 mm Hg) with 31 age- and sex-matched controls (peak VO2>80% predicted) who underwent invasive cardiopulmonary exercise testing for unexplained exertional intolerance. ePVH patients had lower peak cardiac output (73±14% versus 103±18% predicted; P<0.001) compared with controls, related both to impaired chronotropic response (peak heart rate 111±25 beats per minute versus 136±24 beats per minute; P<0.001) and to reduced peak stroke volume index (47±10 mL/min per m(2) versus 54±15 mL/min per m(2); P=0.03). Peak systemic O2 extraction was not different between groups (arterial-mixed venous oxygen content difference: 13.0±2.1 mL/dL versus 13.4±2.4 mL/dL; P=0.46). ePVH patients had higher resting (150±74 versus 106±50 dyne/s per cm(-5); P=0.009), peak (124±74 dyne/s per cm(-5) versus 70±41 dyne/s per cm(-5); P<0.001), and isoflow pulmonary vascular resistance (124±74 dyne/s per cm(-5) versus 91±33 dyne/s per cm(-5) at cardiac output≈10.6 L/min; P=0.04). Pulmonary vascular resistance decreased with exercise in all control subjects but increased in 36% (n=11) of ePVH patients. Abnormal pulmonary vascular response was not associated with peak VO2.

CONCLUSIONS

Reduced cardiac output response, rather than impaired peripheral O2 extraction, constrains oxygen delivery and aerobic capacity in ePVH. Pulmonary vascular dysfunction is common in patients with ePVH at rest and during exercise.

Bosentan Improves Exercise Capacity in Adolescents and Adults After Fontan Operation

Background—

The Fontan procedure has improved survival in children with functionally univentricular hearts. With time, however, complications such as reduced exercise capacity are seen more frequently. Exercise intolerance is multifactorial, but pulmonary vascular resistance probably plays a crucial role. Elevated pulmonary vascular resistance has been associated with raised levels of endothelin-1, which are common both before and after Fontan operations. Treatment with endothelin-1 receptor antagonists could theoretically improve cardiopulmonary hemodynamics and exercise capacity. The aim of this study was therefore to examine the efficacy and safety of bosentan in Fontan patients.

Methods and Results—

Seventy-five adolescents and adults were randomized 1:1 to 14 weeks of treatment with bosentan or placebo. Cardiopulmonary exercise test, functional class, blood samples, and quality-of-life questionnaires were evaluated at baseline and at the end of treatment. Sixty-nine patients (92%) completed the study. Peak oxygen consumption increased 2.0 mL·kg −1 ·min −1 (from 28.7 to 30.7 mL·kg −1 ·min −1 ) in the bosentan group compared with 0.6 mL·kg −1 ·min −1 (from 28.4 to 29.0 mL·kg −1 ·min −1 ) in the placebo group ( P =0.02). Cardiopulmonary exercise test time increased by 0.48 minute (from 6.79 to 7.27 minutes) versus 0.08 minute (from 6.94 to 7.02 minutes; P =0.04). Nine bosentan-treated patients improved 1 functional class, whereas none improved in the placebo group ( P =0.0085). Side effects were mild and occurred equally in both groups. No serious adverse effects were seen, and no patients had liver enzyme levels above the 3-fold upper limit.

Conclusions—

Bosentan improves exercise capacity, exercise time, and functional class in Fontan patients without serious adverse events or hepatotoxicity.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01292551.