Reduced ascending aorta distensibility relates to adverse ventricular mechanics in patients with hypoplastic left heart syndrome: noninvasive study using wave intensity analysis

Predicting the effects of surgically determined parameters on exercise tolerance in Fontan patients

The Fontan physiology is a surgically created circulation for patients with a single functioning ventricle. Patients with this circulation tend to have lower exercise tolerance compared to those with a normal circulation. Important computational and experimental work has been done to investigate this reduction in exercise tolerance. However, there are few systematic modeling studies that focus on the effect of several surgically determined parameters within the same framework. We propose a mathematical model to describe the Fontan circulation under exercise. We then formulate a heuristic based on clinical data from Fontan patients to estimate exercise tolerance. The model is used to investigate the effect of three important surgically determined parameters on exercise tolerance: the systemic arterial compliance, the systemic-venous to pulmonary-venous fenestration, and the resistance of the total cavopulmonary connection.

Bilateral pulmonary artery banding facilitates the systemic ventricular outflow tract growth for biventricular and univentricular repair candidates of complex arch anomaly

Various surgical approaches address complex heart disease with arch anomalies. Bilateral pulmonary artery banding (bPAB) is a strategy for critically ill patients with complex arch anomalies. Some reports argued the potential effect of bPAB on the growth of the left ventricular outflow tract (LVOT) during inter-stage after bPAB. This study aimed to analyze the LVOT growth for biventricular repair candidates with arch anomaly and systemic ventricular outflow tract (SVOT) for univentricular repair candidates with arch anomaly. This retrospective study analyzed 17 patients undergoing initial bPAB followed by arch repair. The Z-scores of LVOT and SVOT were compared between pre-bPAB and pre-arch repair. Patient characteristics, transthoracic echocardiogram data, and PAB circumferences were reviewed. The diameter of the minimum LVOT for biventricular repair (BVR) candidates, the pulmonary valve (neo-aortic valve, neo-AoV) and the pulmonary trunk (the neo-ascending aorta, neo-AAo) for univentricular repair (UVR) candidates, and the degree of aortic or neo-aortic insufficiency in each candidate was statistically analyzed. 17 patients were divided into the UVR candidates (group U) with 9 patients and the BVR candidates (group B) with 8 patients. In group B, the median value of the Z-score of the minimum LVOT increased from -3.2 (range: - 4.1 ~ - 1.0) at pre-PAB to -2.8 (range: - 3.6 ~ - 0.3) at pre-arch repair with a significant difference (p = 0.012). In group U, the median value of the Z-score of the neo-AoV increased from 0.5 (range: - 1.0 ~ 1.7) at pre-bPAB to 1.2 (range: 0.2 ~ 1.9) at pre-arch repair with a significant difference (p < 0.01). The median value of the Z-score of the neo-AAo was also increased from 3.1 (range: 1.5 ~ 4.6) to 4.3 (range: 3.1 ~ 5.9) with a significant difference (p = 0.028). The growth of the LVOT for BVR candidates and SVOT for UVR candidates during the inter-stage between bPAB and arch repair was observed. These results suggest the potential advantage of bPAB in surgical strategies. Further research is needed to validate these findings and refine surgical approaches.

Non-invasive Assessment by B-Mode Ultrasound of Arterial Pulse Wave Intensity and Its Reduction During Ventricular Dysfunction

Arterial pulse waves contain clinically useful information about cardiac performance, arterial stiffness and vessel tone. Here we describe a novel method for non-invasively assessing wave properties, based on measuring changes in blood flow velocity and arterial wall diameter during the cardiac cycle. Velocity and diameter were determined by tracking speckles in successive B-mode images acquired with an ultrafast scanner and plane-wave transmission. Blood speckle was separated from tissue by singular value decomposition and processed to correct biases in ultrasound imaging velocimetry. Results obtained in the rabbit aorta were compared with a conventional analysis based on blood velocity and pressure, employing measurements obtained with a clinical intra-arterial catheter system. This system had a poorer frequency response and greater lags but the pattern of net forward-traveling and backward-traveling waves was consistent between the two methods. Errors in wave speed were also similar in magnitude, and comparable reductions in wave intensity and delays in wave arrival were detected during ventricular dysfunction. The non-invasive method was applied to the carotid artery of a healthy human participant and gave a wave speed and patterns of wave intensity consistent with earlier measurements. The new system may have clinical utility in screening for heart failure.

A computational study of aortic reconstruction in single ventricle patients

Patients with hypoplastic left heart syndrome (HLHS) are born with an underdeveloped left heart. They typically receive a sequence of surgeries that result in a single ventricle physiology called the Fontan circulation. While these patients usually survive into early adulthood, they are at risk for medical complications, partially due to their lower than normal cardiac output, which leads to insufficient cerebral and gut perfusion. While clinical imaging data can provide detailed insight into cardiovascular function within the imaged region, it is difficult to use these data for assessing deficiencies in the rest of the body and for deriving blood pressure dynamics. Data from patients used in this paper include three-dimensional, magnetic resonance angiograms (MRA), time-resolved phase contrast cardiac magnetic resonance images (4D-MRI) and sphygmomanometer blood pressure measurements. The 4D-MRI images provide detailed insight into velocity and flow in vessels within the imaged region, but they cannot predict flow in the rest of the body, nor do they provide values of blood pressure. To remedy these limitations, this study combines the MRA, 4D-MRI, and pressure data with 1D fluid dynamics models to predict hemodynamics in the major systemic arteries, including the cerebral and gut vasculature. A specific focus is placed on studying the impact of aortic reconstruction occurring during the first surgery that results in abnormal vessel morphology. To study these effects, we compare simulations for an HLHS patient with simulations for a matched control patient that has double outlet right ventricle (DORV) physiology with a native aorta. Our results show that the HLHS patient has hypertensive pressures in the brain as well as reduced flow to the gut. Wave intensity analysis suggests that the HLHS patient has irregular circulatory function during light upright exercise conditions and that predicted wall shear stresses are lower than normal, suggesting the HLHS patient may have hypertension.

Unlocking the Non-invasive Assessment of Conduit and Reservoir Function in the Aorta

Aortic surgeries in congenital conditions, such as hypoplastic left heart syndrome (HLHS), aim to restore and maintain the conduit and reservoir functions of the aorta. We proposed a method to assess these two functions based on 4D flow MRI, and we applied it to study the aorta in pre-Fontan HLHS. Ten pre-Fontan HLHS patients and six age-matched controls were studied to derive the advective pressure difference and viscous dissipation for conduit function, and pulse wave velocity and elastic modulus for reservoir function. The reconstructed neo-aorta in HLHS subjects achieved a good conduit function at a cost of an impaired reservoir function (69.7% increase of elastic modulus). The native descending HLHS aorta displayed enhanced reservoir (elastic modulus being 18.4% smaller) but impaired conduit function (three-fold increase in peak advection). A non-invasive and comprehensive assessment of aortic conduit and reservoir functions is feasible and has potentially clinical relevance in congenital vascular conditions.

Arterial Stiffness in Congenital Heart Disease

Transposition of the great arteries (TGA), coarctation of the aorta (CoA), single ventricle (SV) and tetralogy of Fallot (ToF) are forms of congenital heart disease (CHD). Despite advances in treatment, cardiovascular and cerebrovascular complications in patients with repaired CHD occur earlier in life compared to healthy subjects. A factor that may contribute to this increased risk is elevated arterial stiffness. This systematic review provides a critical assessment of current evidence on central arterial stiffness in patients with CHD compared to healthy controls. In July 2020, Medline OVID, EMBASE and Scopus were searched using keywords and MeSH terms. Articles were included if they reported indices of aortic or carotid artery stiffness in patients with TGA, CoA, SV or ToF, and compared these to controls. Additional studies were screened from the reference lists of included articles. Of 1,033 studies identified, 43 were included in the final review. Most studies identified at least one index of central arterial stiffness, commonly in the aortic root or ascending aorta, that was higher in patients with CHD compared to controls. The commonly reported surrogate markers of stiffness were pulse wave velocity, aortic distensibility and the β stiffness index. There was a relatively small number of original studies, and synthesis of data was limited by methodological heterogeneity, highlighting the need for further studies with standardised methods. However, there was consistent evidence of early and/or accelerated arterial stiffening in CHD patients, which may contribute to the increased risk of adverse cardiovascular and cerebrovascular events in this population.

Assessing Single Ventricle Function in the Fontan Circulation using Wave Intensity Analysis

Single ventricle hearts palliated with the Fontan operation present complications later in life as a result of increased venous pressures and abnormal ventricle function. Wave intensity analysis uses measurements of blood velocity and pressure to represent arterial hemodynamics as summations of energy waves. This methodology could potentially be a useful tool in assessment of Fontan patients. The clinical value of wave intensity parameters was utilized to evaluate the functional performance of the single ventricle in Fontan patients. A retrospective analysis of invasive hemodynamic data was retrospectively obtained from routine cardiac catheterization of patients with Fontan circulation (n = 20) and comparison to those with biventricular circulation (n = 10) who presented to the catheterization laboratory for closure of small patent ductus arteriosus (PDAs). Wave intensity analysis and wave energy flux was calculated using aortic pressure waveforms and echocardiography aortic Doppler measurements as previously described. Significant differences were seen in the peak forward compression wave (p = 0.013), early systolic energy flux (p = 0.005) and the systolic and diastolic ratio (p = 0.006) in Fontan patients versus controls. Within the Fontan group, there was a positive correlation (0.54, p = 0.02) between the wave speed and pulmonary vascular resistance. Early systolic energy flux was a potential individual indicator of a Fontan patients heart failure classification (AUC = 0.71). Wave intensity analysis could be a useful tool in screening Fontan patients and predicting clinical outcomes and Fontan failure. Future prospective analyses of Fontan hemodynamics and WIA are needed.

High-degree Norwood neoaortic tapering is associated with abnormal flow conduction and elevated flow-mediated energy loss

OBJECTIVE

The Norwood neoaortic arch biomechanical properties are abnormal due to reduced vessel wall compliance and abnormal geometry. Others have previously described neoaortic geometric distortion by the degree of diameter reduction (tapering) and associated this with mismatched ventricular-neoaortic coupling, abnormal flow hemodynamic parameters, and worse patient outcome. Our purposes were to investigate the influence of neoaortic tapering (ie, diameter reduction) on flow-mediated viscous energy loss (E_L') in post-Norwood palliated hypoplastic left heart syndrome patients, and correlate flow-geometry with single ventricle power generation.

METHODS

Twenty-six palliated hypoplastic left heart syndrome patients underwent comprehensive cardiac evaluation with 4-dimensional-flow magnetic resonance imaging. Patients were grouped into high- (group H, n = 13) and low- (group L, n = 13) degree neoaortic tapering using the median cutoff value of neoaortic diameter variance. E_L' was calculated along standardized segments using 4-dimensional-flow magnetic resonance imaging. Flow-mediated power loss as a percentage of total power generated by the single ventricle was determined.

RESULTS

Group H had a higher prevalence of abnormal recirculating flow in the neoaorta and elevated neoaortic E_L' in the ascending aorta (1.0 vs 0.6 mW; P = .004). Group H E_L' was increased across the entire thoracic aorta (2.6 vs 1.3 mW; P = .002) and accounted for 0.7% of generated ventricular power versus 0.3% in group L (P = .024). E_L' directly correlated with the degree of ascending aortic dilation (R = 0.49; P = .012).

CONCLUSIONS

Patients with high degree neoaortic tapering have more perturbed flow through the neoaorta and increased E_L'. Flow-mediated energy loss due to abnormal flow represents irreversibly wasted power generated by the single right ventricle. In patients with high-degree neoaortic tapering, E_L' was more than 2-fold greater than low-degree tapering patients. These data suggest that oversizing the Norwood neoaortic reconstruction should be avoided and that patients with distorted neoaortic geometry may warrant increased surveillance for single-ventricle deterioration.

Patients with Fontan circulation have abnormal aortic wave propagation patterns: A wave intensity analysis study

BACKGROUND

Elevated systemic afterload in patients with Fontan circulation may lead to impaired single ventricular function. Wave intensity analysis (WIA) enables evaluation of compression and expansion waves traveling through vasculature. We aimed to investigate the unfavorable wave propagation causing excessive afterload may be an important contributor to the overall single ventricle function and to the limited functional capacity in this patient population.

METHODS

Patients with hypoplastic left heart syndrome (HLHS) (n = 25), single left ventricle (SLV) (n = 24), and normal controls (n = 10) underwent phase-contrast MRI based WIA analysis evaluated in the ascending aorta. Forward compression wave (FCW) representing dP/dt, backward compression wave (BCW) reflecting vascular stiffness, and forward decompression wave (FDW) representing LV relaxation were recorded and indexed to each other.

RESULTS

FCW was lowest in HLHS patients (1098 mm⁵/s), and higher in the SLV group (1457 mm5/s), and controls (6457 mm5/s) (P < 0.001). BCW/FCW was increased in HLHS (0.22) and SLV (0.14) groups compared to controls (0.08) (P = 0.003). Peak VO2 correlated with FCW (R = 0.50, P = 0.015), stroke volume (R = 0.72, P < 0.001), and cardiac output (R = 0.44, P = 0.034).

CONCLUSIONS

Patients with HLHS and SLV have unfavorable aortic WIA patterns with increased BCW/FCW ratio indicating increased systemic afterload due to retrograde compression waves. Reduced FCW and systolic MRI indices correlated with peak VO2 suggesting that abnormal systolic wave propagation may play a role in exercise intolerance for Fontan patients.

Feasibility of Wave Intensity Analysis in Patients With Conotruncal Anomalies Before and After Pregnancy: New Physiological Insights?

Background: Conotruncal anomalies (CTA) are associated with ongoing dilation of the aortic root, as well as increased aortic stiffness, which may relate to intrinsic properties of the aorta. Pregnancy hormones lead to hemodynamic changes and remodeling of the tunica media, resulting in the opposite effect, i.e., increasing distensibility. These changes normalize post-pregnancy in healthy women but have not been fully investigated in CTA patients. Methods: We examined aortic distensibility and ventriculo-arterial coupling before and after pregnancy using cardiovascular magnetic resonance (CMR)-derived wave intensity analysis (WIA). Pre- and post-pregnancy CMR data were retrospectively analyzed. Aortic diameters were measured before, during, and after pregnancy by cardiac ultrasound and before and after pregnancy by CMR. Phase contrast MR flow sequences were used for calculating wave speed (c) and intensity (WI). A matched analysis was performed comparing results before and after pregnancy. Results: Thirteen women (n = 5, transposition of the great arteries; n = 6, tetralogy of Fallot; n = 1, double outlet right ventricle, n = 1, truncus arteriosus) had 19 pregnancies. Median time between delivery and second CMR was 2.3 years (range: 1-6 years). The aortic diameter increased significantly after pregnancy in nine (n = 9) patients by a median of 4 ± 2.3 mm (range: 2-7.0 mm, p = 0.01). There was no difference in c pre-/post-pregnancy (p = 0.73), suggesting that increased compliance, typically observed during pregnancy, does not persist long term. A significant inverse relationship was observed between c and heart rate (HR) after pregnancy (p = 0.01, r = 0.73). There was no significant difference in cardiac output, aortic/pulmonary regurgitation, or WI peaks pre-/post-pregnancy. Conclusions: WIA is feasible in this population and could provide physiological insights in larger cohorts. Aortic distensibility and wave intensity did not change before and after pregnancy in CTA patients, despite an increase in diameter, suggesting that pregnancy did not adversely affect coupling in the long-term.

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.

Relationship of Aortic Stiffness to Exercise and Ventricular Volumes in Single Ventricles

BACKGROUND

Patients with single ventricle (SV) may often undergo aortic reconstruction that creates a stiff large vessel, increasing afterload and affecting exercise performance. The objective of this study was to determine the relationship of pulse wave velocity (PWV) and distensibility in reconstructed and normal aortic arches after Fontan with exercise variables.

METHODS

PWV and distensibility of the descending aorta at the level of the diaphragm (DAo) were calculated with real-time exercise cardiac magnetic resonance in 48 patients with SV after Fontan (18 after aortic reconstruction; 30 without aortic reconstruction) and compared with metabolic exercise stress test variables.

RESULTS

PWV was greater in the reconstructed group than in the non-reconstructed group (median 4.4 m/s [range: 2.3 to 9.8 m/s] versus 3.6 [range: 2.6 to 6.3 m/s], respectively, p = 0.003). Statistically significant inverse correlations were found between PWV and end-diastolic, end-systolic, and stroke volumes at rest and at exercise in the reconstructed group. In addition, inverse correlations also existed in the reconstructed group between distensibility of the DAo and the exercise variables such as peak oxygen pulse (R = 0.56, p = 0.02), peak oxygen consumption (R = 0.63, p = 0.008), oxygen consumption at ventilatory anaerobic threshold (R = 0.48, p = 0.04), and peak work (R = 0.54, p = 0.02). Similar correlations were not seen in patients with non-reconstructed aortas.

CONCLUSIONS

Patients with SV with reconstructed aortas have increased aortic stiffness, increasing afterload on the ventricle. Native DAo stiffness distal to the reconstruction is inversely correlated with exercise performance, presumably to decrease impedance mismatch to maintain homogeneity of the aortic wall. This information suggests a possible mechanism for decreased exercise performance in patients with SV with aortic reconstructions.

Noninvasive wave intensity analysis predicts functional worsening in children with pulmonary arterial hypertension

The purpose of the present study was to characterize pulmonary vascular stiffness using wave intensity analysis (WIA) in children with pulmonary arterial hypertension (PAH), compare the WIA indexes with catheterization- and MRI-derived hemodynamics, and assess the prognostic ability of WIA-derived biomarkers to predict the functional worsening. WIA was performed in children with PAH ( n = 40) and healthy control subjects ( n = 15) from phase-contrast MRI-derived flow and area waveforms in the main pulmonary artery (MPA). From comprehensive WIA spectra, we collected and compared with healthy control subjects forward compression waves (FCW), backward compression waves (BCW), forward decompression waves (FDW), and wave propagation speed ( c-MPA). There was no difference in the magnitude of FCW between PAH and control groups (88 vs. 108 mm⁵·s^-1·ml^-1, P = 0.239). The magnitude of BCW was increased in patients with PAH (32 vs. 5 mm⁵·s^-1·ml^-1, P < 0.001). There was no difference in magnitude of indexed FDW (32 vs. 28 mm⁵·s^-1·ml^-1, P = 0.856). c-MPA was increased in patients with PAH (3.2 vs. 1.6 m/s, P < 0.001). BCW and FCW correlated with mean pulmonary arterial pressure, right ventricular volumes, and ejection fraction. Elevated indexed BCW [heart rate (HR) = 2.91, confidence interval (CI): 1.18-7.55, P = 0.019], reduced indexed FDW (HR = 0.34, CI: 0.11-0.90, P = 0.030), and increased c-MPA (HR = 3.67, CI: 1.47-10.20, P = 0.004) were strongly associated with functional worsening of disease severity. Our results suggest that noninvasively derived biomarkers of pulmonary vascular resistance and stiffness may be helpful for determining prognosis and monitoring disease progression in children with PAH. NEW & NOTEWORTHY Wave intensity analysis (WIA) studies are lacking in children with pulmonary arterial hypertension (PAH) partially because WIA, which is necessary to assess vascular stiffness, requires an invasive pressure-derived waveform along with simultaneous flow measurements. We analyzed vascular stiffness using WIA in children with PAH who underwent phase-contrast MRI and observed significant differences in WIA indexes between patients with PAH and control subjects. Furthermore, WIA indexes were predictive of functional worsening and were associated with standard catheterization measures.

Virtual medicine: Utilization of the advanced cardiac imaging patient avatar for procedural planning and facilitation

Advances in imaging technology have led to a paradigm shift from planning of cardiovascular procedures and surgeries requiring the actual patient in a "brick and mortar" hospital to utilization of the digitalized patient in the virtual hospital. Cardiovascular computed tomographic angiography (CCTA) and cardiovascular magnetic resonance (CMR) digitalized 3-D patient representation of individual patient anatomy and physiology serves as an avatar allowing for virtual delineation of the most optimal approaches to cardiovascular procedures and surgeries prior to actual hospitalization. Pre-hospitalization reconstruction and analysis of anatomy and pathophysiology previously only accessible during the actual procedure could potentially limit the intrinsic risks related to time in the operating room, cardiac procedural laboratory and overall hospital environment. Although applications are specific to areas of cardiovascular specialty focus, there are unifying themes related to the utilization of technologies. The virtual patient avatar computer can also be used for procedural planning, computational modeling of anatomy, simulation of predicted therapeutic result, printing of 3-D models, and augmentation of real time procedural performance. Examples of the above techniques are at various stages of development for application to the spectrum of cardiovascular disease processes, including percutaneous, surgical and hybrid minimally invasive interventions. A multidisciplinary approach within medicine and engineering is necessary for creation of robust algorithms for maximal utilization of the virtual patient avatar in the digital medical center. Utilization of the virtual advanced cardiac imaging patient avatar will play an important role in the virtual health care system. Although there has been a rapid proliferation of early data, advanced imaging applications require further assessment and validation of accuracy, reproducibility, standardization, safety, efficacy, quality, cost effectiveness, and overall value to medical care.

Increased arterial stiffness in children with congenital heart disease

Objective Central systolic blood pressure (SBP) is a measure of arterial stiffness and strongly associated with atherosclerosis and end-organ damage. It is a stronger predictor of cardiovascular events and all-cause mortality than peripheral SBP. In particular, for children with congenital heart disease, a higher central SBP might impose a greater threat of cardiac damage. The aim of the study was to analyse and compare central SBP in children with congenital heart disease and in healthy counterparts. Patients and methods Central SBP was measured using an oscillometric method in 417 children (38.9% girls, 13.0 ± 3.2 years) with various congenital heart diseases between July 2014 and February 2017. The test results were compared with a recent healthy reference cohort of 1466 children (49.5% girls, 12.9 ± 2.5 years). Results After correction for several covariates in a general linear model, central SBP of children with congenital heart disease was significantly increased (congenital heart disease: 102.1 ± 10.2 vs. healthy reference cohort: 100.4 ± 8.6, p < .001). The analysis of congenital heart disease subgroups revealed higher central SBP in children with left heart obstructions (mean difference: 3.6 mmHg, p < .001), transpositions of the great arteries after arterial switch (mean difference: 2.2 mmHg, p = .017) and univentricular hearts after total cavopulmonary connection (mean difference: 2.1 mmHg, p = .015) compared with the reference. Conclusion Children with congenital heart disease have significantly higher central SBP compared with healthy peers, predisposing them to premature heart failure. Screening and long-term observations of central SBP in children with congenital heart disease seems warranted in order to evaluate the need for treatment.

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.

Experimental Study of Anisotropic Stress/Strain Relationships of Aortic and Pulmonary Artery Homografts and Synthetic Vascular Grafts

Homografts and synthetic grafts are used in surgery for congenital heart disease (CHD). Determining these materials' mechanical properties will aid in understanding tissue behavior when subjected to abnormal CHD hemodynamics. Homograft tissue samples from anterior/posterior aspects, of ascending/descending aorta (AA, DA), innominate artery (IA), left subclavian artery (LScA), left common carotid artery (LCCA), main/left/right pulmonary artery (MPA, LPA, RPA), and synthetic vascular grafts, were obtained in three orientations: circumferential, diagonal (45 deg relative to circumferential direction), and longitudinal. Samples were subjected to uniaxial tensile testing (UTT). True strain-Cauchy stress curves were individually fitted for each orientation to calibrate Fung model. Then, they were used to calibrate anisotropic Holzapfel–Gasser model (R2 > 0.95). Most samples demonstrated a nonlinear hyperelastic strain–stress response to UTT. Stiffness (measured by tangent modulus at different strains) in all orientations were compared and shown as contour plots. For each vessel segment at all strain levels, stiffness was not significantly different among aspects and orientations. For synthetic grafts, stiffness was significantly different among orientations (p < 0.042). Aorta is significantly stiffer than pulmonary artery at 10% strain, comparing all orientations, aspects, and regions (p = 0.0001). Synthetic grafts are significantly stiffer than aortic and pulmonary homografts at all strain levels (p < 0.046). Aortic, pulmonary artery, and synthetic grafts exhibit hyperelastic biomechanical behavior with anisotropic effect. Differences in mechanical properties among vascular grafts may affect native tissue behavior and ventricular/arterial mechanical coupling, and increase the risk of deformation due to abnormal CHD hemodynamics.

Utility of Cardiovascular Magnetic Resonance-Derived Wave Intensity Analysis As a Marker of Ventricular Function in Children with Heart Failure and Normal Ejection Fraction

OBJECTIVE

This study sought to explore the diagnostic insight of cardiovascular magnetic resonance (CMR)-derived wave intensity analysis to better study systolic dysfunction in young patients with chronic diastolic dysfunction and preserved ejection fraction (EF), comparing it against other echocardiographic and CMR parameters.

BACKGROUND

Evaluating systolic and diastolic dysfunctions in children is challenging, and a gold standard method is currently lacking.

METHODS

Patients with presumed diastolic dysfunction [n = 18; nine aortic stenosis (AS), five hypertrophic, and four restrictive cardiomyopathies] were compared with age-matched control subjects (n = 18). All patients had no mitral or aortic incompetence, significant AS, or reduced systolic EF. E/A ratio, E/E' ratio, deceleration time, and isovolumetric contraction time were assessed on echocardiography, and indexed left atrial volume (LAVi), acceleration time (AT), ejection time (ET), and wave intensity analyses were calculated from CMR. The latter was performed on CMR phase-contrast flow sequences, defining a ratio of the peaks of the early systolic forward compression wave (FCW) and the end-systolic forward expansion wave (FEW).

RESULTS

Significant differences between patients and controls were seen in the E/E' ratio (8.7 ± 4.0 vs. 5.1 ± 1.3, p = 0.001) and FCW/FEW ratio (2.5 ± 1.6 vs. 7.2 ± 4.2 × 10^-5 m/s, p < 0.001), as well as-as expected-LAVi (80.7 ± 22.5 vs. 51.0 ± 10.9 mL/m², p < 0.001). In particular, patients exhibited a lower FCW (2.5 ± 1.6 vs. 7.2 ± 4.2 × 10^-5 m/s, p < 0.001) in the face of preserved EF (67 ± 11 vs. 69 ± 5%, p = 0.392), as well as longer isovolumetric contraction time (49 ± 7 vs. 34 ± 7 ms, p < 0.001) and ET/AT (0.35 ± 0.04 vs. 0.27 ± 0.04, p < 0.001).

CONCLUSION

This study shows that the wave intensity-derived ratio summarizing systolic and diastolic function could provide insight into ventricular function in children, on top of CMR and echocardiography, and it was here able to identify an element of ventricular dysfunction with preserved EF in a small group of young patients.

Feasibility of cardiovascular magnetic resonance derived coronary wave intensity analysis

BACKGROUND

Wave intensity analysis (WIA) of the coronary arteries allows description of the predominant mechanisms influencing coronary flow over the cardiac cycle. The data are traditionally derived from pressure and velocity changes measured invasively in the coronary artery. Cardiovascular magnetic resonance (CMR) allows measurement of coronary velocities using phase velocity mapping and derivation of central aortic pressure from aortic distension. We assessed the feasibility of WIA of the coronary arteries using CMR and compared this to invasive data.

METHODS

CMR scans were undertaken in a serial cohort of patients who had undergone invasive WIA. Velocity maps were acquired in the proximal left anterior descending and proximal right coronary artery using a retrospectively-gated breath-hold spiral phase velocity mapping sequence with high temporal resolution (19 ms). A breath-hold segmented gradient echo sequence was used to acquire through-plane cross sectional area changes in the proximal ascending aorta which were used as a surrogate of an aortic pressure waveform after calibration with brachial blood pressure measured with a sphygmomanometer. CMR-derived aortic pressures and CMR-measured velocities were used to derive wave intensity. The CMR-derived wave intensities were compared to invasive data in 12 coronary arteries (8 left, 4 right). Waves were presented as absolute values and as a % of total wave intensity. Intra-study reproducibility of invasive and non-invasive WIA was assessed using Bland-Altman analysis and the intraclass correlation coefficient (ICC).

RESULTS

The combination of the CMR-derived pressure and velocity data produced the expected pattern of forward and backward compression and expansion waves. The intra-study reproducibility of the CMR derived wave intensities as a % of the total wave intensity (mean ± standard deviation of differences) was 0.0 ± 6.8%, ICC = 0.91. Intra-study reproducibility for the corresponding invasive data was 0.0 ± 4.4%, ICC = 0.96. The invasive and CMR studies showed reasonable correlation (r = 0.73) with a mean difference of 0.0 ± 11.5%.

CONCLUSION

This proof of concept study demonstrated that CMR may be used to perform coronary WIA non-invasively with reasonable reproducibility compared to invasive WIA. The technique potentially allows WIA to be performed in a wider range of patients and pathologies than those who can be studied invasively.

Arterial stiffness and arterial function in adult cyanotic patients with congenital heart disease

BACKGROUND

Mortality in cyanotic patients with congenital heart diseases (CHD) is high, mainly due to cardiovascular complications. It is known that endothelial dysfunction, increased arterial stiffness, and impaired vascular function have negative influence on cardiovascular prognosis. The aim of the study was to assess parameters of arterial stiffness and vascular dysfunction in cyanotic patients with CHD as well as their potential relation to impaired blood oxygen saturation and polycythemia parameters typical for cyanosis.

METHODS

A total of 36 CHD cyanotic patients (17 males) (42.3±16.3 years) and 35 healthy individuals (16 males) (39.6±10.4 years) were enrolled. Assessed parameters were intima media thickness and flow-mediated dilatation (FMD). Assessed parameters using applanation tonometry methods were aortic systolic pressure, aortic pulse pressure (AoPP), augmentation pressure (AP), augmentation index (AI), pulse pressure amplification (PPampl), and pulse wave velocity (PWV).

RESULTS

AoPP (37.3±11.1mmHg vs. 29±6.5mmHg; p=0.002), AP (10.1±7.3mmHg vs. 1.1±3.9mmHg; p=0.00001), AI (24.7±13.5% vs. 3.0±13.6%; p=0.00001), and PWV (7.4±2.1m/s vs. 6.3±0.7m/s; p=0.003) were higher, and PPampl was lower (135.3±16.1% vs. 160.4±12.8%; p=0.00001) in the studied group compared to controls and proved the presence of the increased stiffness of arteries. Impairment of FMD was observed (9.0±5.6 vs. 10.9±4.7; p=0.04). No significant correlations were found between analyzed arterial parameters and biochemical ones characterizing cyanotic patients depicting rheological properties of blood.

CONCLUSIONS

Cyanotic patients with CHD are characterized by increased arterial stiffness estimated with pulse wave analysis parameters and by deteriorated arterial function expressed with worse vasodilatative response in comparison with healthy population. It may confirm relevance of those mechanisms in development of increased rate of cardiovascular events in this population. Association between oxygen saturation or polycythemia and arterial stiffening or vascular dysfunction was not found in these patients.

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.

Clinical-Physiological Considerations in Patients Undergoing Staged Palliation for a Functionally Single Ventricle

OBJECTIVES

The objectives of this review are to discuss the pathophysiology of the circulation with a functionally univentricular heart, with a focus on the unique physiologic characteristics, which provide the underpinnings for the management of these complex patients.

DATA SOURCE

MEDLINE and PubMed.

CONCLUSIONS

The circulation of the patient with a functionally univentricular heart displays unique physiologic characteristics, which are quite different from those of the normal biventricular circulation. There are profound differences within the heart itself in terms of ventricular function, interventricular interactions, and myocardial architecture, which are likely to have significant implications for the efficiency of ventricular ejection and metabolism. The coupling between the systemic ventricle and the aorta also displays unique features. The 3D orientation of the Fontan anastomosis itself can profoundly impact cardiac output, although the "portal" pulmonary arterial bed is a crucial determinant of overall cardiovascular function. As a result, disease-specific approaches to improve cardiovascular function are required at all stages during the care of these complex patients.

Maladaptive aortic properties after the Norwood procedure: An angiographic analysis of the Pediatric Heart Network Single Ventricle Reconstruction Trial

OBJECTIVES

Aortic arch reconstruction in children with single ventricle lesions may predispose to circulatory inefficiency and maladaptive physiology leading to increased myocardial workload. We sought to describe neoaortic anatomy and physiology, risk factors for abnormalities, and impact on right ventricular function in patients with single right ventricle lesions after arch reconstruction.

METHODS

Prestage II aortic angiograms from the Pediatric Heart Network Single Ventricle Reconstruction trial were analyzed to define arch geometry (Romanesque [normal], crenel [elongated], or gothic [angular]), indexed neoaortic dimensions, and distensibility. Comparisons were made with 50 single-ventricle controls without prior arch reconstruction. Factors associated with ascending neoaortic dilation, reduced distensibility, and decreased ventricular function on the 14-month echocardiogram were evaluated using univariate and multivariable logistic regression.

RESULTS

Interpretable angiograms were available for 326 of 389 subjects (84%). Compared with controls, study subjects more often demonstrated abnormal arch geometry (67% vs 22%, P < .01) and had increased ascending neoaortic dilation (Z score 3.8 ± 2.2 vs 2.6 ± 2.0, P < .01) and reduced distensibility index (2.2 ± 1.9 vs 8.0 ± 3.8, P < .01). Adjusted odds of neoaortic dilation were increased in subjects with gothic arch geometry (odds ratio [OR], 3.2 vs crenel geometry, P < .01) and a right ventricle-pulmonary artery shunt (OR, 3.4 vs Blalock-Taussig shunt, P < .01) but were decreased in subjects with aortic atresia (OR, 0.7 vs stenosis, P < .01) and those with recoarctation (OR, 0.3 vs no recoarctation, P = .04). No demographic, anatomic, or surgical factors predicted reduced distensibility. Neither dilation nor distensibility predicted reduced right ventricular function.

CONCLUSIONS

After Norwood surgery, the reconstructed neoaorta demonstrates abnormal anatomy and physiology. Further study is needed to evaluate the longer-term impact of these features.

Vulnerability of Coronary Circulation After Norwood Operation

BACKGROUND

We hypothesized that the myocardial oxygen supply-demand balance is impaired in patients after a Norwood procedure and that an abnormal oxygen supply-demand balance is associated with pronounced activation of the renin-angiotensin-aldosterone system and worse clinical outcome after this procedure.

METHODS

To investigate the myocardial oxygen supply-demand balance, the subendocardial viability ratio (SEVR) was measured in 29 hypoplastic left heart syndrome patients after the Norwood procedure, in 27 patients with pulmonary atresia whose pulmonary blood flow was supplied from the aortopulmonary (AP) shunt, and in 30 control patients who were considered to have normal biventricular circulation. The SEVR in Norwood (0.57 ± 0.18) and AP shunt (0.66 ± 0.10) patients was significantly reduced compared with that in controls (0.94 ± 0.25, p < 0.001 vs Norwood and AP shunt).

RESULTS

After controlling for heart rate, the SEVR was significantly lower in Norwood than in AP shunt patients (p < 0.001). Importantly, the SEVR was significantly lower in Norwood patients with poor clinical outcomes (cardiac arrest before second-stage operation, progressive tricuspid regurgitation, or reduction of ejection fraction <0.35) than in the remaining Norwood patients (0.51 ± 0.12 vs 0.69 ± 0.22, p < 0.01). An SEVR of less than 0.52 had a more than 76% probability of having a poor outcome (p < 0.05). Furthermore, a lower SEVR was significantly correlated with more pronounced renin-angiotensin-aldosterone system activation and elevated natriuretic peptides in serum. Multiple regression analysis revealed that increased aortic stiffness and a smaller neoaorta relative to the native descending aorta were independent determinants of reduced SEVR.

CONCLUSIONS

Myocardial oxygen supply-demand imbalance is intrinsic to Norwood circulation but may be improved by technical refinement of aortic reconstruction or afterload-reducing medication with renin-angiotensin-aldosterone system blockade.

Frequent Dilatation of the Descending Aorta in Children With Hypoplastic Left Heart Syndrome Relates to Decreased Aortic Arch Elasticity

Background

Patients with hypoplastic left heart syndrome after a Norwood operation show dilatation and reduced distensibility of the reconstructed proximal aorta. Cardiac magnetic resonance imaging (CMR) and angiographic examinations indicate that the native descending aorta (DAo) is also dilated, but this has not been studied in detail.

Methods and Results

Seventy‐nine children with hypoplastic left heart syndrome in Fontan circulation (aged 6.3±3.2 years) and 18 control participants (aged 6.8±2.4 years) underwent 3.0‐tesla CMR. Gradient‐echo cine and phase‐contrast imaging was applied to measure cross‐sectional areas (CSAs), distensibility, pulse wave velocity, and the incremental elastic modulus of the thoracic aorta. CSA of the DAo in patients was also compared with published percentiles for aortic CSA. Patients had significantly larger CSA of the DAo at the level of pulmonary artery bifurcation (229.1±97.2 versus 175.7±24.3 mm/m², P=0.04) and the diaphragm (196.2±66.0 versus 142.6±16.7 mm/m², P<0.01). In 41 patients (52%), CSA of the DAo was >95th percentile level for control participants, and the incremental elastic modulus of the aortic arch and the DAo was higher than in patients with normal CSAs (arch: 90.1±64.3 versus 45.6±38.9 m/s; DAo: 86.3±53.7 versus 47.1±47.6 m/s; P<0.01). Incremental elastic modulus of the aortic arch and the DAo correlated with the CSA of the DAo (arch: r=0.5; DAo: r=0.49; P<0.01).

Conclusions

Children with hypoplastic left heart syndrome frequently show dilatation of their DAo associated with increased stiffness of the aortic arch. Higher aortic impedance increases the afterload of the systemic circulation and likely contributes to the burden of the systemic right ventricle.

Comparison by magnetic resonance phase contrast imaging of pulse-wave velocity in patients with single ventricle who have reconstructed aortas versus those without

Pulse-wave velocity (PWV), a measure of arterial stiffness, is a known independent risk factor for cardiovascular events. Patients with single ventricle who undergo aortic to pulmonary anastomosis (recon) have noncompliant patch material inserted into the neoaorta, possibly increasing vessel stiffness and afterload. The purpose of this study is to determine if PWV in patients with single ventricle differed between those who did and those who did not undergo aortic reconstruction (nonrecon). We retrospectively reviewed cardiac magnetic resonance anatomic, cine, and phase contrast evaluations in the ascending aorta and descending aorta (DAo) at the level of the diaphragm data from 126 patients with single ventricle (8.6 ± 8.0 years) from January 2012 to May 2013. Significance = p <0.05. Seventy-five patients underwent recon and 51 did not. PWV in recon was significantly higher than in nonrecon (3.9 ± 0.9 m/s vs 3.2 ± 1.0 m/s, p = 0.008); in recon, patients >13 years old had a higher PWV than those <7 years (4.5 ± 0.6 vs 3.5 ± 0.7 m/s, p = 0.004). Whether <7 or >13 years old, PWV of those with recon was higher than nonrecon DAo distensibility was similar between both groups. There was no difference in age, body surface area, or cardiac index between recon and nonrecon. No correlations between various hemodynamic and ventricular function parameters with PWV were noted. In conclusion, PWV in recon is higher than in nonrecon with similar DAo distensibility implicating the aortic reconstruction as a possible cause of increased afterload; older recon patients have stiffer aortas than younger ones, possibly imposing an additional cardiovascular risk in the future. Other biomaterials may potentially moderate PWV if clinical outcome is adversely affected.

Redefining Expectations of Long-Term Survival After the Fontan Procedure

Background—

The life expectancy of patients undergoing a Fontan procedure is unknown.

Methods and Results—

Follow-up of all 1006 survivors of the 1089 patients who underwent a Fontan procedure in Australia and New Zealand was obtained from a binational population-based registry including all pediatric and adult cardiac centers. There were 203 atriopulmonary connections (AP; 1975–1995), 271 lateral tunnels (1988–2006), and 532 extracardiac conduits (1997–2010). The proportion with hypoplastic left heart syndrome increased from 1/173 (1%) before 1990 to 80/500 (16%) after 2000. Survival at 10 years was 89% (84%–93%) for AP and 97% (95% confidence interval [CI], 94%–99%) for lateral tunnels and extracardiac conduits. The longest survival estimate was 76% (95% CI, 67%–82%) at 25 years for AP. AP independently predicted worse survival compared with extracardiac conduits (hazard ratio, 6.2; P <0.001; 95% CI, 2.4–16.0). Freedom from failure (death, transplantation, takedown, conversion to extracardiac conduits, New York Heart Association III/IV, or protein-losing enteropathy/plastic bronchitis) 20 years after Fontan was 70% (95% CI, 63%–76%). Hypoplastic left heart syndrome was the primary predictor of Fontan failure (hazard ratio, 3.8; P <0.001; 95% CI, 2.0–7.1). Ten-year freedom from failure was 79% (95% CI, 61%–89%) for hypoplastic left heart syndrome versus 92% (95% CI, 87%–95%) for other morphologies.

Conclusions—

The long-term survival of the Australia and New Zealand Fontan population is excellent. Patients with an AP Fontan experience survival of 76% at 25 years. Technical modifications have further improved survival. Patients with hypoplastic left heart syndrome are at higher risk of failure. Large, comprehensive registries such as this will further improve our understanding of late outcomes after the Fontan procedure.

Aortic stiffness and left ventricular diastolic function in children following early repair of aortic coarctation

Aortic stiffness and diastolic function are abnormal in adults with repaired coarctation of the aorta (CoA). The goal of this study was to determine the relation between aortic stiffness and left ventricular (LV) diastolic impairment in children who had undergone CoA repair very early in life. This is a retrospective review of echocardiograms in children with isolated repaired CoA (group CoA; n = 24) and healthy matched controls (group Normal; n = 24). We analyzed systolic and LV diastolic functions, proximal and distal ascending aortic stiffness indices (SIs), distensibility, and strain. Age range was 0.3 to 21 (median 9) years. Age at time of CoA repair was 0 to 24 (median 0.5) months. Median time since CoA repair was 6 years. There was no significant difference in blood pressure, LV size, and systolic function between the groups. LV diastolic function was impaired in group CoA compared with group Normal (septal E': CoA 10.3 ± 1.6 cm/s and Normal 13.4 ± 1.9 cm/s, p <0.001). All parameters of proximal and distal ascending aortic elasticities were abnormal in group CoA versus Normal (SI of proximal ascending aorta: CoA 4.9 ± 1.6 and Normal 2.7 ± 0.6, p <0.001). Across all patients, there was a strong correlation between septal E' and proximal ascending aortic SI (r = -0.72, p <0.001). In conclusion, even children who underwent CoA repair at a very young age have abnormal LV diastolic function and aortic elasticity compared with controls and there is a linear relation between the 2. LV diastolic dysfunction in patients with repaired CoA may be due to chronically increased afterload.

Aortopulmonary collateral flow is related to pulmonary artery size and affects ventricular dimensions in patients after the fontan procedure

BACKGROUND

Aortopulmonary collaterals (APCs) are frequently found in patients with a single-ventricle (SV) circulation. However, knowledge about the clinical significance of the systemic-to-pulmonary shunt flow in patients after the modified Fontan procedure and its potential causes is limited. Accordingly, the aim of our study was to detect and quantify APC flow using cardiovascular magnetic resonance (CMR) and assess its impact on SV volume and function as well as to evaluate the role of the size of the pulmonary arteries in regard to the development of APCs.

METHODS

60 patients (mean age 13.3 ± 6.8 years) after the Fontan procedure without patent tunnel fenestration underwent CMR as part of their routine clinical assessment that included ventricular functional analysis and flow measurements in the inferior vena cava (IVC), superior vena cava (SVC) and ascending aorta (Ao). APC flow was quantified using the systemic flow estimator: (Ao) - (IVC + SVC). Pulmonary artery index (Nakata index) was calculated as RPA + LPA area/body surface area using contrast enhanced MR angiography. The patient cohort was divided into two groups according to the median APC flow: group 1 < 0.495 l/min/m(2) and group 2 > 0.495 l/min/m(2).

RESULTS

Group 1 patients had significant smaller SV enddiastolic (71 ± 16 vs 87 ± 25 ml/m(2); p=0.004) and endsystolic volumes (29 ± 11 vs 40 ± 21 ml/m(2); p=0.02) whereas ejection fraction (59 ± 9 vs 56 ± 13%; p=0.38) differed not significantly. Interestingly, pulmonary artery size showed a significant inverse correlation with APC flow (r=-0.50, p=0.002).

CONCLUSIONS

Volume load due to APC flow in Fontan patients affected SV dimensions, but did not result in an impairment of SV function. APC flow was related to small pulmonary artery size, suggesting that small pulmonary arteries represent a potential stimulus for the development of APCs.

Modeling single ventricle physiology: review of engineering tools to study first stage palliation of hypoplastic left heart syndrome

First stage palliation of hypoplastic left heart syndrome, i.e., the Norwood operation, results in a complex physiological arrangement, involving different shunting options (modified Blalock-Taussig, RV-PA conduit, central shunt from the ascending aorta) and enlargement of the hypoplastic ascending aorta. Engineering techniques, both computational and experimental, can aid in the understanding of the Norwood physiology and their correct implementation can potentially lead to refinement of the decision-making process, by means of patient-specific simulations. This paper presents some of the available tools that can corroborate clinical evidence by providing detailed insight into the fluid dynamics of the Norwood circulation as well as alternative surgical scenarios (i.e., virtual surgery). Patient-specific anatomies can be manufactured by means of rapid prototyping and such models can be inserted in experimental set-ups (mock circulatory loops) that can provide a valuable source of validation data as well as hydrodynamic information. Such models can be tuned to respond to differing the patient physiologies. Experimental set-ups can also be compatible with visualization techniques, like particle image velocimetry and cardiovascular magnetic resonance, further adding to the knowledge of the local fluid dynamics. Multi-scale computational models include detailed three-dimensional (3D) anatomical information coupled to a lumped parameter network representing the remainder of the circulation. These models output both overall hemodynamic parameters while also enabling to investigate the local fluid dynamics of the aortic arch or the shunt. As an alternative, pure lumped parameter models can also be employed to model Stage 1 palliation, taking advantage of a much lower computational cost, albeit missing the 3D anatomical component. Finally, analytical techniques, such as wave intensity analysis, can be employed to study the Norwood physiology, providing a mechanistic perspective on the ventriculo-arterial coupling for this specific surgical scenario.