Management of the postoperative Fontan patient

Visual liver assessment using Gd-EOB-DTPA-enhanced magnetic resonance imaging of patients in the early post-Fontan period

No imaging modality can be used to evaluate Fontan-associated liver disease (FALD). We retrospectively reviewed hepatic gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging (EOB-MRI) characteristics of patients within 1 year post-Fontan procedure, and we evaluated the association between hepatic imaging abnormalities and clinical parameters, including follow-up cardiac catheterization and laboratory test findings. The EOB-MR images were graded, based on the extent of the decreased enhancement, as “normal” (Grade 1), “segmental” (Grade 2), “regional” (Grade 3), and “diffuse” (Grade 4). We enrolled 37 patients (mean age, 3.5 ± 1.0 years): 9 patients had Grade 1 or 2; 14 patients, Grade 3; and 14 patients, Grade 4. EOB-MRI revealed characteristic reticular or mosaic patterns of diminished enhancement (i.e. “frog spawn” appearance). Ultrasonography did not detect diminished enhancement or “frog spawn” appearance. A trend existed toward increased grade severity in imaging with increased central venous pressure, pulmonary vascular resistance, and gamma-glutamyltransferase levels. Noninvasive EOB-MRI revealed the characteristic pattern of diminished enhancement, which was correlated with certain clinical parameters indicative of Fontan physiology and liver dysfunction. Early-stage FALD may occur soon after the Fontan procedure and is associated with increased pressure in the inferior vena cava and hepatic veins.

Relationship of single ventricle filling and preload to total cavopulmonary connection hemodynamics

BACKGROUND

Single ventricle lesions are associated with gradual attrition after surgical palliation with the total cavopulmonary connection (TCPC). Ventricular dysfunction is frequently noted, particularly impaired diastolic performance. This study seeks to relate TCPC hemodynamic energy losses to single ventricle volumes and filling characteristics.

METHODS

Cardiac magnetic resonance (CMR) data were retrospectively analyzed for 30 single ventricle patients at an average age of 12.7 ± 4.8 years. Cine ventricular short-axis scans were semiautomatically segmented for all cardiac phases. Ventricular volumes, ejection fraction, peak filling rate, peak ejection rate, and time to peak filling were calculated. Corresponding patient-specific TCPC geometry was acquired from a stack of transverse CMR images; relevant flow rates were segmented from through-plane phase contrast CMR data at TCPC inlets and outlets. The TCPC indexed power loss was calculated from computational fluid dynamics simulations using a validated custom solver. Time-averaged flow conditions and rigid vessel walls were assumed in all cases. Pearson correlations were used to detect relationships between variables, with p less than 0.05 considered significant.

RESULTS

Ventricular end-diastolic (R = -0.48) and stroke volumes (R = -0.37) had significant negative correlations with the natural logarithm of a flow-independent measure of power loss. This power loss measure also had a significant positive relationship to time to peak filling rate (normalized to cycle time; R = 0.67).

CONCLUSIONS

Flow-independent TCPC power loss is inversely related with ventricular end-diastolic and stroke volumes. Elevated power losses may contribute to impaired diastolic filling and limited preload reserve in single ventricle patients.

Fontan hemodynamics from 100 patient-specific cardiac magnetic resonance studies: a computational fluid dynamics analysis

OBJECTIVES

This study sought to quantify average hemodynamic metrics of the Fontan connection as reference for future investigations, compare connection types (intra-atrial vs extracardiac), and identify functional correlates using computational fluid dynamics in a large patient-specific cohort. Fontan hemodynamics, particularly power losses, are hypothesized to vary considerably among patients with a single ventricle and adversely affect systemic hemodynamics and ventricular function if suboptimal.

METHODS

Fontan connection models were created from cardiac magnetic resonance scans for 100 patients. Phase velocity cardiac magnetic resonance in the aorta, vena cavae, and pulmonary arteries was used to prescribe patient-specific time-averaged flow boundary conditions for computational fluid dynamics with a customized, validated solver. Comparison with 4-dimensional cardiac magnetic resonance velocity data from selected patients was used to provide additional verification of simulations. Indexed Fontan power loss, connection resistance, and hepatic flow distribution were quantified and correlated with systemic patient characteristics.

RESULTS

Indexed power loss varied by 2 orders of magnitude, whereas, on average, Fontan resistance was 15% to 20% of published values of pulmonary vascular resistance in single ventricles. A significant inverse relationship was observed between indexed power loss and both systemic venous flow and cardiac index. Comparison by connection type showed no differences between intra-atrial and extracardiac connections. Instead, the least efficient connections revealed adverse consequences from localized Fontan pathway stenosis.

CONCLUSIONS

Fontan power loss varies from patient to patient, and elevated levels are correlated with lower systemic flow and cardiac index. Fontan connection type does not influence hemodynamic efficiency, but an undersized or stenosed Fontan pathway or pulmonary arteries can be highly dissipative.

Long-term management of patients with hypoplastic left heart syndrome: the diagnostic approach at All Children's Hospital

Improved survival in children with hypoplastic left heart syndrome has created a sub-population of children and young adults who are living with functionally univentricular physiology. Routine surveillance with comprehensive screening for structural cardiac disease, functional cardiac disease, arrhythmias, thromboembolic disease, and associated dysfunction of end organs is important. Future directives will better define the plans of care for routine surveillance in patients with hypoplastic left heart syndrome.

The Fontan circulation and right parietal craniotomy for seizures: the challenges of adult congenital heart disease

The management of a patient who had previously undergone surgical palliation of tricuspid atresia at the age of two, and who required right parietal craniotomy for resection of seizure focus, is presented. The anesthetic considerations in patients with Fontan physiology are also presented, as well as the impact on patients undergoing neurosurgical procedures, specifically, craniotomy for seizure focus resection. The physiologic demands of modern surgical practice requires that there is a thorough understanding of the complex circulations that exist in patients with congenital heart disease.

Introduction of a New Optimized Total Cavopulmonary Connection

BACKGROUND

Several variations of the total cavopulmonary connection (TCPC) have been investigated for favorable fluid mechanics and flow distribution. This study presents a hemodynamically optimized TCPC configuration code-named "OptiFlo." Featuring bifurcated vena cava (superior venacava to inferior vena cava SVC/IVC), it was designed to lower the fluid mechanical power losses in the connection and to ensure proper hepatic blood perfusion to both lungs.

METHODS

A rapid prototype model of the OptiFlo TCPC was built and in vitro control volume flow analysis was performed to evaluate the fluid mechanical power loss performance of the model. Furthermore, computational fluid dynamics simulations were used to investigate the flow patterns in the model, which were compared with those in the planar one-diameter offset TCPC with flared anastomosis sites, the best known TCPC configuration to date.

RESULTS

Compared with the one-diameter offset reference model, the OptiFlo showed lower power losses: -26%, -31%, and -42% for increasing cardiac outputs of 2, 4, and 6 L/minute, respectively. No statistically significant differences were found in power loss between 40:60 and 50:50 SVC/IVC flow ratios (p > 0.1) for the OptiFlo model. The power loss characteristic curve for different left and right pulmonary artery ratios was flatter for the OptiFlo than the one-diameter offset reference model. Pulmonary artery flow was much more streamlined in the OptiFlo compared with the one-diameter offset model.

CONCLUSIONS

The OptiFlo TCPC design exhibits lower power losses with better adaptive distribution of hepatic blood to both lungs and lower blood flow disturbances compared with the planar one-diameter offset TCPC model. Its significantly superior hemodynamic performance at higher cardiac outputs (exercise) rationalizes further design and feasibility studies toward a workable clinical model.

Flow study of an extracardiac connection with persistent left superior vena cava

BACKGROUND

Numerous studies have sought to optimize the design of total cavopulmonary connections with a single superior vena cava. This study was directed to the 2% to 4.5% of the population with dual superior venae cavae, investigating the flow fields associated with such total cavopulmonary connection anatomies. Additionally, it demonstrates the potential use of computational designs and simulations as surgical planning tools.

METHODS

A 3-dimensional model of a total cavopulmonary connection with bilateral superior venae cavae was reconstructed from a patient's magnetic resonance images and investigated experimentally and numerically to assess the power losses and flow structures within the connection. On the basis of these results, a virtual operation was performed in the computer to improve the original connection design. The modified anatomy was studied numerically.

RESULTS

Because of a smooth connection with an extracardiac conduit and no major dimension mismatch between the baffle and the connecting vessels, the original anatomy yielded smooth flow fields, low power losses, and few disturbances. However, a large offset between the inferior vena cava and the left superior vena cava resulted in flow stasis and unbalanced hepatic flow distribution. Shifting the inferior vena cava and positioning it between the 2 superior venae cavae resulted in a 7% decrease in power losses and eliminated the associated flow stasis regions in the main pulmonary artery segment.

CONCLUSIONS

This study demonstrates the potential use of computer-aided design and numeric simulations for surgical planning. It shows that locating the inferior vena cava between the superior venae cavae may lead to better-balanced lung perfusion. This may require suturing the right and left superior venae cavae closer to each other during the hemi-Fontan or Glenn stage.

Coupling Pediatric Ventricle Assist Devices to the Fontan Circulation: Simulations with a Lumped-Parameter Model

In pediatric ventricular assist device (VAD) design, the process of matching device characteristics and dimensions to the relevant disease conditions poses a formidable challenge because the disease spectrum is more highly varied than for adult applications. One example arises with single-ventricle congenital defects, which demand palliative surgeries that create elevated systemic venous pressure and altered pulmonary hemodynamics. Substituting a mechanical pump as a right ventricle has long been proposed to eliminate the associated early and postoperative anomalies. A pulsatile lumped-parameter model of the single-ventricle circulation was developed to guide the preliminary design studies. Two special modules, the pump characteristics and the total cavopulmonary connection (TCPC) module, are introduced. The TCPC module incorporates the results of three-dimensional patient-specific computational fluid dynamics calculations, where the pressure drop in the TCPC anastomosis is calculated at the equal vascular lung resistance operating point for different cardiac outputs at a steady 60/40 inferior vena cava/superior vena cava flow split. Preliminary results obtained with the adult parameters are presented with no ventricle remodeling or combined larger-size single ventricle. A detailed literature review of single-ventricle function is provided. Coupling a continuous pump to the single-ventricle circulation brought both the pulmonary and systemic venous pressures back to manageable levels. Selected VADs provided an acceptable cardiac output trace of the single left ventricle, after initial transients. Remodeling of the systemic venous compliance plays a critical role in performance and is included in this study. Pulsatile operation mode with rotational speed regulation highlighted the importance of TCPC and pulmonary artery compliances. Four different pumps and three patient-specific anatomical TCPC pathologies were studied. Magnitudes of the equivalent TCPC resistances were found to be comparable to the vascular resistances of the normal baseline circulation, significantly affecting both the VAD design and hemodynamics.

In Vitro Flow Analysis of a Patient-Specific Intraatrial Total Cavopulmonary Connection

BACKGROUND

Understanding the hemodynamics of the total cavopulmonary connection may lead to further optimization of the connection design and surgical planning, which in turn may lead to improved surgical outcome. Although most experimental and numerical investigations have mainly focused on somewhat simplified geometries, investigation of the flow field of true anatomic configurations is necessary for a true understanding.

METHODS

An intraatrial connection was reconstructed from patient magnetic resonance images and manufactured using transparent stereolithography. Power loss, flow visualization, and digital particle image velocimetry as well as computational fluid dynamics simulations were performed to characterize the anatomic flow structure. Given the complexity of the anatomic flow, two simplified versions of the geometry were manufactured and run through power loss and flow visualization studies.

RESULTS

Experimental measurements revealed complex, unsteady, and highly three-dimensional flow structures within the anatomic model, leading to high pressure drops and power losses. The small vessel diameters were the primary cause of these losses. Numerical simulations demonstrated that most of the dissipation occurred in the pulmonary arteries. Finally, asymmetric pulmonary diameters together with the bulgy intraatrial connection favored the rise of flow unsteadiness and unbalanced lung perfusion.

CONCLUSIONS

The technique developed in this study enabled a deeper understanding of the hemodynamics behind an intraatrial connection. Future endeavors would be to study variation among differing surgical techniques, comparing intraatrial and extracardiac approaches.