Aortopulmonary Collateral Flow Research Articles

Abstract 17257: Aortopulmonary Collateral Burden in the Fontan Circulation: Longitudinal Changes and Relationship With Clinical Outcomes

Background: Aortopulmonary collaterals (APC) are a common source of volume load in patients with a Fontan circulation and their burden can be quantified by CMR. Longitudinal trends in APC flow and their relationship with outcomes have not been described. Hypothesis: Higher APC flow will be associated with worse clinical outcomes in Fontan patients. Aims: To assess longitudinal changes in APC flow in the Fontan circulation using CMR and their relationship with outcomes. Methods: Single-center retrospective analysis of Fontan patients who had at least 1 CMR with APC flow data. APC flow was estimated as the difference between aortic and systemic venous flows and also expressed as a percent of aortic flow. Primary outcome was a composite of death or heart transplantation; secondary outcomes included protein losing enteropathy, ascites, chylothorax, and hemoptysis. The baseline (time at Fontan=time 0) and trend in APC flow were estimated using a linear mixed model with a random intercept and slope for each patient. Results: Analysis included 758 CMRs from 356 patients; 123 of whom had ≥ 2 CMRs. Median age at first CMR was 14 y (IQR 10-19 y) and median CMRs per patient were 2 (range 1-12). Baseline APC flow was 0.6 (±0.5) L/min/m 2 or 17 (±10) % of aortic flow. Increasing APC flow over time correlated with increasing trend in ventricular dilation and decreasing trend in SaO 2 . Over a median follow-up of 17 years, 22 patients (6%) had the composite outcome. High baseline APC flow as well as an increasing trend in APC flow were associated with clinical outcomes including an independent association with death or heart transplantation (Table). Conclusions: APCs represent a significant hemodynamic burden in functional single ventricle hearts palliated to the Fontan circulation. Higher and increasing APC flow is associated with worse clinical outcomes. Factors contributing to APC development and whether APC occlusion results in a lasting reduction in the burden remain to be elucidated.

Cerebral Blood Flow, Brain Injury, and Aortic-Pulmonary Collateral Flow After the Fontan Operation

Patients with a single ventricle develop aortopulmonary collaterals (APCs) whose flow has been shown to be inversely proportional to cerebral blood flow (CBF) in a previous cross-sectional study. Longitudinal CBF and APC flow in patients with Fontan physiology adjusting for brain injury (BI) has never been reported. Decreased CBF and BI may adversely impact neurodevelopment. A prospective longitudinal cohort of 27 patients with Fontan physiology (aged 10 ± 1.9years, 74% male) underwent cardiac and brain magnetic resonance imaging 3 to 9months and 6.0 ± 1.86years after Fontan operation to measure the CBF and APC flow and to reassess the BI (focal BI, generalized insult, and hemorrhage). CBF was measured using jugular venous flow and APC flow was measured by the difference between aortic flow and caval return. Multivariate modeling was used to assess the relation between the change in APC flow and BI. A strong inverse relation was found between CBF/aortic flow change and APC flow/aortic flow and APC flow/body surface area change (R2=0.70 and 0.72 respectively, p <0.02). Overall, the CBF decreased by 9 ± 11% and the APC flow decreased by 0.73 ± 0.67l/min/m2. The evolution of CBF and APC flow were significantly and inversely related when adjusting for time since Fontan operation, gender, and BI on the multivariate modeling. Every unit increase in APC flow change was associated with an 8% decrease in CBF change. In conclusion, CBF and APC flow change are inversely related across serial imaging, adjusting for time from Fontan operation, gender, and BI. CBF and APC aortic flow decrease over a 6-year period. This may adversely impact neurodevelopment. Because APCs can be embolized, this may be a modifiable risk factor. Clinical trials numbers: NCT02135081 and NCT02919956.

Severe aortopulmonary collaterals are associated with lower transplant-free survival in patients undergoing staged single ventricle palliation

ObjectiveTo identify risk factors for aortopulmonary collateral (APC) development and assess the impact of severe APCs in children undergoing staged single ventricle palliation. MethodsChildren undergoing a bidirectional Glenn operation between January 1, 2016, and March 31, 2021, at our center were included. All underwent angiography prior to Glenn and Fontan; APC flow was graded on a scale of 0 (no appreciable collateral flow) to 4 (severe burden). Demographic data, congenital diagnosis, clinical history, and outcomes were stratified by Glenn assessment; Fontan outcomes were stratified by pre-Fontan grade. ResultsSixty patients met the inclusion criteria, all of whom had angiographic evidence of APCs. There were 7 transplants and 9 deaths in the cohort. There were no significant differences in demographics among the patients. Right ventricular morphology was more common in patients with severe pre-Glenn collaterals (24 of 44 vs 2 of 6 vs 7 of 8; P = .014). Longer stage 1 aortic cross-clamp duration was associated with greater severity pre-Glenn (44 minutes vs 34 minutes vs 66 minutes; P = .023). Patients with grade 3 pre-Glenn collaterals more commonly required transplantation than those with grade 1 collaterals (P < .001) and had lower overall transplant-free survival than those with grade 1 (P = .005) or grade 2 (P = .04) collaterals. ConclusionsThe ubiquity of APCs in this study demonstrates their prevalence in single ventricle disease. Right ventricular morphology and prolonged aortic cross-clamp duration are associated with higher burden. Greater severity was associated with decreased transplant-free survival. These data emphasize the negative long-term impact of these collaterals.

Pre-Glenn aorto-pulmonary collaterals in single-ventricle patients.

In single-ventricle patients undergoing staged-bidirectional Glenn, 36-59% have aorto-pulmonary collateral flow, but risk factors and clinical outcomes are unknown. We hypothesise that shunt type and catheter haemodynamics may predict pre-bidirectional Glenn aorto-pulmonary collateral burden, which may predict death/transplantation, pulmonary artery or aorto-pulmonary collateral intervention. Retrospective cohort study of patients undergoing a Norwood procedure for single-ventricle anatomy. Covariates included clinical and haemodynamic characteristics up to/including pre-bidirectional Glenn catheterisation and aorto-pulmonary collateral burden at pre-bidirectional Glenn catheterisation. Multivariable models used to evaluate relationships between risk factors and outcomes. From January 2011 to March 2016, 104 patients underwent Norwood intervention. Male sex (odds ratio 3.36, 95% confidence interval 1.17-11.4), age at pre-bidirectional Glenn assessment (2.12, 1.33-3.39 per month), and pulmonary to systemic flow ratio (1.23, 1.08-1.41 per 0.1 unit) were associated with aorto-pulmonary collateral burden. Aorto-pulmonary collateral burden was not associated with death/transplantation (hazard ratio 1.19, 95% confidence interval 0.37-3.85), pulmonary artery (sub-hazard ratio 1.38, 0.32-2.61), or aorto-pulmonary collateral interventions (sub-hazard ratio 1.11, 0.21-5.76). Longer post-Norwood length of stay was associated with greater risk of death/transplantation (hazard ratio 1.22 per week, 95% confidence interval 1.08-1.38), but lower risk of aorto-pulmonary collateral intervention (sub-hazard ratio 0.86 per week, 95% confidence interval 0.75-0.98). Time to pre-bidirectional Glenn catheterisation was associated with lower risk of pulmonary artery (sub-hazard ratio 0.80 per month, 95% confidence interval 0.65-0.98) and aorto-pulmonary collateral intervention (sub-hazard ratio 0.79, 0.63-0.99). Probability of moderate/severe aorto-pulmonary collateral burden increased with left-to-right shunt (22.5% at <1.0, 57.6% at >1.4) and the age at pre-bidirectional Glenn catheterisation (10.6% at <2 months, 56.9% at >5 months). Aorto-pulmonary collateral burden is common after Norwood procedure and increases as age at bidirectional Glenn increases. As expected, higher pulmonary to systemic flow ratio is a marker for greater aorto-pulmonary collateral burden pre-bi-directional Glenn; aorto-pulmonary collateral burden does not confer risk of death/transplantation or pulmonary artery intervention.

Abstract 11006: Fick’s versus Cardiac MRI Measured Pulmonary Blood Flow in Pre-Fontan Assessment

Background: Fick’s principle (FP) is unreliable if there are two sources of pulmonary blood flow (Q p ) with different saturations. We compared Q p and pulmonary vascular resistance (PVRI) measured by cardiac MRI (CMR) and FP in pre-Fontan patients. Material and Methods: Retrospective analysis of CMR and catheterization data obtained under the same general anesthetic from Jan 2009 to March 2021. FP derived Q p and PVRI used assumed O 2 consumption from Sackler’s equation. Paired T test was used for comparison between FP and CMR parameters. Results: 98 patients, with (mean ± sd): age 3.01±1.38 years and weight 13.31±2.4 kg. The FP derived Q p was 2.5(± 0.58) L/min/m 2 and PVRI1.91±0.61 Woods units*m 2 (WU*m 2 ). CMR measured pulmonary arterial flow (Q pa ) and pulmonary venous flow (Q pv ) were 1.97±0.55 L/min/m 2 and 3.49±0.76 L/min/m 2 , respectively. The PVRI using CMR Q pv was 1.38±0.47 WU*m 2 . The paired mean differences between Q p by FP and CMR Q pa or CMR Q pv were 0.53 (95%CI 0.41, 0.66; p&lt;0.001) and -0.98(95%CI -1.13, -0.83; p&lt;0.001), respectively. The paired mean difference between PVRI by FP and PVRI by CMR Qpv was 0.53(95%CI 0.44, 0.61; p&lt;0.001). The difference between CMR Q pv and FP derived Q p were correlated with aortopulmonary collateral flow (Pearson r=0.615, p&lt;0.001). PVRI derived from FP (1.91±0.61 WU*m 2 ) was higher than that from CMR (1.38±0.47, p&lt;0.001). However, this only resulted in one FP based PVRI estimate being &gt;4.0WU*m 2 when the CMR PVRI was &lt;4.0WU*m 2 . Conclusion: s: FP derived Q p is lower than CMR Q pv resulting in higher PVRI estimates by FP. In most patients this will not affect clinical risk stratification based on PVRI. In high-risk candidates for the Fontan, CMR based flow measurements are preferrable.

Clinical Variables Associated with Pre-Fontan Aortopulmonary Collateral Burden.

Aortopulmonary collaterals (APCs) develop universally, but to varying degrees, in patients with single ventricle congenital heart disease (CHD). Despite their ubiquitous presence, APCs remain poorly understood. We sought to evaluate the association between APC burden and common non-invasive clinical variables. We conducted a single center, retrospective study of patients with single ventricle CHD and previous Glenn palliation who underwent pre-Fontan cardiac magnetic resonance (CMR) imaging from 3/2018 to 3/2021. CMR was used to quantify APC flow, which was normalized to aortic (APC/QAo) and pulmonary vein (APC/QPV) blood flow. Univariate, multivariable, and classification and regression tree (CART) analyses were done to investigate the potential relationship between CMR-quantified APC burden and clinical variables. A total of 29 patients were included, all of whom had increased APC flow (APC/QAo: 26.9, [22.0, 39.1]%; APC/QPV: 39.4 [33.3, 46.9]%), but to varying degrees (APC/QAo: range 11.9-44.4%; APC/QPV: range 17.7-60.0%). Pulmonary artery size (Nakata index, at pre-Fontan CMR) was the only variable associated with APC flow on multivariable analysis (APC/QAo: p = 0.020, R2 = 0.19; APC/QPV: p = 0.0006, R2 = 0.36) and was the most important variable associated with APC burden identified by CART analysis (size inversely related to APC flow). APC flow is universally increased but highly variable in patients with single ventricle CHD and Glenn circulation. Small branch pulmonary artery size is a key factor associated with increased APC burden; however, the pathogenesis of APCs is likely multifactorial. Further research is needed to better understand APC pathogenesis, including predisposing and mitigating factors.

Mechanical support for the failing single ventricle after Fontan

Mechanical support for the failing single ventricle after Fontan

Exercise-dependent changes in ventricular-arterial coupling and aortopulmonary collateral flow in Fontan patients: a real-time CMR study.

Inefficient ventricular-arterial (V-A) coupling has been described in Fontan patients and may result in adverse haemodynamics. A varying amount of aortopulmonary collateral (APC) flow is also frequently present that increases volume load of the single ventricle. The aim of the study was to assess changes in V-A coupling and APC flow during exercise CMR. Eighteen Fontan patients (age 24 ± 3 years) and 14 controls (age 23 ± 4 years) underwent exercise CMR using a cycle ergometer. Ventricular volumetry and flow measurements in the ascending aorta (AAO), inferior (IVC), and superior (SVC) vena cava were assessed using real-time sequences during stepwise increases in work load. Measures of systemic arterial elastance Ea, ventricular elastance Ees, and V-A coupling (Ea/Ees) were assessed. APC flow was quantified as AAO - (SVC + IVC). Ea remained unchanged during all levels of exercise in both groups (P = 0.39 and P = 0.11). Ees increased in both groups (P = 0.001 and P < 0.001) with exercise but was lower in the Fontan group (P = 0.04). V-A coupling was impaired in Fontan patients at baseline (P = 0.04). Despite improvement during exercise (P = 0.002) V-A coupling remained impaired compared with controls (P = 0.001). Absolute APC flow in Fontan patients did not change during exercise even at maximum work load (P = 0.98). Inefficient V-A coupling was already present at rest in Fontan patients and aggravated during exercise due to a limited increase in ventricular contractility which demonstrates the importance of a limited functional reserve of the single ventricle. APC flow remained unchanged suggesting no further increase in volume load during exercise.

Abstract 12078: Pre-Glenn Aorto-Pulmonary Collaterals and Its Impact on Outcomes in Single Ventricle Patients

Introduction: In single-ventricle patients undergoing bi-directional Glenn (BDG), 36-59% have angiographically detectable aorto-pulmonary collateral (APC) flow. However, predictors, hemodynamic and clinical outcomes are unknown. Hypothesis: We hypothesize that (a) shunt type, hemodynamic findings at the pre-Glenn catheterization predict pre-BDG APC burden and (b) APC burden at BDG catheterization may predict post BDG death/transplantation, pulmonary artery (PA) or APC intervention. Methods: Retrospective cohort study of patients following Norwood Procedure for single ventricle anatomy. Covariates included demographics; clinical and hemodynamic at Pre-BDG catheterization. APC burden at pre-BDG catheterization was assessed dichotomously by a single reader (moderate/severe vs. none/mild). Logistic regression was used to identify predictors of APC burden and Cox regression for time to clinical outcomes. Results: Among 104 patients, 89.4% (n=93/104) underwent pre-BDG catherization, of which 55% (n=51/93) had APC intervention and 91% (n=85/93) progressed to BDG. Post-BDG, 60% (n=51/85) had no/mild and 40% (n=34/85) had moderate/severe APC burden. Within 36 months, APC intervention occurred in 74% (n=69/63) with no difference between groups (84% vs. 79%, Logrank 0.75). Predictors of APC burden were male sex (OR 3.59; 95% CI 1.18-10.98), older age at BDG (1.02 per year; 1.01-1.04), PA saturations (1.80;1.18-2.75), and Qp:Qs ratio (OR 1.23 per 0.10 unit increase;1.08-1.41). APC burden is not predictive of death/transplantation or future APC intervention but may show a trend towards future PA intervention (HR 2.11, 95% CI 0.98-4.52, p=0.056)(Figure 1). Sano shunt is a predictor of APC intervention following BDG (HR 2.07, 95%CI 1.09-3.90, p=0.03). Conclusions: Moderate or severe APC burden was present in 40% after stage I Norwood and QP:QS is a strong predictor for APC burden; patients with moderate/severe APC’s may be at higher risk of PA interventions.

Adverse fibrosis remodeling and aortopulmonary collateral flow are associated with poor Fontan outcomes

BackgroundThe extent and significance in of cardiac remodeling in Fontan patients are unclear and were the subject of this study.MethodsThis retrospective cohort study compared cardiovascular magnetic resonance (CMR) imaging markers of cardiac function, myocardial fibrosis, and hemodynamics in young Fontan patients to controls.ResultsFifty-five Fontan patients and 44 healthy controls were included (median age 14 years (range 7–17 years) vs 13 years (range 4–14 years), p = 0.057). Fontan patients had a higher indexed end-diastolic ventricular volume (EDVI 129 ml/m2 vs 93 ml/m2, p < 0.001), and lower ejection fraction (EF 45% vs 58%, p < 0.001), circumferential (CS − 23.5% vs − 30.8%, p < 0.001), radial (6.4% vs 8.2%, p < 0.001), and longitudinal strain (− 13.3% vs − 24.8%, p < 0.001). Compared to healthy controls, Fontan patients had higher extracellular volume fraction (ECV) (26.3% vs 20.6%, p < 0.001) and native T1 (1041 ms vs 986 ms, p < 0.001). Patients with a dominant right ventricle demonstrated larger ventricles (EDVI 146 ml/m2 vs 120 ml/m2, p = 0.03), lower EF (41% vs 47%, p = 0.008), worse CS (− 20.1% vs − 25.6%, p = 0.003), and a trend towards higher ECV (28.3% versus 24.1%, p = 0.09). Worse EF and CS correlated with longer cumulative bypass (R = − 0.36, p = 0.003 and R = 0.46, p < 0.001), cross-clamp (R = − 0.41, p = 0.001 and R = 0.40, p = 0.003) and circulatory arrest times (R = − 0.42, p < 0.001 and R = 0.27, p = 0.03). T1 correlated with aortopulmonary collateral (APC) flow (R = 0.36, p = 0.009) which, in the linear regression model, was independent of ventricular morphology (p = 0.9) and EDVI (p = 0.2). The composite outcome (cardiac readmission, cardiac reintervention, Fontan failure or any clinically significant arrhythmia) was associated with increased native T1 (1063 ms vs 1026 ms, p = 0.029) and EDVI (146 ml/m2 vs 118 ml/m2, p = 0.013), as well as decreased EF (42% vs 46%, p = 0.045) and worse CS (− 22% vs − 25%, p = 0.029). APC flow (HR 5.5 CI 1.9–16.2, p = 0.002) was independently associated with the composite outcome, independent of ventricular morphology (HR 0.71 CI 0.30–1.69 p = 0.44) and T1 (HR1.006 CI 1.0–1.13, p = 0.07).ConclusionsPediatric Fontan patients have ventricular dysfunction, altered myocardial mechanics and increased fibrotic remodeling. Cumulative exposure to cardiopulmonary bypass and increased aortopulmonary collateral flow are associated with myocardial dysfunction and fibrosis. Cardiac dysfunction, fibrosis, and collateral flow are associated with adverse outcomes.

Flow profile characteristics in Fontan circulation are associated with the single ventricle dilation and function: principal component analysis study.

The Fontan circulation is characterized as a nonpulsatile flow propagation without a pressure-generating ventricle. However, flow through the Fontan circulation still exhibits oscillatory waves as a result of pressure changes generated by the systemic single ventricle. Identification of discrete flow patterns through the Fontan circuit may be important to understand single ventricle performance. Ninety-seven patients with Fontan circulation underwent phase-contrast MRI of the right pulmonary artery, yielding subject-specific flow waveforms. Principal component (PC) analysis was performed on preprocessed flow waveforms. Principal components were then correlated with standard MRI indices of function, volume, and aortopulmonary collateral flow. The first principal component (PC) described systolic versus diastolic-dominant flow through the Fontan circulation, accounting for 31.3% of the variance in all waveforms. The first PC correlated with end-diastolic volume (R = 0.34, P = 0.001), and end-systolic volume (R = 0.30, P = 0.003), cardiac index (R = 0.51, P < 0.001), and the amount of aortopulmonary collateral flow (R = 0.25, P = 0.027)-lower ventricular volumes and a smaller volume of collateral flow-were associated with diastolic-dominant cavopulmonary flow. The second PC accounted for 19.5% of variance and described late diastolic acceleration versus deceleration and correlated with ejection fraction-diastolic deceleration was associated with higher ejection fraction. Principal components describing the diastolic flow variations in pulmonary arteries are related to the single ventricle function and volumes. Particularly, diastolic-dominant flow without late acceleration appears to be related to preserved ventricular volume and function, respectively.NEW & NOTEWORTHY The exact physiological significance of flow oscillations of phasic and temporal flow variations in Fontan circulation is unknown. With the use of principal component analysis, we discovered that flow variations in the right pulmonary artery of Fontan patients are related to the single ventricle function and volumes. Particularly, diastolic-dominant flow without late acceleration appears to be related to more ideal ventricular volume and systolic function, respectively.

Impact of aortopulmonary collateral flow and single ventricle morphology on longitudinal hemodynamics in Fontan patients: A serial CMR study

BackgroundSingle ventricle (SV) patients with a Fontan circulation are at risk for functional deterioration. The aim of this study was to assess longitudinal Fontan hemodynamics using serial cardiovascular magnetic resonance (CMR) data and to study the impact of aortopulmonary collateral (APC) flow and type of SV morphology. MethodsForty-one Fontan patients (age at first CMR 13.4 ± 6.0 years) with two CMR examinations within a time interval of at least 4 years (follow-up 5.3 ± 0.9 years) were included. The protocol consisted of short-axis cine volumetry and 2-dimensional blood flow measurements in the inferior vena cava (IVC), superior vena cava (SVC) and ascending aorta (Ao). APC flow was calculated as Ao – (SVC + IVC). Myocardial strain/strain rate was assessed using feature tracking technique. ResultsSV end-diastolic volume (p = 0.14) and ejection fraction (p = 0.70) remained constant. No significant changes in CMR derived myocardial strain/strain rate values were observed. Ao flow decreased (p = 0.01), IVC flow remained unchanged (p = 0.52), while SVC flow (p = 0.003) and APC flow (p = 0.006) decreased significantly. Patients with a systemic right ventricle (RV) showed unchanged APC flow and a further increase in SV size over time compared to patients with a systemic left ventricle. ConclusionsLongitudinal CMR data in a cohort of clinically stable Fontan patients revealed no significant changes in SV dimensions and myocardial performance while APC flow decreased spontaneously. Patients with a systemic RV seem to be at risk for permanent SV volume overload through APCs and might therefore benefit from consequent interventional APC embolization.

Aortopulmonary collateral flow quantification by MR at rest and during continuous submaximal exercise in patients with total cavopulmonary connection.

Aortopulmonary collateral flow is considered to have significant impact on the outcome of patients with single ventricle circulation and total cavopulmonary connection (TCPC). There is little information on collateral flow during exercise. To quantify aortopulmonary collateral flow at rest and during continuous submaximal exercise in clinical patients doing well with TCPC. Prospective, case controlled. Thirteen patients with TCPC (17 (11-37) years) and 13 age and sex-matched healthy controls (18 (11-38) years). 1.5T; free breathing; phase sensitive gradient echo sequence. Blood flow in the ascending and descending aorta and superior vena cava were measured at rest and during continuous submaximal physical exercise in patients and controls. Systemic blood flow (Qs ) was assumed to be represented by the sum of flow in the superior caval vein (Qsvc ) and the descending aorta (QAoD ) at the diaphragm level. Aortopulmonary collateral flow (Qcoll ) was calculated by subtracting Qs from flow in the ascending aorta (QAoA ). Mann-Whitney U-test and Wilcoxon test for comparison between groups and between rest and exercise. Absolute collateral flow in TCPC patients at rest was 0.4 l/min/m2 (-0.1-1.2), corresponding to 14% (-2-42) of Qs . Collateral flow did not change during exercise (difference -0.01 (-0.7-1.0) l/min/m2 , P = 0.97). TCPC patients had significantly lower Qs at rest (2.5 (1.6-4.1) vs. 3.5 (2.6-4.8) l/min/m2 , P = 0.001) and during submaximal exercise (3.2 (2.0-6.0) vs. 4.8 (3.3-6.9) l/min/m2 , P = 0.001), compared to healthy controls. The increase in Qs with exercise was also significantly lower in patients than in healthy controls (median 0.6 vs. 1.2 l/min/m2 , P < 0.02). Clinical patients doing well with TCPC have significant aortopulmonary collateral flow at rest (14% of Qs ) compared to healthy controls, which does not change during submaximal exercise. 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1509-1516.

Validation of a Mathematical Model of Bidirectional Glenn Circulation With Aortopulmonary Collaterals and the Implications for QP/QS Calculation

A mathematical model of the oxygen delivery kinetics of the bidirectional Glenn (BDG) shunt circulation incorporating aortopulmonary collateral (APC) flow was created. The model was used to characterize oxygen delivery and compare modeled data to actual patient data obtained using cardiac magnetic resonance imaging (MRI) and catheterization. In addition, cardiac MRI and catheterization assessment of pulmonary blood flow in the presence of APC flow were compared. Mathematical model and retrospective data analysis of patients who underwent cardiac MRI and catheterization. The mathematical model is based on the concept that APC flow to the lungs is recirculated pulmonary venous blood flow, which does not contribute to systemic oxygen delivery. Single-center, university teaching hospital. The study included 98 patients with BDG shunt undergoing cardiac MRI and cardiac catheterization. In the absence of APC flow, the pulmonary blood flow to systemic blood flow ratio (Qp/Qs) calculated using cardiac catheterization data closely matched that obtained with cardiac MRI. In the presence of APC flow, Qp/Qs calculated using cardiac catheterization data systematically underestimated values obtained with cardiac MRI. A mathematical model of BDG shunt oxygen delivery incorporating variable APC flow was created. The model provided reasonable prediction of actual patient data for arterial blood oxygen, superior vena cava oxygen saturation, and oxygen delivery obtained at the time of cardiac catheterization in patients. The oxygen delivery kinetics of a BDG shunt incorporating variable APC flow can be modeled mathematically. Model output can be used to predict blood oxygen saturation after coil embolization of APC flow in the cardiac catheterization laboratory.

Simulation of aortopulmonary collateral flow in Fontan patients for use in prediction of interventional outcomes.

Patients with complex congenital heart disease may need to be converted to a Fontan circulation with systemic venous return surgically connected to the pulmonary circulation. These patients frequently form aortopulmonary collaterals (APC), that is arterial inflows to the pulmonary artery vascular tree. The aim of this study was to develop a method to calculate the effect of APC on the pulmonary flow distribution based on magnetic resonance imaging (MRI) measurements and computational fluid dynamics simulations in order to enable prediction of interventional outcomes in Fontan patients. Patient-specific models of 11 patients were constructed in a 3D-design software based on MRI segmentations. APC flow was quantified as the difference between pulmonary venous flow and pulmonary artery flow, measured by MRI. A method was developed to include the modulating effect of the APC flow by calculating the patient-specific relative pulmonary vascular resistance. Simulations, including interventions with a Y-graft replacement and a stent dilatation, were validated against MRI results. The bias between simulated and MRI-measured fraction of blood to the left lung was 2·9±5·3%. Including the effects of the APC flow in the simulation (n=6) reduced simulation error from 9·8±7·0% to 5·2±6·3%. Preliminary findings in two patients show that the effect of surgical and catheter interventions could be predicted using the demonstrated methods. The work demonstrates a novel method to include APC flow in predictive simulations of Fontan hemodynamics. APC flow was found to have a significant contribution to the pulmonary flow distribution in Fontan patients.

Magnetic resonance imaging catheter stress haemodynamics post-Fontan in hypoplastic left heart syndrome.

Exercise limitation is common post-Fontan. Hybrid X-ray and magnetic resonance imaging (XMR) catheterization allows haemodynamic assessment by means of measurement of ventricular volumes and flow in major vessels with simultaneous invasive pressures. We aim to assess haemodynamic response to stress in patients with hypoplastic left heart syndrome (HLHS) post-Fontan. Prospective study of 13 symptomatic children (NHYA 2) with HLHS post-Fontan using XMR catheterization. Three conditions were applied: baseline (Stage 1), dobutamine at 10 µg/kg/min (Stage 2), and dobutamine at 20 µg/kg/min (Stage 3). Seven consecutive patients received inhaled nitric oxide (iNO) at peak stress. Control MRI data were from normal healthy adults. In the HLHS patients, baseline mean pulmonary vascular resistance (PVR) was 1.51 ± 0.59 WU m(2) and aortopulmonary collateral flow was 17.7 ± 13.6% of systemic cardiac output. Mean right ventricular end-diastolic pressure was 6.7 ± 2.5 mmHg which did not rise with stress. Cardiac index (CI) increased at Stage 2 in HLHS (40%) and controls (61%) but continued to increase at Stage 3 only in controls (19%) but not in HLHS. The blunted rise in CI in HLHS was due to a continuing fall in end-diastolic volume throughout stress, with no significant change in PVR or CI at peak stress in response to iNO. Cardiac output post-Fontan in HLHS at peak stress is blunted due to a limitation in preload which is not responsive to inhaled pulmonary vasodilators in the setting of normal PVR.

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

In the absence of an accessible chronic animal model of the Fontan circulation, computational modeling can provide insights into this unique circulatory arrangement, especially how differently it behaves from the normal mammalian circulation. Many groups have focused on refining a single element of the entire Fontan circulation-the total cavopulmonary connection (TCPC). Yet, only modest improvements in transplant-free survival have resulted. From an engineering perspective, optimizing the performance of a complex, multiparameter system requires an understanding of how the performance is affected by the full set of system parameters. We evaluated the hemodynamic impact of nine physiological perturbations in the two-year-old (yo) patient with hypoplastic left heart syndrome having a Fontan rearrangement (using our previously described lumped-parameter multicompartment model of both pulmonary and systemic circulations). In cases where comparison is appropriate, we evaluated the hemodynamic impact of analogous pathophysiologies in the normal two-year-olds. We operated the model in open-loop mode in order to expose the magnitude of the impact of uncompensated physiological perturbations. Without the benefit of compensatory mechanisms, a valvar regurgitant fraction of 50% is sufficient to drop the cardiac index (CI) to 2.0 L/min/m(2) or less. Aortopulmonary collateral flow of 0.6 L/min (1.1 L/min/m(2)) or 0.5 L/min (0.9 L/min/m(2)), sufficient to raise the ratio of pulmonary flow to systemic flow (Qp/Qs) to no higher than 1.2 or 1.5 (fenestration present or absent, respectively), is the maximum which could be tolerated (CI = 2.0 L/min/m(2)) without the help of compensatory mechanisms. Ventricular end-diastolic elastance (stiffness) changes have dramatic effects on CI in a Fontan circulatory arrangement. Several components of the Fontan circulation other than the TCPC actually have equal, or greater, impact on CI under certain conditions.

MRI shows limited mixing between systemic and pulmonary circulations in foetal transposition of the great arteries: a potential cause of in utero pulmonary vascular disease.

To investigate the relationship between foetal haemodynamics and postnatal clinical presentation in patients with transposition of the great arteries using phase-contrast cardiovascular magnetic resonance. A severe and irreversible form of persistent pulmonary hypertension of the newborn occurs in up to 5% of patients with transposition and remains an important cause of morbidity and mortality in these infants. Restriction at the foramen ovale and ductus arteriosus has been identified as a risk factor for the development of pulmonary hypertension, and this can now be studied with magnetic resonance imaging using a new technique called metric optimised gating. Blood flow was measured in the major vessels of four foetuses with transposition with intact ventricular septum (gestational age range: 35-38 weeks) and compared with values from 12 normal foetuses (median gestational age: 37 weeks; range: 34-40 weeks). We found significantly reduced flows in the ductus arteriosus (p<0.01) and foramen ovale (p=0.03) and increased combined ventricular output (p=0.01), ascending aortic (p=0.001), descending aortic (p=0.03), umbilical vein (p=0.03), and aorto-pulmonary collateral (p<0.001) flows in foetuses with transposition compared with normals. The foetus with the lowest foramen ovale shunt and highest aorto-pulmonary collateral flow developed fatal pulmonary vascular disease. We found limited mixing between the systemic and pulmonary circulations in a small group of late-gestation foetuses with transposition. We propose that the resulting hypoxia of the pulmonary circulation could be the driver behind increased aorto-pulmonary collateral flow and contribute to the development of pulmonary vascular disease in some foetuses with transposition.

Aortopulmonary Collateral Flow Is Related to Pulmonary Artery Size and Affects Ventricular Dimensions in Patients after the Fontan Procedure

BackgroundAortopulmonary 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.Methods60 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/m2 and group 2 > 0.495 l/min/m2.ResultsGroup 1 patients had significant smaller SV enddiastolic (71 ± 16 vs 87 ± 25 ml/m2; p=0.004) and endsystolic volumes (29 ± 11 vs 40 ± 21 ml/m2; 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).ConclusionsVolume 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.

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. The aim of this study was to detect and quantify APC flow using CMR and assess its impact on SV volume and function and to evaluate whether the size of the pulmonary arteries is related to the degree of APC flow.