Consequences of an early catheter-based intervention on pulmonary artery growth and right ventricular myocardial function in a pig model of pulmonary artery stenosis

30 Years' Experience in Percutaneous Pulmonary Artery Interventions in Transposition of the Great Arteries

Background

Pulmonary artery (PA) stenosis is common after arterial switch operation (ASO) for transposition of the great arteries (TGA). Differences between balloon angioplasty (BA) and stents on right ventricular (RV) and PA pressures are not well studied.

Objectives

The purpose of this study was to analyze percutaneous PA interventions' frequency after ASO, complications, and the effects of BA and stents on RV and PA pressures.

Methods

All TGA patients with ASO between 1977 and 2022 in 2 Dutch congenital heart centers were included in this multicenter retrospective study. Peri-operative ASO characteristics and pre-intervention and post-intervention invasive and echocardiographic data were analyzed.

Results

ASO was performed in 960 TGA patients, of which 888 survived 30 days and had complete follow-up. Seventy-seven (9%) underwent percutaneous PA interventions. Taussig-Bing anomaly (OR: 2.8; 95% CI: 1.228-6.168; P = 0.014), ASO time era 1990 to 1999 (OR: 4.7; 95% CI: 1.762-12.780; P = 0.002), and 2000 to 2009 (OR: 4.3; 95% CI: 1.618-11.330; P = 0.003) were independently associated with percutaneous PA interventions after ASO. Invasive post-interventional pressures and gradients were lower after stent implantation compared to BA (RV pressure: 47 ± 14 vs 58 ± 11; right PA-PA gradient: 11 ± 11 vs 25 ± 12, P < 0.05; RV/left ventricle pressure ratio: 0.4 ± 0.1 vs 0.6 ± 0.2, P < 0.001). Of the patients with unilateral PA stenosis (left PA: 41%, right PA: 59%), 77% showed increased RV pressure (>30 mm Hg) and RV/left ventricle pressure ratio improved post-intervention (0.5 ± 0.2 vs 0.6 ± 0.2, P < 0.05). Seventeen complications, most minor, were reported (13%). Two post-procedural deaths were reported.

Conclusions

Percutaneous PA interventions are common after ASO and can be performed safely but caution for serious complications is warranted. Unilateral PA stenosis can impact RV pressures. Stents may be more successful at treating PA stenosis compared to BA.

Estimating pulmonary arterial remodeling via an animal-specific computational model of pulmonary artery stenosis

Pulmonary artery stenosis (PAS) often presents in children with congenital heart disease, altering blood flow and pressure during critical periods of growth and development. Variability in stenosis onset, duration, and severity result in variable growth and remodeling of the pulmonary vasculature. Computational fluid dynamics (CFD) models enable investigation into the hemodynamic impact and altered mechanics associated with PAS. In this study, a one-dimensional (1D) fluid dynamics model was used to simulate hemodynamics throughout the pulmonary arteries of individual animals. The geometry of the large pulmonary arteries was prescribed by animal-specific imaging, whereas the distal vasculature was simulated by a three-element Windkessel model at each terminal vessel outlet. Remodeling of the pulmonary vasculature, which cannot be measured in vivo, was estimated via model-fitted parameters. The large artery stiffness was significantly higher on the left side of the vasculature in the left pulmonary artery (LPA) stenosis group, but neither side differed from the sham group. The sham group exhibited a balanced distribution of total distal vascular resistance, whereas the left side was generally larger in the LPA stenosis group, with no significant differences between groups. In contrast, the peripheral compliance on the right side of the LPA stenosis group was significantly greater than the corresponding side of the sham group. Further analysis indicated the underperfused distal vasculature likely moderately decreased in radius with little change in stiffness given the increase in thickness observed with histology. Ultimately, our model enables greater understanding of pulmonary arterial adaptation due to LPA stenosis and has potential for use as a tool to noninvasively estimate remodeling of the pulmonary vasculature.

The impact of unilateral pulmonary artery stenosis on right ventricular to pulmonary arterial coupling in patients with transposition of the great arteries

BACKGROUND

Unilateral pulmonary artery (PA) stenosis is common in the transposition of the great arteries (TGA) after arterial switch operation (ASO) but the effects on the right ventricle (RV) remain unclear.

AIMS

To assess the effects of unilateral PA stenosis on RV afterload and function in pediatric patients with TGA-ASO.

METHODS

In this retrospective study, eight TGA patients with unilateral PA stenosis underwent heart catheterization and cardiac magnetic resonance (CMR) imaging. RV pressures, RV afterload (arterial elastance [Ea]), PA compliance, RV contractility (end-systolic elastance [Ees]), RV-to-PA (RV-PA) coupling (Ees/Ea), and RV diastolic stiffness (end-diastolic elastance [Eed]) were analyzed and compared to normal values from the literature.

RESULTS

In all TGA patients (mean age 12 ± 3 years), RV afterload (Ea) and RV pressures were increased whereas PA compliance was reduced. RV contractility (Ees) was decreased resulting in RV-PA uncoupling. RV diastolic stiffness (Eed) was increased. CMR-derived RV volumes, mass, and ejection fraction were preserved.

CONCLUSION

Unilateral PA stenosis results in an increased RV afterload in TGA patients after ASO. RV remodeling and function remain within normal limits when analyzed by CMR but RV pressure-volume loop analysis shows impaired RV diastolic stiffness and RV contractility leading to RV-PA uncoupling.

Impact of Transcatheter Pulmonary Artery Intervention Following Superior Cavopulmonary Connection on Pulmonary Artery Growth

INTRODUCTION

Balloon and stent angioplasty of the pulmonary arteries (PAs) are frequently performed following superior cavopulmonary connection (SCPC), not only to normalize the caliber of the affected PA but also in hopes of maximizing downstream growth over time. There are limited data on the impact on subsequent PA growth prior to total cavopulmonary connection (TCPC).

METHODS

A single-center, retrospective cohort study was performed on children who underwent transcatheter (TC) PA intervention following SCPC between January 1, 2010, and December 31, 2018. Growth of treated and contralateral PAs was measured at the lobar bifurcation (distal branch PA [DBPA]) and in the proximal lower lobe (lower lobe branch [LLB]) on serial angiograms. Growth rate was evaluated using a mixed-effect model clustered by individual patient with an interaction term for treated PA and time to evaluate for differential growth rates between treated and contralateral PAs.

RESULTS

Thirty-five patients underwent TC PA intervention following SCPC, at a median of 70 days (interquartile range: 19-297 days) postoperatively. Significant growth was seen at both DBPA and LLB for raw (0.8 mm/year, 95% CI: 0.6-1.0, P < .001 for both) and body surface area (BSA) adjusted measures (8.4mm/m²/year, 95% CI: 5.6-11.2, P < .001; 7.9 mm/m²/year, 95% CI: 5.5-10.2, P < .001). The growth rate of the treated vessel was not significantly different from that of the contralateral vessel at the DBPA or LLB positions for raw (P = .71, .70) or BSA-adjusted measurements (P = .86, .64).

CONCLUSION

Transcatheter PA intervention was associated with normal distal PA growth rate relative to the untreated side.

Non-invasive MRI Derived Hemodynamic Simulation to Predict Successful vs. Unsuccessful Catheter Interventions for Branch Pulmonary Artery Stenosis: Proof-of-Concept and Experimental Validation in Swine

OBJECTIVE

This study assessed the ability of hemodynamic simulations to predict the success of catheter interventions in a swine model of branch pulmonary artery stenosis (bPAS).

BACKGROUND

bPAS commonly occurs in congenital heart disease and is often managed with catheter based interventions. However, despite technical success, bPAS interventions do not lead to improved distal pulmonary blood flow (PBF) distribution in approximately 1/3rd of patients. New tools are needed to better identify which patients with bPAS would most benefit from catheter interventions.

METHODS

For 13 catheter intervention cases in swine with surgically created left PAS (LPAS), PA pressures from right heart catheterization (RHC) and PBF distributions from MRI were measured before and after catheter interventions. Hemodynamic simulations with a reduced order computational fluid dynamics (CFD) model were performed using non-invasive PBF measurements derived from MRI, and then correlated with changes in invasive measures of hemodynamics and PBF distributions before and after catheter intervention to relieve bPAS.

RESULTS

Compared to experimentally measured changes in left PBF distribution, simulations had a small bias (3.4 ± 11.1%), moderate agreement (ICC = 0.69 [0.24-0.90], 0.71 [0.23-0.91]), and good diagnostic capability to predict successful interventions (> 20% PBF increase) (AUC 0.83 [0.59-1.0]). Simulations had poorer prediction of changes in stenotic pressure gradient (ICC = 0.28 [- 0.33 to 0.73], r = 0.57 [- 0.04 to 0.87]) and MPA systolic pressure (ICC = 0.00 [- 0.52 to 0.53], r = 0.29 [- 0.32 to 0.72]).

CONCLUSION

While there was only weak to moderate agreement between predicted and measured changes in PA pressures and pulmonary blood flow distributions, hemodynamic simulations did show good diagnostic value for predicting successful versus unsuccessful catheter based interventions to relieve bPAS. The results of this proof of concept study are promising and should encourage future development for using hemodynamic models in planning interventions for patients with bPAS.

Accelerated Estimation of Pulmonary Artery Stenosis Pressure Gradients with Distributed Lumped Parameter Modeling vs. 3D CFD with Instantaneous Adaptive Mesh Refinement: Experimental Validation in Swine

Branch pulmonary artery stenosis (PAS) commonly occurs in congenital heart disease and the pressure gradient over a stenotic PA lesion is an important marker for re-intervention. Image based computational fluid dynamics (CFD) has shown promise for non-invasively estimating pressure gradients but one limitation of CFD is long simulation times. The goal of this study was to compare accelerated predictions of PAS pressure gradients from 3D CFD with instantaneous adaptive mesh refinement (AMR) versus a recently developed 0D distributed lumped parameter CFD model. Predictions were then experimentally validated using a swine PAS model (n = 13). 3D CFD simulations with AMR improved efficiency by 5 times compared to fixed grid CFD simulations. 0D simulations further improved efficiency by 6 times compared to the 3D simulations with AMR. Both 0D and 3D simulations underestimated the pressure gradients measured by catheterization (- 1.87 ± 4.20 and - 1.78 ± 3.70 mmHg respectively). This was partially due to simulations neglecting the effects of a catheter in the stenosis. There was good agreement between 0D and 3D simulations (ICC 0.88 [0.66-0.96]) but only moderate agreement between simulations and experimental measurements (0D ICC 0.60 [0.11-0.86] and 3D ICC 0.66 [0.21-0.88]). Uncertainty assessment indicates that this was likely due to limited medical imaging resolution causing uncertainty in the segmented stenosis diameter in addition to uncertainty in the outlet resistances. This study showed that 0D lumped parameter models and 3D CFD with instantaneous AMR both improve the efficiency of hemodynamic modeling, but uncertainty from medical imaging resolution will limit the accuracy of pressure gradient estimations.

Stent interventions for pulmonary artery stenosis improve bi-ventricular flow efficiency in a swine model

BACKGROUND

Branch pulmonary artery (PA) stenosis (PAS) commonly occurs in patients with congenital heart disease (CHD). Prior studies have documented technical success and clinical outcomes of PA stent interventions for PAS but the impact of PA stent interventions on ventricular function is unknown. The objective of this study was to utilize 4D flow cardiovascular magnetic resonance (CMR) to better understand the impact of PAS and PA stenting on ventricular contraction and ventricular flow in a swine model of unilateral branch PA stenosis.

METHODS

18 swine (4 sham, 4 untreated left PAS, 10 PAS stent intervention) underwent right heart catheterization and CMR at 20 weeks age (55 kg). CMR included ventricular strain analysis and 4D flow CMR.

RESULTS

4D flow CMR measured inefficient right ventricular (RV) and left ventricular (LV) flow patterns in the PAS group (RV non-dimensional (n.d.) vorticity: sham 82 ± 47, PAS 120 ± 47; LV n.d. vorticity: sham 57 ± 5, PAS 78 ± 15 p < 0.01) despite the PAS group having normal heart rate, ejection fraction and end-diastolic volume. The intervention group demonstrated increased ejection fraction that resulted in more efficient ventricular flow compared to untreated PAS (RV n.d. vorticity: 59 ± 12 p < 0.01; LV n.d. vorticity: 41 ± 7 p < 0.001).

CONCLUSION

These results describe previously unknown consequences of PAS on ventricular function in an animal model of unilateral PA stenosis and show that PA stent interventions improve ventricular flow efficiency. This study also highlights the sensitivity of 4D flow CMR biomarkers to detect earlier ventricular dysfunction assisting in identification of patients who may benefit from PAS interventions.

Longitudinal Evolution of Pulmonary Artery Wall Shear Stress in a Swine Model of Pulmonary Artery Stenosis and Stent Interventions

Branch pulmonary artery stenosis (PAS) commonly occurs in congenital heart disease and it has previously been hypothesized that in branch PAS the pulmonary arteries (PAs) remodel their lumen diameter to maintain constant wall shear stress (WSS). We quantified the longitudinal progression of PA WSS in a swine model of unilateral PAS and two different intervention time courses to test this hypothesis. To quantify WSS in the entire pulmonary tree we used 4D Flow MRI for the large-proximal PAs and a structured tree model for the small-distal PAs. Our results only partially supported the hypothesis that in branch PAS the PAs remodel their lumen diameter to maintain WSS homeostasis. Proximal PA WSS was similar between groups at the final study time-point but WSS of mid-sized (5 mm to 500 μm) PA segments was found to be different between the sham and LPAS groups. This suggests that WSS homeostasis may only be achieved for the large-proximal PAs. Additionally, our results do not show WSS homeostasis being achieved over shorter periods of time suggesting that any potential WSS dependent changes in PA lumen diameter were a long-term remodeling response rather than a short-term vasodilation response. Future studies should confirm if these findings hold true in humans and investigate the impacts of WSS at different levels of the pulmonary tree on growth.

Pulmonary artery and lung parenchymal growth following early versus delayed stent interventions in a swine pulmonary artery stenosis model

OBJECTIVES

Compare lung parenchymal and pulmonary artery (PA) growth and hemodynamics following early and delayed PA stent interventions for treatment of unilateral branch PA stenosis (PAS) in swine.

BACKGROUND

How the pulmonary circulation remodels in response to different durations of hypoperfusion and how much growth and function can be recovered with catheter directed interventions at differing time periods of lung development is not understood.

METHODS

A total of 18 swine were assigned to four groups: Sham (n = 4), untreated left PAS (LPAS) (n = 4), early intervention (EI) (n = 5), and delayed intervention (DI) (n = 5). EI had left pulmonary artery (LPA) stenting at 5 weeks (6 kg) with redilation at 10 weeks. DI had stenting at 10 weeks. All underwent right heart catheterization, computed tomography, magnetic resonance imaging, and histology at 20 weeks (55 kg).

RESULTS

EI decreased the extent of histologic changes in the left lung as DI had marked alveolar septal and bronchovascular abnormalities (p = .05 and p < .05 vs. sham) that were less prevalent in EI. EI also increased left lung volumes and alveolar counts compared to DI. EI and DI equally restored LPA pulsatility, R heart pressures, and distal LPA growth. EI and DI improved, but did not normalize LPA stenosis diameter (LPA/DAo ratio: Sham 1.27 ± 0.11 mm/mm, DI 0.88 ± 0.10 mm/mm, EI 1.01 ± 0.09 mm/mm) and pulmonary blood flow distributions (LPA-flow%: Sham 52 ± 5%, LPAS 7 ± 2%, DI 44 ± 3%, EI 40 ± 2%).

CONCLUSION

In this surgically created PAS model, EI was associated with improved lung parenchymal development compared to DI. Longer durations of L lung hypoperfusion did not detrimentally affect PA growth and R heart hemodynamics. Functional and anatomical discrepancies persist despite successful stent interventions that warrant additional investigation.

Comparison of pulmonary artery dimensions in swine obtained from catheter angiography, multi-slice computed tomography, 3D-rotational angiography and phase-contrast magnetic resonance angiography

Accurate pulmonary artery (PA) imaging is necessary for management of patients with complex congenital heart disease (CHD). The ability of newer imaging modalities such as 3D rotational angiography (3DRA) or phase-contrast magnetic resonance angiography (PC-MRA) to measure PA diameters has not been compared to established angiography techniques. Measurements of PA diameters (including PA stenosis and PA stents) from 3DRA and non-contrast-enhanced PC-MRA were compared to 2D catheter angiography (CA) and multi-slice computed tomography (MSCT) in a swine CHD model (n = 18). For all PA segments 3DRA had excellent agreement with CA and MSCT (ICC = 0.94[0.91-0.95] and 0.92[0.89-0.94]). 3DRA PA stenosis measures were similar to CA and MSCT and 3DRA was on average within 5% of 10.8 ± 1.3 mm PA stent diameters from CA and MSCT. For compliant PA segments, 3DRA was on average 3-12% less than CA (p < 0.05) and MSCT (p < 0.01) for 6-14 mm vessels. PC-MRA could not reliably visualize stents and distal PA vessels and only identified 34% of all assigned measurement sites. For measured PA segments, PC-MRA had good agreement to CA and MSCT (ICC = 0.87[0.77-0.92] and 0.83[0.72-0.90]) but PC-MRA overestimated stenosis diameters and underestimated compliant PA diameters. Excellent CA-MSCT PA diameter agreement (ICC = 0.95[0.93-0.96]) confirmed previous data in CHD patients. There was little bias in PA measurements between 3DRA, CA and MSCT in stenotic and stented PAs but 3DRA underestimates measurements of compliant PA regions. Accurate PC-MRA imaging was limited to unstented proximal PA anatomy.

4D Flow MRI Estimation of Boundary Conditions for Patient Specific Cardiovascular Simulation

Accurate image based cardiovascular simulations require patient specific boundary conditions (BCs) for inlets, outlets and vessel wall mechanical properties. While inlet BCs are typically determined non-invasively, invasive pressure catheterization is often used to determine patient specific outlet BCs and vessel wall mechanical properties. A method using 4D Flow MRI to non-invasively determine both patient specific outlet BCs and vessel wall mechanical properties is presented and results for both in vitro validation with a latex tube and an in vivo pulmonary artery stenosis (PAS) stent intervention are presented. For in vitro validation, acceptable agreement is found between simulation using BCs from 4D Flow MRI and benchtop measurements. For the PAS virtual intervention, simulation correctly predicts flow distribution with 9% error compared to MRI. Using 4D Flow MRI to noninvasively determine patient specific BCs increases the ability to use image based simulations as pressure catheterization is not always performed.