Patient-Specific Multiscale Modeling of the Assisted Bidirectional Glenn

Abstract

Background: First-stage palliation of neonates with single-ventricle physiology is associated with poor outcomes and challenging clinical management. Prior computational modeling and in vitro experiments introduced the assisted bidirectional Glenn (ABG), which increased pulmonary flow and oxygenation over the bidirectional Glenn (BDG) and the systemic-to-pulmonary shunt in idealized models. In this study, we demonstrate that the ABG achieves similar performance in patient-specific models and assess the influence of varying shunt geometry.

Methods: In a small cohort of single-ventricle prestage 2 patients, we constructed three-dimensional in silico models and tuned lumped parameter networks to match clinical measurements. Each model was modified to produce virtual BDG and ABG surgeries. We simulated the hemodynamics of the stage 1 procedure, BDG, and ABG by using multiscale computational modeling, coupling a finite-element flow solver to the lumped parameter network. Two levels of pulmonary vascular resistances (PVRs) were investigated: baseline (low) PVR of the patients and doubled (high) PVR. The shunt nozzle diameter, anastomosis location, and shape were also manipulated.

Results: The ABG increased the pulmonary flow rate and pressure by 15% to 20%, which was accompanied by a rise in superior vena caval pressure (2 to 3 mm Hg) at both PVR values. Pulmonary flow rate and superior vena caval pressures were most sensitive to the shunt nozzle diameter.

Conclusions: Patient-specific ABG performance was similar to prior idealized simulations and experiments, with good performance at lower PVR values in the range of measured clinical data. Larger shunt outlet diameters and lower PVR led to improved ABG performance.

Fig 1.

Schematic of assisted bidirectional Glenn (ABG) shunt geometry, illustrating the shunt narrowing proximal to the superior vena cava (SVC). (D = main shunt diameter; d = luminal outlet diameter.)

Fig 2.

Flow rate through the largest pulmonary artery for each patient, comparing bidirectional Glenn (BDG) and assisted bidirectional Glenn (ABG). (RMS = root mean square.)

Fig 3.

Simulated flow speed in a plane bisecting the assisted bidirectional Glenn (ABG) shunt and the superior vena cava (SVC). Shunt flow is right to left. Shunts have nozzle diameters of (A) 0.6 mm, (B) 1.2 mm, and (C) 1.8 mm. (D) Pulmonary flow versus SVC pressure in the ABG, varying nozzle diameters. Arrows compare the same anatomic models at different pulmonary vascular resistance (PVR). (BDG = bidirectional Glenn.)

Fig 4.

Clinically relevant parameters of (A) shunt flow rate, (B) pulmonary flow rate, (C) pressure, and (D) heart load versus assisted bidirectional Glenn (ABG) nozzle diameters; the bidirectional Glenn (BDG) is shown as a zero-diameter variant of the ABG. *Modified Blalock-Taussig shunt values. (PVR = pulmonary vascular resistance; SVC = superior vena cava.)

Fig 5.

Simulated flow speed in a plane bisecting the assisted bidirectional Glenn (ABG) shunt and the superior vena cava (SVC) for (A) an elliptical nozzle and (B) an anastomosis near the SVC–pulmonary junction. (C) Flow rate through the largest pulmonary artery, comparing anastomosis location. (BDG = bidirectional Glenn; PI = pulsatility index.)