Characterization of the Ejector Pump Performance for the Assisted Bidirectional Glenn Procedure

This study introduces an algebraic model informed by computational fluid dynamics (CFD) simulations to investigate the performance of the assisted bidirectional Glenn (ABG) operation on a broad range of conditions. The performance of this operation, as measured by the superior vena cava (SVC) pressure, depends on the nozzle area in its ejector pump and the patient’s pulmonary vascular resistance (PVR). Using the developed algebraic model to explore this two-dimensional parameter space shows that the ejector pump can create a pressure difference between the pulmonary artery and the SVC as high as 5 mmHg. The lowest SVC pressure is produced at a nozzle area that decreases linearly with the PVR such that, at PVR =4.2 (Wood units-m2), there is no added benefit in utilizing the ejector pump effect (optimal nozzle area is zero, corresponding to the bidirectional Glenn circulation). At PVR =2 (Wood units-m2), the SVC pressure can be lowered to less than 4 mmHg by using an optimal nozzle area of ≈2.5 mm2. Regardless of the PVR, adding a 2 mm2 nozzle to the baseline bidirectional Glenn boosts the oxygen saturation and delivery by at least 15%. The SVC pressure for that 2 mm2 nozzle remains below 14 mmHg for all PVRs less than 7 Wood units-m2. The mechanical efficiency of the optimal designs consistently remains below 30%, indicating the potential for improvement in the future. A good agreement is observed between the algebraic model and high-fidelity CFD simulations.

The Failed Bidirectional Glenn Shunt: Risk Factors for Poor Outcomes and the Role of Early Reoperation

Background: Bidirectional Glenn shunt (BDG) failure carries high morbidity and mortality but the clinical factors associated with failure and the optimal management strategy are understudied. Methods: A total of 217 patients undergoing BDG at our institution between 1989 and 2020 were retrospectively reviewed and categorized as success or failure. Failure was defined as the need for reoperation (BDG takedown, reoperation for correction of cardiac defect, and/or transplantation) at any time postoperatively; operative mortality (death attributable to BDG malfunction occurring during the index hospitalization for BDG or within 30 days of discharge); or late mortality (death directly attributable to BDG malfunction occurring prior to Fontan or next-stage palliation). Univariate and binary logistic regression analyses were performed. Results: BDG failure occurred in 14 (6.5%) patients. Univariate predictors were: hypoplastic left heart syndrome ( P = .037), right ventricular (RV) dominance ( P = .010), greater pre-BDG pulmonary vascular resistance (PVR) ( P = .012), concomitant atrioventricular valve repair ( P = .020), prolonged pleural drainage ( P = .001), intensive care unit ( P<.001) and hospital ( P = .002) stays, and extracorporeal membrane oxygenation (ECMO) requirement ( P<.001). Multivariate predictors were: RV dominance ( P = .002), greater PVR ( P = .041), ICU ( P<.001) and hospital ( P = .020) stays, and need for ECMO ( P<.001). As many as 10 of 14 (71%) patients with BDG failure died. Reoperation was performed for 10 patients with BDG failure. Five reoperation patients survived until discharge, with four patients alive at last follow-up (mean 7.9 years). Survivors underwent reoperation earlier than nonsurvivors (36 vs. 94 days). Conclusions: BDG failure carries high mortality, but preoperative predictors and postoperative indicators of failure exist. Early BDG takedown and insertion of aorta-pulmonary shunt may allow survival.

The Anaesthetic Management of a Parturient with an Ebstein Anomaly and Prior Bidirectional Glenn Shunt

Parturients with Ebstein anomaly are an anaesthetic challenge due to the spectrum of disease. Patients palliated with bidirectional Glenn shunts are susceptible to right heart dysfunction due to the physiological changes during parturition. We present a 28-year-old primigravida with Ebstein anomaly surgically managed by a bidirectional Glenn shunt. Echocardiograms showed normal right ventricular function despite reported dyspnea as the pregnancy progressed. Following a comprehensive plan developed during multidisciplinary prenatal meetings, she safely delivered. In this case report, we discuss the preoperative evaluation, management of labour and delivery, and postpartum planning of parturients with palliated Ebstein anomaly.

CFD Modeling of Blood Flow in a Bidirectional Glenn Shunt and a Combined Bidirectional Glenn and Blalock-Taussig Shunt

Cyanosis or “Blue Baby Syndrome,” is an infant disorder which affects the newly born babies whose skins turn blue or purple because of lack of required blood flow between heart and lung due to pulmonary vascular blockage. Many patients may also have stenosis in vessels. If there is not enough blood flow from heart to the lung, lack of oxygen will cause platelet aggregation and coagulation resulting in elevated wall shear stress which may potentially result in death. In order to address the congenital defect and increase blood flow and oxygen saturation levels within the blood pumping system, a biological shunt is usually planted between innominate veins and left and right pulmonary arteries. The well-known examples are Blalock-Taussig shunt (BT shunt) between right ventricle and pulmonary artery and bidirectional Glenn shunt (BGS) between innominate veins and pulmonary arteries. The goal of this paper is to study the hemodynamics of BGS, wherein the blood flow goes through superior vena cava (SVC), innominate and subclavian veins and pulmonary arteries. In another simulation, Blalok-Taussing shunt (BTS) is also included along with the BGS. In BTS, the blood directly flows between innominate and pulmonary artery. The models are created with SolidWorks and Blender software based on real patient aorta model parameters. The commercial CFD software ANSYS is used to simulate the blood flow. CFD simulations are performed for blood flow (1) in patient specific aorta model without BGS and (2) in patient specific model with both BGS and BTS. The results for distribution of pressure, velocity and wall shear stress are obtained and analyzed to evaluate the performance of BGS alone and with both BGS and BTS. The computations are compared with limited available clinical data. This study demonstrates how CFD can be effectively utilized in the design of medical devices such as BGS and BTS and to improve the clinical outcomes in patients.