The assisted bidirectional Glenn: a novel surgical approach for first-stage single-ventricle heart palliation

Abstract

Background: Outcomes after a modified Blalock-Taussig shunt (mBTS) in neonates with single-ventricle physiology remain unsatisfactory. However, initial palliation with a superior cavopulmonary connection, such as a bidirectional Glenn (BDG), is discouraged, owing to potential for inadequate pulmonary blood flow (PBF). We tested the feasibility of a novel surgical approach, adopting the engineering concept of an ejector pump, whereby the flow in the BDG is "assisted" by injection of a high-energy flow stream from the systemic circulation.

Methods: Realistic 3-dimensional models of the neonatal mBTS and BDG circulations were created. The "assisted" bidirectional Glenn (ABG) consisted of a shunt between the right innominate artery and the superior vena cava (SVC), with a 1.5-mm clip near the SVC anastomosis to create a Venturi effect. The 3 models were coupled to a validated hydraulic circulation model, and 2 pulmonary vascular resistance (PVR) values (7 and 2.3 Wood units) were simulated.

Results: The ABG provided the highest systemic oxygen saturation and oxygen delivery at both PVR levels. In addition to achieving higher PBF than the BDG, the ABG produced a lower single-ventricular workload than mBTS. SVC pressure was highest in the ABG model (ABG: 15; Glenn: 11; mBTS: 3 mm Hg; PVR = 7 Wood units), but at low PVR, the SVC pressure was significantly lower (ABG: 8; Glenn: 6; mBTS: <3 mm Hg).

Conclusions: Adopting the principle of an ejector pump, with additional flow directed into the SVC in a BDG, the ABG appears to increase PBF with a modest increase in SVC and pulmonary arterial pressure. Although multiscale modeling results demonstrate the conceptual feasibility of the ABG circulation, further technical refinement and investigations are necessary, especially in an appropriate animal model.

FIGURE 1.

Idealized models of the mBTS, ABG, and BDG (top row). Colors in the circulation schematics (bottom row) represent the level of oxygen concentration. mBTS, Modified Blalock-Taussig shunt; ABG, assisted bidirectional Glenn; BDG, bidirectional Glenn; RCCA, right common carotid artery; BT, Blalock-Taussig shunt; BA, brachiocephalic artery; SVC, superior vena cava; PA, pulmonary arteries; DA, descending aorta; AA, ascending aorta; CA, coronary arteries; Q_ub, upper-body flow rate; UB, upper body; C_svc, superior vena cava oxygen concentration; C_ao, aortic oxygen concentration; Q_s, systemic flow rate; C_p, pulmonary vein oxygen concentration; PB, pulmonary bed; Q_p, pulmonary flow rate; Q_lb, lower-body flow rate; LB, lower body; C_ivc, inferior vena cava oxygen concentration.

FIGURE 2.

A schematic of an industrial ejector pump. This device transfers the energy of higher-pressure flow to lower-pressure flow, thus elevating the pressure at the outlet. Based on the same concept, flow through the SVC can be assisted by flow through the shunt to obtain a higher pressure at the PA without increasing SVC pressure. PA, Pulmonary artery; SVC, superior vena cava.

FIGURE 3.

Lumped parameter network coupled to the assisted bidirectional anatomy. This network contains blocks for the UBA, UBB, UBV, PAB, PVB, LBA, LBB, LBV, 2 CAs, the CB, CV, LA, RA, and SV. Two geometries, clipped and straight, are shown for the BA-SVC shunt. In the assisted bidirectional Glenn, pulmonary flow is supplied through the SVC and the shunt. UBB, Upper-body capillary bed; UBA, upper-body arteries; UBV, upper-body veins; BA-SVC, brachiocephalic-superior vena cava; AA, ascending aorta; SVC, superior vena cava; PAB, pulmonary artery bed; PVB, pulmonary vein bed; CV, coronary veins; CB, coronary capillary bed; CA, coronary artery; P_v, ventricular pressure; LA, left atrium; RA, right atrium; SV, single ventricle; LBV, lower-body veins; LBB, lower-body capillary bed; LBA, lower-body arteries.

FIGURE 4.

mBTS, BDG, and ABG heart load, oxygen delivery, pulmonary flow rate, systemic oxygen saturation, and SVC pressure at normal (white) and high (gray) PVR. SVC, Superior vena cava; mBTS, modified Blalock-Taussig shunt; N, normal; H, high; BDG, bidirectional Glenn; ABG, assisted bidirectional Glenn.