Surgically Modifiable Insertion Geometry Drives Thrombogenic Flow in the Modified Blalock-Taussig-Thomas Shunt

ABSTRACT Background: The modified Blalock-Taussig-Thomas shunt (mBTTS) sustains pulmonary blood flow in infants with cyanotic or single-ventricle heart disease, but shunt thrombosis occurs in 8-12% of cases and carries substantial mortality. Systemic anticoagulation has limited efficacy. Objectives: This study tested whether surgically modifiable shunt geometry might form a second, patient-specific approach to maintaining shunt patency, via management of thrombogenic hemodynamics. Methods: Three-dimensional mBTTS anatomies were reconstructed from computed tomography in 10 infants (4 thrombosed, 6 patent). Pulsatile inlet waveforms derived from Doppler ultrasound were coupled with three-element Windkessel outlet models individually calibrated to catheter-derived pressures. Transient computational fluid dynamics simulations predicted wall shear rate (WSR) and elongational strain rate (ESR). Associations between surgically relevant geometric parameters and hemodynamic metrics were evaluated. Results: Simulated pressures closely matched clinical measurements at all four outlets in all 10 models. Despite substantial anatomic variability, peak WSR and ESR consistently localized to the shunt-subclavian junction in 8 of 10 patients, including all 4 thrombosed shunts. Greater deviation of shunt insertion angle from perpendicular was associated with higher systolic and cycle-averaged normalized WSR ({rho} = 0.94, p < 0.001; {rho} = 0.88, p = 0.002) and ESR ({rho} = 0.82, p = 0.007; {rho} = 0.70, p = 0.03). Larger shunt diameter was associated with lower WSR and ESR. Thrombosed shunts demonstrated higher shear-related metrics than patent shunts, particularly during systole. Conclusions: In patient-specific mBTTS anatomies, insertion angle and shunt diameter are determinants of local abnormal flow, concentrated at the shunt-subclavian junction. Patient-specific hemodynamic assessment may inform shunt construction and interstage risk stratification.