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

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.

This study tested whether surgically modifiable shunt geometry might form a second, patient-specific approach to maintaining shunt patency, via management of thrombogenic hemodynamics.

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.

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 (ρ = 0.94, p < 0.001; ρ = 0.88, p = 0.002) and ESR (ρ = 0.82, p = 0.007; ρ = 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.

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.

What is new?: In patient-specific computational models of the modified Blalock-Taussig-Thomas shunt, thrombogenic blood flow patterns localize to the shunt-subclavian junction across anatomically diverse infants, identifying this as the key region of biomechanical vulnerability for deadly thrombus initiation.Surgically modifiable parameters, including insertion angle and shunt diameter, were identified as key determinants of local shear stress exposure.Thrombosed shunts exhibit higher cycle-averaged shear exposure than patent shunts, suggesting that cumulative hemodynamic burden may discriminate thrombosis risk.What are the clinical implications?: Infants with mBTTS are among the most heavily anticoagulated patients in pediatric cardiology, but anticoagulants do not meaningfully improve outcomes. This study shows that this is because systemic anticoagulation cannot modify the local mechanical environment that initiates clot formation at the shunt interface.Preoperative patient-specific computational modeling may help optimize shunt configuration to reduce thrombogenic risk.Geometry-informed surgical planning could complement pharmacologic strategies and advance personalized care in congenital heart palliation.