Alternative Method to Restrict Blood Flow in Pulmonary Arteries during Stage 1 of
the Hybrid Procedure for Hypoplastic Left Heart Syndrome
Maarten Galantowicz
Figure 1: This figure shows the completed internal hypoplastic pulmonary artery banding
device. It consists of self-expandable stent, balloon expandable stent, and a Gortex shunt
covering.
Figure 2: This figure shows the internal constriction of the device. The external diameter is
10mm and the internal diameter is 5mm. The constriction is due to the balloon-expandable
stent.
Summary
Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease. It is
characterized by the underdevelopment of the left heart such as the left ventricle, mitral
valve, and aorta. This rarity causes decreased cardiac output and once born, the neonate's
heart cannot support systemic circulation. Recently, a new hybrid procedure was developed
to fix HSLS, which involves the expertise of interventional cardiologists and cardiothoracic
surgeons. The procedure involves three intense stages, and this project focuses on the first
stage. In the first stage, pulmonary artery bands, which are made out of
polytetrafluoroethylene (PTFE) tubing, are wrapped around both the left and right pulmonary
arteries to restrict blood flow to the lungs.
Although the bands work, they have significant issues. First, the surgery to insert the bands is
invasive and an increased risk to the patient. Also, the after being removed they leave
permanent scarring and an indentation, resulting an additional surgery to repair the
pulmonary artery (PA). Once, inserted the bands are fixed and do not adjust, which creates an
increasing problem as the child continues to grow over a six month period. After six months
the bands are usually too “tight” causing unwanted restriction and imbalanced circulation.
Finally, the procedure of inserting the bands hard to teach and surgeons have found it is even
sometimes not reproducible. This is due to the fact that the vasculature and the circulation in
every patient are different and therefore the amount of restriction will differ. In other words,
surgeons have to guess band tightness.
For this design project there are essentially two customers; the patient and the surgeon. The
patient values a device that involves the most non-invasive and comfortable procedure to set
the device. Also, the patient wants a device that functions properly such that it will minimize
side and long-term effects so that they can live a normal life after the hybrid procedure. The
surgeons’ requirements are that the device creates a fixed proximal resistance, balances
pulmonary, systemic, and coronary circulation, causes minimal injury to the patient,
adjustable, stability, reliability, and a device/procedure that is teachable and reproducible.
Six concepts were considered, all of which were internal devices and a
modification/manipulation of self-expandable or balloon expandable stents. Also, all of the
concepts involved utilizes the venturi effect to increase pulmonary resistivity. After
completing a design matrix to compare each concept based on the design requirements,
Concept #1 (1 (Self-Balloon Expandable Device with a PTFE covering) was chosen as the
final design. This concept was chosen because it was a simplest design that met all of the
design requirements, and could be fabricated from modified parts that were already on the
market.
The final design was fabricated from a self-expandable stent, a modified balloon expandable
stent, and a modified PTFE Gortex shunt. The Gortex shunt acted as the covering. A
successful prototype was fabricated, however, experimental testing in vivo was not
completed due to a lack of time and development, and currently there is not a PTFE covered
self-expandable stent. On the other hand, fluid flow calculations and fluid flow simulation
results show that the design can meet the required restriction of the pulmonary artery and
blood flow velocities without inducing turbulence. Further development of the device and the
fluid flow model will continue in the spring semester.