Complicated pediatric cardiac surgeries, such as staged Fontan reconstruction in children born with an univentricular heart, present great challenges when planning for each procedure. Unique anatomies bring unknowns into the physiologic (hemodynamics) equation, often requiring surgeons to make difficult decisions when predicting the outcome of a specific approach. Now scientists at Georgia Tech and clinicians at Children’s Hospital of Philadelphia have developed a software tool that analyzes patients’ own MRI scans to simulate various possible surgical options and their outcomes.
Georgia Tech reports:
The patient described in this paper, Amanda Mayer, age four, of Staten Island, N.Y., had previously undergone all three stages of the Fontan procedure at The Children’s Hospital of Philadelphia, but developed severe complications. Her oxygen saturation was very low—only 72 percent, compared to normal levels of at least 95 percent—which indicated the possibility of abnormal connections between the veins and arteries in one of her lungs. Normally, the liver releases hormonal factors that prevent these abnormal connections, so the presence of the malformations indicated a low supply of hepatic blood to the lung.
The image-based surgical planning consisted of five major steps: acquiring magnetic resonance images of the child’s heart at different times in the cardiac cycle, modeling the preoperative heart anatomy and blood flow, performing virtual surgeries, using computational fluid dynamics to model the proposed postoperative flow, and measuring the distribution of liver-derived hormonal factors and other clinically relevant parameters as feedback to the surgeon.
For this particular patient, the team saw a highly uneven flow distribution—the left lung was receiving about 70 percent of the blood pumped out by the heart, but only five percent of the hepatic blood. Both observations suggested left lung malformations, but closer examination of the flow structures in that particular patient revealed that the competition between different vessels at the center of the original Fontan connection effectively forced all hepatic factors into the right lung even though a vast majority of total cardiac output went to the left lung.
To facilitate the design of the surgical options that would correct this problem, Jarek Rossignac, Ph.D., a professor in Georgia Tech’s School of Interactive Computing, developed Surgem, an interactive geometric modeling environment that allowed the surgeon to use both hands and natural gestures in three-dimensions to grab, pull, twist and bend a three-dimensional computer representation of the patient’s anatomy. After analyzing the three-dimensional reconstruction of the failing cardiovascular geometry, the team considered three surgical options.
The research team then performed computational fluid dynamics simulations on all three options to investigate for each how well blood would flow to the lungs and the amount of energy required to drive blood through each connection design. These measures of clinical performance allowed the cardiologists and surgeons to conduct a risk/benefit analysis, which also included factors such as difficulty of completion and potential complications.
Of the three choices, Spray favored the option that showed a slightly higher energy cost but exhibited the best performance with regards to hepatic factor distribution to the left and right lungs. Five months after the surgery, Mayer showed a dramatic improvement in her overall clinical condition and oxygen saturation levels, which increased from 72 to 94 percent. Mayer is breathing easier and is now able to play actively like other children, according to her cardiologist, Donald Putman, M.D., of Staten Island, N.Y.
Here’s a short demo of the interactive surgical planner:
Image: (Top) 3D model of hepatic flow distribution pre-surgery. (Bottom) Post-surgery hepatic flow distribution options. The surgeon ultimately selected the third option. (Image courtesy of Ajit Yoganathan)
Full story: MRI Simulation of Blood Flow Helps Plan Child’s Delicate Heart Surgery…
Abstract in JACC Cardiovascular Imaging: Correction of Pulmonary Arteriovenous Malformation Using Image-Based Surgical Planning
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