Heart surgeons now have a better grasp of the effects of different surgical approaches thanks to researchers at the Georgia Institute of Technology (Atlanta) collaborating with pediatric cardiologists and surgeons at The Children's Hospital of Philadelphia.
The team reported that they have developed a tool for virtual surgery that allows heart surgeons to view the predicted effects of different surgical approaches.
They found that by manipulating three-dimensional cardiac magnetic resonance images of a patient's specific anatomy, surgeons can view how alternative approaches affect blood flow and expected outcomes, and can select the best approach for each patient before entering the operating room.
"What we're doing is looking at the anatomy of a patient and we're creating a computer model of the heart," Ajit Yoganathan, PhD, Regents' Professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University (Atlanta) told Medical Device Daily. "This has been ongoing research for the last seven to eight years."
The researchers describe the surgical planning methodology, detailing how the tool helped them to plan the surgery of a four-year-old who was born with just one functional ventricle, or pumping chamber, instead of two, in the August issue of the Journal of the American College of Cardiology: Cardiovascular Imaging.
"We know that in this particular case the left lung was impacted," Yoganathan said. "So far this procedure has been done on three other children."
Two in every 1,000 babies in the U.S. are born with this type of single ventricle heart defect. These children typically suffer from low levels of oxygen in their tissues because their oxygen-rich and oxygen-poor bloods mix in their one functional ventricle before being redistributed to their lungs and body.
The children usually undergo a series of three open-heart surgeries - called the staged Fontan reconstruction - to reshape the circulation in a way that allows oxygen-poor blood to flow from the limbs directly to the lungs without going through the heart. While these vascular modifications can eliminate blood mixing and restore normal oxygenation levels, surgeons and cardiologists must ensure that the lungs will receive proper amounts of blood and nutrients after the surgery so that normal development occurs.
But the new imaging technique eliminates the need for these multiple surgeries and gives surgeons a chance to get to the heart of the matter.
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.
From the model researchers reconstructed the three-dimensional pre-operative flow fields to understand the underlying causes of the malformations.
For the 4-year-old patient, the team saw a highly uneven flow distribution - the left lung was receiving about 70% of the blood pumped out by the heart, but only 5% 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, researchers 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.
The research team came up with three options and 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.
"The final thought is that these kids go through multiple surgeries before they are able see any results," Yoganathan said. "With this method we're able to see what procedure works best first and eliminate the need for constant surgery."
Omar Ford, 404-262-5546; firstname.lastname@example.org