MRI Simulation of Blood Flow Helps Plan Child's Heart Surgery

/PRNewswire/ -- Researchers at the Georgia Institute of Technology, collaborating with pediatric cardiologists and surgeons at The Children's Hospital of Philadelphia, have developed a tool for virtual surgery that allows heart surgeons to view the predicted effects of different surgical approaches. By manipulating three-dimensional cardiac magnetic resonance images of a patient's specific anatomy, physicians can compare how alternative approaches affect blood flow and expected outcomes, and can select the best approach for each patient before entering the operating room.

"This tool helps us to get the best result for each patient," said co-author Mark A. Fogel, M.D., an associate professor of cardiology and radiology, and director of Cardiac MRI at The Children's Hospital of Philadelphia. "The team can assess the different surgical options to achieve the best blood flow and the optimum mixture of blood, so we can maximize the heart's energy efficiency."

In the August issue of the Journal of the American College of Cardiology: Cardiovascular Imaging, the researchers describe the surgical planning methodology, detailing how the tool helped them to plan the surgery of a four-year-old girl who was born with just one functional ventricle, or pumping chamber, instead of two.

Two in every 1,000 babies in the United States 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 blood mix in their one functional ventricle before being redistributed to their lungs and body.

To correct this, the children 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.

"Preoperatively determining the Fontan configuration that will achieve balanced blood flow to the lungs is very difficult and the wide variety and complexity of patients' anatomies requires an approach that is very specific and personalized," said Ajit Yoganathan, Ph.D., Regents' Professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. "With our surgical planning framework, the physicians gain a better understanding of each child's unique heart defect, thus improving the surgery outcome and recovery time."

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.

To improve the distribution of these hormonal factors to both lungs, the surgeons needed to re-operate and reconfigure the patient's cardiovascular anatomy. Georgia Tech's surgical planning framework helped Thomas L. Spray, M.D., chief of the Division of Cardiothoracic Surgery at Children's Hospital, to determine the optimal surgical option.

"MRI acquires images of the child's heart without using radiation," said Spray. "Then we use the computerized technology to model different connections to simulate optimum blood flow characteristics, before we perform the surgery."

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.

Fogel collected three different types of magnetic resonance images, and Yoganathan, along with graduate students Kartik Sundareswaran and Diane de Zelicourt, generated a three-dimensional model of the child's cardiovascular anatomy. From the model they reconstructed the three-dimensional pre-operative flow fields to understand the underlying causes of the malformations.

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.

"The ability to perform this work is a team effort," Fogel added. "State-of-the-art three-dimensional cardiac MRI married to modern biomedical engineering and applied anatomy and physiology enabled this approach. With the advanced pediatric cardiothoracic surgery we have here at The Children's Hospital of Philadelphia, patients can benefit from this new method."

Additional authors on the paper include Shiva Sharma from Pediatric Cardiology Services, Kirk Kanter from the Division of Cardiothoracic Surgery at Emory University, and Fotis Sotiropoulos from the Department of Civil Engineering at the University of Minnesota.

This work was funded by grant number HL67622 from the National Heart, Lung and Blood Institute (NHLBI) of the National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not necessarily represent the official view of the NHLBI or the NIH.

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Do You Know You're Having a Stroke?

/PRNewswire-USNewswire/ -- A Mayo Clinic study shows a majority of stroke patients don't think they're having a stroke -- and as a result -- delay seeking treatment until their condition worsens. The findings appear in the current issue of Emergency Medicine Journal at http://emj.bmj.com/.

Researchers studied 400 patients who were diagnosed at Mayo Clinic's emergency department with either acute ischemic stroke or a transient ischemic attack (TIA), a temporary interruption of blood flow to part of the brain.

Less than half of the patients -- 42 percent -- thought they were having a stroke. In fact, most in the study did not go to the emergency room when symptoms appeared. The median time from onset of symptoms to arrival at the hospital was over three and a half hours. Most said they thought the symptoms would simply go away. The delay in seeking medical help was the same among men and women.

When asked how they knew about stroke symptoms, nearly one-fifth said they thought a stroke always came on gradually. Just over half (51.9 percent) said they thought that seeking medical care immediately was important.

Significance of the findings

"Time is crucial in treating stroke," says Latha Stead, M.D., emergency medicine specialist and lead author of the study. "Each individual's medical background differs and affects recovery, but in general the sooner a patient experiencing a stroke reaches emergency care, the more likely the stroke can be limited and the condition managed to prevent further damage and improve recovery." The researchers say their findings clearly indicate that better public understanding of stroke symptoms will lead to a faster response and better outcomes.

What you should know

Strokes can happen quickly or can occur over several hours, with the condition continually worsening. The thrombus or clot that is causing the stroke can frequently be dissolved or disintegrated so blood can again flow to the brain. In such cases, immediate treatment can mean the difference between a slight injury and a major disability. Interestingly only 20.8 percent of the participants knew about such treatment. By use of stents, medications and other technology, physicians can stop a stroke from spreading and greatly limit damage. Stroke symptoms include:

* Sudden numbness, weakness, or paralysis of your face, arm or leg -- usually on one side of the body

* Sudden difficulty speaking or understanding speech (aphasia)
* Sudden blurred, double or decreased vision
* Sudden dizziness, loss of balance or loss of coordination

* A sudden, severe "bolt out of the blue" headache or an unusual headache, which may be accompanied by a stiff neck, facial pain, pain between your eyes, vomiting or altered consciousness

* Confusion or problems with memory, spatial orientation or perception

In such cases, a stroke gives no warning. But one possible sign of an impending stroke is a TIA. The signs and symptoms of TIA are the same as for a stroke, but they last for a shorter period -- several minutes to a few hours -- and then disappear, without leaving apparent permanent effects. You may have more than one TIA, and the signs and symptoms may be similar or different. A TIA indicates a serious risk that a full-blown stroke may follow.

Other Mayo researchers involved in the study were Lekshmi Vaidyanathan, M.B.B.S.; Maria Bellolio, M.D.; Rahul Kashyap, M.B.B.S.; Anjali Bhagra, M.B.B.S.; Rachel Gilmore, M.B.B.Ch.; Wyatt Decker, M.D.; Sailaja Enduri, M.B.B.S.; Shaily Mishra, Ph.D.; Helen Wood, R.N.; Ayman Yassa, M.D.; Ann Hoff, M.D.; and Robert Brown, M.D. Dr. Stead is supported by the Mayo Emergency Medicine Research Career Development Award and Mayo Clinic.

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GT Designs Prosthetic Vein Valve to Improve Venous Blood Flow

Engineers at the Georgia Institute of Technology have developed a prosthetic vein valve to help improve the lives of those suffering from a condition known as chronic venous insufficiency. The condition, which affects more than seven million people in the United States alone, occurs when valves in a person’s veins can no longer ensure a one-way flow of blood back to the heart.

“Blood flows to the toes because of gravity, but the body uses vein valves to pump blood in one direction back to the heart,” said David Ku, the Lawrence P. Huang Endowed Chair in Engineering and Entrepreneurship and Regents’ Professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. “However, sometimes a vein valve dissolves away after a blood clot. The loss of the valve leaflets allows blood to flow the wrong way, causing swelling in the legs and ankles.”

Ku is leading a research team that has developed a prosthetic vein valve to replace damaged, non-functioning valves. The prosthetic vein valve design and results from laboratory studies were presented at the Society for Biomaterials Fall Symposium in Atlanta on September 12. The research – under way for the past five years – is funded by the Wallace H. Coulter Foundation and the National Collegiate Inventors and Innovators Alliance.

Ku’s collaborators on this project include Rudy Gleason, an assistant professor with joint appointments in the Georgia Tech School of Mechanical Engineering and Department of Biomedical Engineering; Ross Milner, an assistant professor of surgery at Emory University; consultant Harris Bergman, a former Georgia Tech graduate student and now president of Amigent; former Georgia Tech graduate students Rahul Sathe and Laura-Lee Farrell; and current graduate students David Bark and Prem Midha.

Individuals with chronic venous insufficiency are commonly prescribed therapies – including anticoagulants, bed rest and compression hosiery – that target their symptoms rather than the cause. Damaged vein valves can sometimes be repaired, but when that isn’t possible, some surgical options are available to replace deep venous valves, such as valve transplantation. However, replacing the valve with a prosthetic one is likely the better option because finding a suitable donor valve in one of the patient’s legs can be difficult, according to Ku.

“Previous studies have shown that even if a donor valve is found, implanting it can cause significant trauma to the patient’s leg,” explained Ku, who has doctoral degrees in mechanical engineering and medicine. “To avoid these complications, other prosthetic vein valves have been designed, but most have demonstrated poor clinical potential for humans.”

Ku and his collaborators believe the valve they have developed will overcome previous difficulties. The one-way flap is made of poly(vinyl alcohol) cryogel, a material patented by Georgia Tech in 1999. The material has many useful attributes, including its biocompatibility with body tissue because of its attraction to water; the ability to adjust its mechanical strength; flexibility comparable to that of natural body tissue; and composition of organic polymer, rather than silicone.

The researchers will begin conducting preclinical animal trials at Emory University in October to test the in vivo biocompatibility and performance of the prosthetic vein valve prototype in sheep. Sheep were chosen because their cardiovascular geometry and physiology are similar to those of humans.

In each animal trial, two prosthetic vein valves will be implanted by Milner. The researchers will test the biocompatibility and performance of the devices for four weeks, using imaging techniques to check that the valves remain in the proper location, are open and allow blood to pass through the vein.

The animal trials will be conducted after several years of optimizing the valve design and testing it in the laboratory. When the Georgia Tech researchers started designing the valve, they wanted it to be as similar as possible to normal, anatomic venous valves. They focused on two major design criteria: the valve had to withstand high pressures without leaking and the valve had to open with small pressure gradients, even after 500,000 cycles of opening and closing, which is equivalent to a half year.

“It was important for us to test the long-term feasibility of these valves because they’re going to be implanted and used for years,” explained Ku. “But since test methods have not been well established for evaluating a prosthetic vein valve, we developed our own.”

Sathe conducted the initial laboratory tests and found that the valve met the mechanical design criteria – it could withstand pressures of more than 500 millimeters of mercury and opened with a pressure gradient of 2.6 millimeters of mercury, which matched physiologic vein valve function. Detailed laboratory testing procedures and results were described in the June 2007 issue of the Journal of Medical Devices.

Next, Farrell developed a laboratory method to test whether blood clots would form inside the prosthetic valve. Results showed that the new generation of valves remained open with no clot formation after 120 minutes of blood flow, whereas control valves lined with polyester closed up after approximately six minutes of perfusion and showed blood cells adhering to the valves.

The laboratory tests showed that the prosthetic vein valve exhibited low flow resistance, strong competency, fatigue-resistance, low clot formation probability and material flexibility, which allowed the researchers to move forward to the animal studies.

The next step after conducting the animal studies will be human clinical trials. The device will require an investigational device exemption from the Food and Drug Administration so that the device can be used in a clinical study to collect safety and effectiveness data.

“There are 400,000 patients per year who are just miserable with the complications from this disease and could benefit from these valves, so we’d like to help them as soon as possible,” added Ku.

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