Coronary arteries are susceptible to plaque that can lead to illness, a phenomenon known informally as a “hardening” of the arteries. The effect of this is narrowing of blood vessels. If a clot detaches itself in another blood vessel and does not flow through the constricted section, this prevents blood supply to the heart and can be dangerous or even fatal in some cases. The disease-induced narrowing of coronary vessels and related heart attacks are one of the most common causes of death in industrial nations. Cardiologists use what are referred to as stents to open the closed-up vessels. Stents are tiny mesh tubes that are inserted into the bloodstream via the artery in the groin and placed in the constricted section. The doctors use a balloon catheter to expand the tube. This expands the blood vessel and the blood can flow through freely again. This method has saved the lives of many heart patients, but it does also have one disadvantage: in two of five patients, plaque and growths – referred to as “restenosis” – accumulate again at the place where the stent is located in the blood vessel, leading to a narrowing of the arteries once again. Arteries on the screen In order to understand the processes and the effects of stents in arteries better, Farhad Rikhtegar, a doctoral student from Professor Dimos Poulikakos’ group at ETH Zurich has implanted a stent in a porcine coronary artery in a laboratory, rendered the real internal surface of the artery including the stent in visual form and in mathematical terms and reproduced it exactly. He also created a computer model of the blood flow in the region of the stent. The paper relating to this work was recently published in the journal PloS One.

Rikhtegar’s computer models are realistic and achieve a level of detail that has never been seen before. Older models depicted blood vessels in a simplified manner and took into account only very simple clinical scenarios. However, the simulations by the ETH Zurich researcher are more complex and are based on real-life materials: porcine coronary arteries scanned at high resolution in which stents were implanted. Stents eliminate shear stress The simulations make clear that the tiny mesh-like strut connectors of a stent that lie against the wall of the blood vessel slow down the blood flow along these struts considerably. They also show that the blood in the tunnels formed by the stent struts can be “trapped” in vortices, which also reduces the speed of the blood flow in the vicinity of the stent. Because of the slower blood flow, the shear stress that the blood flow exerts on the wall of the blood vessel decreases. Endothelial cells that cover the blood vessel can only carry out their function properly if the blood flow and thus the shear stress acting on them reach a certain average value. If this stress is too low, they allow more and more bad cholesterol into the vessel wall. This in turn leads to infections that result in atherosclerosis once again. It can happen that the artery narrows once again in the region of the stent. Blind spots create a higher risk of restenosis The simulations also show what can happen if a stent is poorly positioned and does not lie flat against the vessel wall. In such a case, “blind spots” occur between the stent and the blood vessel wall where the speed of the blood flow is also severely reduced, increasing the risk of restenosis. Rikhtegar created further models where two stents, partially overlapping, were inserted into porcine arteries. The risk of restenosis is even greater when stents overlap than in the case of one individual stent. Evaluation of this data is not yet complete, however, and the doctoral student would like to publish the results in another paper. Intricate methodology Farhad Rikhtegar had to be quite creative with ideas on how to create the experiments and the related simulations. He created real-life conditions for the subsequent digitalization process using porcine hearts from the slaughterhouse. In collaboration with cardiologists from the University Hospital Zurich, he implanted the stents into the largest coronary artery. The ETH Zurich doctoral student then prepared the blood vessels by injecting them with resin. After the resin had hardened, he removed the tissue and thus obtained a three-dimensional sculpture of the blood vessels in the porcine heart. This preparation method is not new. However, Rikhtegar optimized the method by developing a pump that pressed the resin into the veins using physiological pressure. He explained that he was still injecting the resin by hand in the first trials. But he exerted too much pressure when using this method, destroying the fine capillaries in the vessels. By contrast, automated injection of the resin into the heart vessels ensured that the detailed meshing of even the finest capillaries was retained. Rikhtegar scanned this resin cast at high resolution with a micro-computed tomographer (CT) from Professor Ralph Müller’s group. This gave him a precise digital presentation of the artery in the vicinity of the stent, through which he was able to allow blood to flow in computer simulations. Normal computed tomography used in clinics and hospitals does not have a sufficient resolution to depict the struts of the stent, which are just 100 micrometres thick. However, micro-computed tomography can provide resolutions for structures of just a few micrometres in size. This allowed Rikhtegar to also present the deformation of the blood vessel wall in a vertical and horizontal direction and to show the position of unfavourably positioned stents. Using the geometry of the vein area containing the stent as calculated by the micro CT images, the ETH Zurich doctoral student was able to carry out simulations for almost any scenario. From aeronautics to medical applications Rikhtegar explains that the work was quite a challenge. There was a specific method for each individual sub-step. In cooperation with the respective experts in the field, the aim was to optimize each of these sub-steps. “That took a lot of time”, says Rikhtegar, who is originally an aeronautical engineer. For his dissertation, he had to acquire specific medical knowledge and learn the corresponding methods. “Now I can even insert stents into coronary arteries – it’s not really that difficult”, he grins. In order to carry out his work, he used around 80 porcine hearts that he was able to get from the slaughterhouse. He used these to test and optimize the different work steps. He then had 15 hearts for the scans and the simulations. The method he has developed is a unique tool that allows for research into the relationship between hemodynamic factors and vascular biology. But the simulation can also be used to optimize the use of stents or to develop new forms of stents and test these on a computer. More information: Rikhtegar F, Pacheco F, Wyss C, Stok KS, Ge H, et al. (2013) Compound Ex Vivo and In Silico Method for Hemodynamic Analysis of Stented Arteries. PLoS ONE 8(3): e58147. doi:10.1371/journal.pone.0058147

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More information: Bleier BS, Kohman RE, Feldman RE, Ramanlal S, Han X (2013) Permeabilization of the Blood-Brain Barrier via Mucosal Engrafting: Implications for Drug Delivery to the Brain. PLoS ONE 8(4): e61694. doi:10.1371/journal.pone.0061694

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Invitation to Attend

The 5th Istanbul Symposium is intended for medical and engineering students, nurses,
scientists, pediatric heart surgeons, engineers, cardiologists, intensivists, neonatologists,
anesthesiologists, neurologists, pediatric perfusionists, respiratory therapists, residents
and fellows. All are invited and encouraged to attend.

Koç University, Engineering Auditorium ( Mühendislik Oditoryumu ) / 19 April 2013

The new translational initiative ‘Science in Practice’ will provide clinicians with insights on where the field is going in the future and basic scientists with a critically important context for future work.

For the first time delegates will be able to follow the “Guidelines into Practice (GIP)” track ,  designed to support cardiologists in the implementation of the Guidelines in their daily practice.

Click for Congress Home Page

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Extended Abstract Submission and Complete Paper Submission: April 24, 2013
Authors Notification: June 17, 2013
Camera Ready and Registration: July 8, 2013

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The microscale electronic sensor monitors blood flow through artificial blood vessels. Surgeons use these prosthetic grafts to bypass diseased or clogged blood vessels in patients experiencing restricted blood supply, for example.

Over time, however, the graft can also become blocked. To avoid complete failure, blood flow through the graft must be monitored regularly, but existing techniques are slow and costly.

Monitoring blood flow rate inside prosthetic vascular grafts enables early detection of graft degradation and prevention of graft failure.

The implant is powered by a handheld external reader, which uses inductive coupling to wirelessly transfer energy. The team developed an ultralow-power application-specific integrated circuit (ASIC) for the implant designed for low-power (21.6 μW) use.

The sensors are based on piezoresistive silicon nanowires. As blood flows over the sensor, the associated mechanical stresses induce a measurable increase in electrical resistance, proportional to the flow pressure.

“Our flow sensor system achieves an ultra-low power consumption of 12.6 microwatts,” said A*STAR’s Jia Hao Cheong, who heads the project. To achieve that the sensor transmits its data to the handheld reader passively, by backscattering some of the incoming energy. “We have tested our system with 50-millimeter-thick tissue between the external coil and implantable coil, and it successfully extracted the pressure data from the implantable device.”

“The next step of the project is to integrate the system and embed it inside a graft for an experimental animal,” Cheong said.

Source: http://www.kurzweilai.net

All rely on catheters—hollow tubes that let doctors burn away and reshape heart tissue or correct defects through small holes into blood vessels.

“This is the replacement for the surgeon’s knife. Instead of opening the chest, we’re able to put catheters in through the leg, sometimes through the arm,” said Dr. Spencer King of St. Joseph’s Heart and Vascular Institute in Atlanta. He is former president of the American College of Cardiology. Its conference earlier this month featured research on these novel devices.

“Many patients after having this kind of procedure in a day or two can go home” rather than staying in the hospital while a big wound heals, he said. It may lead to cheaper treatment, although the initial cost of the novel devices often offsets the savings from shorter hospital stays.

Not everyone can have catheter treatment, and some promising devices have hit snags in testing. Others on the market now are so new that it will take several years to see if their results last as long as the benefits from surgery do.

But already, these procedures have allowed many people too old or frail for an operation to get help for problems that otherwise would likely kill them.

“You can do these on 90-year-old patients,” King said.

These methods also offer an option for people who cannot tolerate long-term use of blood thinners or other drugs to manage their conditions, or who don’t get enough help from these medicines and are getting worse. “It’s opened up a whole new field,” said Dr. Hadley Wilson, cardiology chief at Carolinas HealthCare System in Charlotte. “We can hopefully treat more patients more definitively, with better results.” For patients, this is crucial: Make sure you are evaluated by a “heart team” that includes a surgeon as well as other specialists who do less invasive treatments. Many patients now get whatever treatment is offered by whatever specialist they are sent to, and those specialists sometimes are rivals. “We want to get away from that” and do whatever is best for the patient, said Dr. Timothy Gardner, a surgeon at Christiana Care Health System in Newark, Delaware, and an American Heart Association spokesman. “There shouldn’t be a rivalry in the field.” Here are some common problems and newer treatments for them:

Heart valves

illions of people have leaky heart valves. Each year, more than 100,000 people in the United States alone have surgery for them. A common one is the aortic valve, the heart’s main gate. It can stiffen and narrow, making the heart strain to push blood through it. Without a valve replacement operation, half of these patients die within two years, yet many are too weak to have one. “Essentially, this was a death sentence,” said Dr. John Harold, a Los Angeles heart specialist who is president of the College of Cardiology. That changed just over a year ago, when Edwards Lifesciences Corp. won approval to sell an artificial aortic valve flexible and small enough to fit into a catheter and be wedged inside the bad one. At first it was just for inoperable patients. Last fall, use was expanded to include people able to have surgery but at high risk of complications. Gary Verwer, 76, of Napa, California, had a bypass operation in 1988 that made surgery too risky when he later developed trouble with his aortic valve. “It was getting worse every day. I couldn’t walk from my bed to my bathroom without having to sit down and rest,” he said. After getting a new valve through a catheter last April at Stanford University, “everything changed; it was almost immediate,” he said. “Now I can walk almost three miles a day and enjoy it. I’m not tired at all.” “The chest cracking part is not the most fun,” he said of his earlier bypass surgery. “It was a great relief not to have to go through that recovery again.” Catheter-based treatments for other valves also are in testing. One for the mitral valve—Abbott Laboratories’ MitraClip—had a mixed review by federal Food and Drug Administration advisers this week; whether it will win FDA approval is unclear. It is already sold in Europe.

Heart rhythm problems

Catheters can contain tools to vaporize or “ablate” bits of heart tissue that cause abnormal signals that control the heartbeat. This used to be done only for some serious or relatively rare problems, or surgically if a patient was having an operation for another heart issue. Now catheter ablation is being used for the most common rhythm problem—atrial fibrillation, which plagues about 3 million Americans and 15 million people worldwide. The upper chambers of the heart quiver or beat too fast or too slow. That lets blood pool in a small pouch off one of these chambers. Clots can form in the pouch and travel to the brain, causing a stroke. Ablation addresses the underlying rhythm problem. To address the stroke risk from pooled blood, several novel devices aim to plug or seal off the pouch. Only one has approval in the U.S. now—SentreHeart Inc.’s Lariat, a tiny lasso to cinch the pouch shut. It uses two catheters that act like chopsticks. One goes through a blood vessel and into the pouch to help guide placement of the device, which is contained in a second catheter poked under the ribs to the outside of the heart. A loop is released to circle the top of the pouch where it meets the heart, sealing off the pouch. A different kind of device—Boston Scientific Corp.’s Watchman—is sold in Europe and parts of Asia, but is pending before the FDA in the U.S. It’s like a tiny umbrella pushed through a vein and then opened inside the heart to plug the troublesome pouch. Early results from a pivotal study released by the company suggested it would miss a key goal, making its future in the U.S. uncertain.

Heart defects

Some people have a hole in a heart wall called an atrial septal defect that causes abnormal blood flow. St. Jude Medical Inc.’s Amplatzer is a fabric-mesh patch threaded through catheters to plug the hole. The patch is also being tested for a more common defect—PFO, a hole that results when the heart wall doesn’t seal the way it should after birth. This can raise the risk of stroke. In two new studies, the device did not meet the main goal of lowering the risk of repeat strokes in people who had already suffered one, but some doctors were encouraged by other results.

Сlogged arteries

The original catheter-based treatment—balloon angioplasty—is still used hundreds of thousands of times each year in the U.S. alone. A Japanese company, Terumo Corp., is one of the leaders of a new way to do it that is easier on patients—through a catheter in the arm rather than the groin. Newer stents that prop arteries open and then dissolve over time, aimed at reducing the risk of blood clots, also are in late-stage testing.

High blood pressure

About 75 million Americans and 1 billion people worldwide have high blood pressure, a major risk factor for heart attacks. Researchers are testing a possible long-term fix for dangerously high pressure that can’t be controlled with multiple medications. It uses a catheter and radio waves to zap nerves, located near the kidneys, which fuel high blood pressure. At least one device is approved in Europe and several companies are testing devices in the United States. “We’re very excited about this,” said Harold, the cardiology college’s president. It offers hope to “essentially cure high blood pressure.” Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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