A surgical team from the University of Central Florida College of Medicine and Arnold Palmer Hospital for Children, Orlando, has presented findings from the first study to demonstrate that the way a ventricular assist device (VAD) is implanted can have an impact on whether or not a patient may have a stroke while the device is in use. Specifically, the surgeons reported that they can adjust the way they implant a VAD to align with a patient's thoracic anatomy and as a result, modify blood flow patterns so that blood clots don't travel to the brain and possibly cause a stroke while the VAD is in use. This landmark study on stroke prevention in heart failure patients was reported at the 2010 Annual Clinical Congress of the American College of Surgeons.
The surgeons reconfigured the angles along which they would sew a VAD into the heart based on a magnetic resonance imaging scan of a patient's heart, aorta, and aortic arch (the main blood vessels that come out of the heart). Using computerized simulations of blood flow, the surgeons determined, for each surgical configuration, the size and percentage of blood clots that entered the two carotid arteries (arteries that carry blood to the brain). At one extreme, one of the configurations had an 18 percent average rate of embolization (blood clots travelling to the brain). At the other extreme, a configuration had an 8 percent rate of embolization.
The computerized technique, which is known as computational fluid dynamics, produces numerical simulations, not tests on actual patients. However, the surgeons applied the simulations to a real patient's aortic anatomy. "We took a patient's MRI scan and recreated the flow through it down to a fraction of a millimeter precision through computational fluid dynamic modeling. So a very real patient's anatomy went into very precise simulations as a starting point. Then, we calculated the pathway of blood clots forming within the VAD and travelling along the aorta," said William M. DeCampli, MD, PhD, FACS, a professor of surgery at the University of Central Florida and chair of surgery at the Arnold Palmer Hospital for Children in Orlando.
The surgeons are theorizing that "we could conceivably lower the stroke rate following the implantation of a VAD from 20 percent to 7 percent by making a surgical maneuver which is not that difficult to make," he explained.
At the ACS Clinical Congress, the surgeons showed videos of blood flowing through a VAD and the path taken by blood clots formed on the interior of the device. "We will demonstrate that as you change the angle of implantation of the VAD, the blood clots will tend bypass the carotids and travel down the descending aorta. So instead of embolizing to the brain, the clots embolize more peripherally where one would hope potential damage would not be so severe," Dr. DeCampli said. Furthermore, by using patient specific MRI data, each patient could potentially be prescribed a unique configuration in which to implant the VAD.
Findings from this study, in fact, suggest other surgical procedures during VAD place-ment that could further reduce stroke risk. "While we found that clots could be directed away from one carotid artery, they tended to go up the other carotid artery," Dr. DeCampli said. The solution to this problem would simply be to use a graft to bypass the other carotid artery. "With the simulations, we're finding that without a whole lot of extra surgical work, surgeons could place such a graft in a suitable location to ensure blood flow to both carotids and prevent embolization of blood clots," he said.
VADs are implantable mechanical pumps that direct blood from a small conduit connected to the left side (ventricle) of a heart that is failing to the aorta. VADs take over the work of the ventricle and pump blood to the body.
VADs are used to manage patients with end stage congestive heart failure by providing a "bridge" to receiving a cardiac transplant. The devices also are being applied as destination therapy or continuous, long-term support of failing hearts. "We now have evidence that patients can live with an acceptable quality of life with an implanted mechanical VAD in lieu of a transplanted heart," Dr. DeCampli reported.
Stroke is the most frequent serious complication following VAD implantation. The annual risk of stroke varies between 10 percent and 47 percent. Efforts to reduce the incidence of stroke have focused on altering the surfaces of the devices so the mechanical elements are not considered to be foreign bodies by the immune system and do not cause blood to clot. Alternatively, stroke prevention has focused on the use of blood thinners, or anticoagulants,
that prevent clot from forming. Neither approach has been very successful.
The surgical team from the University of Central Florida are following a different avenue of research. Rather than try to prevent blood clots from forming, "we just assume the blood clots will form. We're trying to modify blood flow patterns so the clots will not go to the brain," Dr. DeCampli concluded.
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