Healing a Broken Heart
At 60 beats per minute, a suction noise representing a thumping heart is emitted from Room 3128 of the USF medical building.
Inside, an intricate system of tubes and cylinders represents the functions of the human body, powered only by a 12-volt DC battery source. A pulse monitor nearby measures a pressure wave to simulate the beats of a heart.
This left-ventricular assist device, commonly known as LVAD, has been in the works at USF for about 12 years, though it has yet to be implanted into a human. Its purpose is not to replace an entire heart, but to assume the pumping responsibilities of a human’s left ventricle. However, if two LVADs were combined, a complete artificial heart would be created.
According to Dr. Leo Ondrovic, lab director for the artificial heart program at USF, the heart transplant of Barney Clark in the 80s led to a decline in funding for artificial hearts. But media coverage of the transplant of an artificial heart into an unnamed patient this summer at the University of Louisville has led to a renewed interest in the subject.
Due to a lack of funding, the USF artificial heart program became idle about five years ago. Though a team has been recently resurrected, it is still without funding at the moment. The goals of the LVAD include offering a permanent replacement for a failed heart or providing a temporary replacement until a heart transplant could be maintained. It is also proposed to use the LVAD as a temporary device by taking the pressure off of a heart as it naturally heals repairable damage, although this has not been tested.
The USF LVAD operates by electromagnetism. One wall of the device holds a magnet, and the opposite wall contains an electromagnet. An electric current engages and repels a magnetic field, which attracts and detracts the walls of the device, creating a squeeze, or a pulse. The diaphragm, or portion of the device containing the electromagnet, is the only part of the LVAD that moves, with the exception of the two valves.
“Because it’s a fairly simple device, it’s easy to replace,” Ondrovic said.
According to Ondrovic, the simplicity of the device is extraordinarily important for its reliability. For example, the Abiocure artificial heart implanted by the University of Louisville is run on a motor, and if one spring on the motor fails, the entire device would fail.
“The number of moving parts is directly relational to how reliable something is,” Ondrovic said.
Additionally, if the LVAD were to be implanted, the position of the device would be irrelevant due to the ability of the magnets to work at any position.
Dr. Michael Van Ocker, who joined the team last September and is working on improvements in the design of the LVAD, said the heart is comparable in size to an average human heart, and would therefore be easy to transplant. Ondrovic proposes the heart could fit anyone from a small 100-pound woman to a large 250-pound male.
“We tried to make the pump as small as possible,” Ondrovic said. “But obviously there’s a limit.”
The device is made from Vivathane, a type of polymer (plastic-like material) created at USF. According to Van Ocker, this polymer is the only substance that would come in direct contact with a patient’s blood.
“One of the problems (with alternate substances) is that they tend to induce clotting,” Van Ocker said. “This particular polymer is very compatible with blood so the effects are minimized.”Although the artificial heart team is not currently working directly on the LVAD, they are presently developing a controller for the LVAD to make the device completely automatic. Because a 12-volt DC battery currently powers the device, the team is experimenting with ways to manipulate the power supply.
According to Ondrovic, at this time it is thought that a patient would wear a belt containing a battery pack as a power supply, which would conduct electricity through the skin to the device through plates on either side of the skin.
The team is currently getting ready to prepare proposals for funding of their research. Ondrovic said they will attempt to propose to foundations such as the American Heart Association, the National Institute of Health and possibly even corporate sponsors such as Abiomed, which funded the research for the University of Louisville.
Along with researching and experimenting with the heart, the team has come across certain ethical issues and is sure to encounter more as experiments continue. Ondrovic said in this particular project they will encounter debates dealing with issues such as animal testing and patient rights and consent.
Before the artificial heart program was disbanded, the LVAD had been tested on sheep and cows. Ondrovic said animal testing is necessary in order to ensure success and so the heart can be tested in a human subject.
The next step after the group receives funding will be to implant the device for long term use in an animal, which they expect to be a calf.
“The only real way to determine if something will work in a real-life setting is to use animals,” Ondrovic said. “But it has to be done humanely and provide scientific information.”
The team will also have to face issues dealing with the patient, such as informed consent, who will receive the device and the task of making sure the patient doesn’t feel pressured.
“It’s so you’re not taking advantage of the patient, who is part patient, part experimental trial,” Ondrovic said.
When the LVAD is ready for human testing, potential candidates for the heart would be those who have permanent heart failure without any other options. Further restrictions would be decided later.
The length of time the LVAD would prolong a person’s life ultimately would depend on the individual application. Ondrovic expects the LVAD to be a temporary stay, prolonging life for a few years, but an actual artificial heart would be expected to prolong life for 30 to 40 years without failure.
In the meantime, Ondrovic said they are building up to their goal.
“We’re trying to be conservative in our approach,” he said.
“You don’t go for the brass ring on the first try; you try to work up the ladder.”
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