Can a human survive with no pulse? It's a long-standing argument that one prominent heart surgeon is seeking to prove in his efforts to develop a total artificial heart that produces a continuous, pulseless blood flow.
The future of artificial heart development to treat people with deadly congestive heart failure may lie in this simpler design one that eliminates the need for a pulse.
"Since the introduction of the heart/lung machine, there's been controversy about how important a pulse is for circulation," said O.H. Frazier, MD, chief of Cardiopulmonary Transplantation, chief of The Center for Cardiac Support, and director of Surgical Research at Texas Heart Institute (THI; Houston) and director of Transplant Service at St. Luke's Episcopal Hospital (Houston).
"My position is that the only thing that needs a pulse is the heart itself," he told Medical Device Daily. "The blood that is delivered everywhere else pulseless. This was an ongoing debate. But more and more, we've gotten interested in continuous flow because it offers an opportunity to replace function of the heart with a device that's much more user friendly than pulsed devices."
Frazier, who is reported to have performed more heart transplants than any other surgeon in the world 1,000+ said the big advantages of this proposed cardiac device are size, durability and cost. The National Institutes of Health (NIH; Bethesda, Maryland) has just awarded THI a $4.1 million grant so that Frazier and his team can continue their work to determine the effects of pulseless blood flow on bodily functions.
Continuous flow pumps were first introduced for partial support of failing hearts, but they have never been used for total heart replacement. Currently available artificial hearts are expensive, often too big to fit most patients and last just a few years.
"A continuous, pulseless blood flow heart, we think, will last 15-20 years," he said. "There are no valves, so it's potentially much less expensive."
Frazier has been working on hearts since he as a medical student in the 1960s. Just two years ago, he took a heart out of a calf and replaced it with continuous pumps.
"The animal woke up fine," he said. "Since that time, we've been very interested in it as a total artificial heart replacement. It's been very gratifying that these experimental animals tolerate this very well. Hopefully we can learn much more. We do think there is a need for long-term reliable cardiac replacement that will render a patient capable of living a normal life."
In the new THI study, calves' or sheep's hearts will be replaced with two small, continuous flow blood pumps that operate according to the principle of centrifugal force. Compared to existing assist devices, the new total artificial heart will function more like a natural heart, in that it can adjust how much blood it pumps depending on how much blood is in the heart.
Being able to assess how the device responds to the body's changing needs for blood is a key objective of the study.
"We're working with engineering groups to see if we can determine some way of working on responsivity of the pumps," Frazier said. "The other advantage of continuous flow pumps is that their flow is increased by increasing inflow pressure much like the native heart, which only increases output if it needs more blood. These pumps will do the same. There are instances where we'd like to increase the RPM. In clinical pumps we've used, we could only run them at a fixed rate and haven't cracked the code on that yet. We're also going to look at microcirculation in non-pulsatile animals."
He said a pulse may be necessary for some people, particularly those with atherosclerosis.
"They may need a pulse to wash out the blockages in the arteries," he said. "By varying the speed, we could induce a pulse. In this study, we may be able to come to some conclusion about the role and utility of inducing pulsativity. The effects on the arteries will be studied."
Frazier said that, until a few years ago, nobody else was working on this theory. After a presentation of his early findings at a medical conference, four other groups have since emerged that are working on the same theory, one the U.S. at the Cleveland Clinic as well as teams in Japan, Berlin and Australia.
"People are skeptical at first, but once they realize the possibilities, everybody wants to get involved," he said. "It's important to have other people working on it. You need a certain critical mass of people, particularly at the outset."
Anecdotally, Frazier said he's had five patients with no heart function supported by continuous flow pumps. They went into ventricular fibrillation, but were fairly well supported by the pumps.
"I've heard of another colleague of mine who replaced a heart with one pump and the patient is doing well. So we've already seen that it works in a physiologic sense," he said.
Currently, his team is using commercially available pumps, but new technology is needed for a total heart replacement.
"These grants are not for product development, but we need something like what was done for LVADS [left ventricular assist devices] in the 1970s and 1980s," he said. "That would be the next important step. I would encourage device makers to get involved. Nobody I know is actually working on it. We've definitely established long-term survival without a pulse is not only feasible, it's desirable if we're making something to replace the heart. Now the technology will be the next challenge."
In addition to his team at THI, Frazier is collaborating with Thoratec (Pleasanton, California), Beth Israel Deaconess Medical Center (Boston) and Harvard Medical School (Boston).
Lynn Yoffee, 770-361-4789; firstname.lastname@example.org