When asked to describe a human body, one usually says: head, neck, torso, arms and legs. Oh, but it’s so much more that that, isn’t it? From earliest times man has tried to understand what’s it made of and how it works. As technology progressed, he discovered the complexity of this biological marvel which even today continues to amaze and surprise. We understand the human body as a very complex machine and, like any machine, it breaks and needs fixing. We’ve learned to repair and replace many of the human body parts, including the one that keeps it running: the heart.
The heart is a fist-sized muscle that beats 100.000 times a day pumping the blood through the veins, constantly supplying the body with oxygen and nutrients and removing harmful metabolic waste. Being identified as not only the engine but also the center of the body, it would be wise to take care of it.
Due to unhealthy diets and the lifestyle in these industrialized societies, heart disease became the number one cause of death for man and women, claiming more than 7 million lives per year around the world.
Researchers and doctors came up with so many solutions to control the symptoms of heart disease, from medicine to surgical techniques that help to re-establish the functionality of a heart. Devices such as defibrillators and pacemakers were created to help people with heart disease. But the only way to cure heart failure is a heart transplant. However, the number of donors is not a very large one and patients suffering from severe heart disease may not survive the wait for a new heart. So, researchers thought about replacing it. They created a mechanical artificial heart powered by an external battery, that pumps the blood and keeps a healthy blood-flow through the body. The artificial heart is a device usually destined to replace a broken heart until a healthy one is available for transplant. If that is not possible, the artificial heart can be a permanent replacer of a human heart.
A bit of history
Although devices were invented and attempts have been made in this direction since the 1960s, it was in 1982 that a man received the first permanent artificial heart at the University of Utah. The Jarvik-7, created by Willem Kolff and Robert Jarvik, was successfully implanted to a 61 year old dentist named Barney Clark who survived for 112 days. Later, in 1985, the second Jarvik-7 heart was implanted. The patient, Mr. William Schroeder lived 620 days. Several other patients received the Jarvik-7 heart over the next year, but Mr. Schroeder was the longest survivor.
In 1990, after the Jarvik-7 became Symbion, 198 artificial hearts have been implanted to patients.
In 2003 the Jarvik-7, which was previously renamed CardioWest, was taken over by SynCardia Systems Inc. and for over 30 years the SynCardia temporary Total Artificial Heart has been used for bridging human heart transplants with a 79% rate of success.
Dr. Jarvik’s research gave birth to many other companies that continued to develop temporary Total Artificial Hearts (TAH), and progress has been made in terms of effectiveness, safety and also in reducing the size of artificial hearts.
In 2001 Abiomed implanted to a patient the first AbioCor. It was the first TAH to have an internal power source. The internal battery which lasts for half an hour can be recharged through the skin with help from a four hours lasting external battery. With no wires or tubes piercing the skin, chances of developing infections decreased. Although progress has been made, the implanted device was not without flaws. It was still too big and suited only for larger males, and could only be used for one or two years. However, it’s design proved to be very helpful for patients with critical heart failure who were not candidates for transplant.
In 2006 Berlin Heart created an artificial heart which was implanted to a 15-year-old girl. Although the intention was to be a temporary implant until a donor heart was found, the implanted Berlin Heart assisted the occurrence of a natural process of healing on the girl’s heart. After 146 days the Berlin Heart was removed and a transplant was no longer needed as the heart’s functions were back to normal.
Another contributor to artificial heart development is Carmat who designed a prototype made of animal tissues. It was implanted in 2013 to a 75 year-old patient who survived for 75 days after surgery. The Carmat design can control the blood’s flow rate with help from a sensor that detects increased pressure (when a patient exercises, for example), which makes it different than previous designs that kept the flow rate constant. The Carmat artificial heart is rather used as a permanent implant for patients with end-stage heart failure than a bridge to transplant.
The heart of an adult weighs around 250 and 350 grams. Recent artificial heart designs are much heavier and larger than that. For example, the AbioCor replacement heart ($250,000) weighs 1,090 grams and the Carmat artificial heart ($181,000-$233,000) weighs 900 grams. These sizes makes the devices suitable only for large patients, so the search for solutions is still on.
Do we need a pulse?
Whenever you gently press your wrist, you feel a barely perceptible movement called pulse. That is the sound of your heart. The designs of artificial hearts, be they temporary support or permanent replacers, mimic the native heart. They create a similar blood flow and they give a pulse too. The question is: do we need a pulse? This is not a recent question to pop in someone’s head.
In 1976 Dr. Richard Wampler was on a field trip to Egypt when he saw two workers using an Archimedes’ screw to pump water up a river bank. An Archimedes’ screw is a big spiral in a tube. By placing the tube in water and rotating the spiral, water is scooped up.
So Dr. Wampler thought that this might be a good way to pump blood. When he returned home he designed a small metal version of the screw, about the size of a pencil eraser, and he attached it to a plastic tube. His thought was to spin the screw fast enough so a meaningful amount of blood could be pulled out of the failing heart through the tube and through the body. This device became known as the Hemopump, and it was the first continuous flow pump in the world. It was first implanted to a 61 years-old patient with heart failure. After 2 days he was discharged from the hospital, as the pump successfully sustained him.
Over the next decade several devices were created following this design. They became durable, self contained for longer term implantation, they allow patients to go back to full active lives, they are much smaller than the pulsatile pumps and they are simpler since they only have one moving part.
Based on Dr. Wampler’s design, Abiomed created Impella, the smallest heart pump, about the size of a pencil. It has a very small motor inside the device at the end of a catheter. It was FDA approved for clinical use in 2015 and it can support the heart for periods up to 6 hours.
In 2011, after more than 3 decades of research in transplantation and heart surgery, Dr. Frazier and Dr. Cohn transplanted the first continuous flow artificial heart to a 55 year-old man, at the Texas Heart Institute. The heart of the patient was removed and replaced with two customized HeartMate II LVADs (left ventricular assist device). He became the first living person without a pulse or a heartbeat. This was a big departure from bio-mimicking and proved that life can be sustained without the need of a pulse.
But how could we tell if a person is dead or alive if there is no pulse? And if we have artificial hearts, does that make us heartless? What do you think?