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State-of-the Art in Artificial Hearts Copyright 2001 Info

Page 2 of an interview with cardiothoracic surgeon, Mehmet Oz, MD,
New York-Presbyterian Hospital, NY, NY.

By Sean Henahan, Access Excellence

In the first section of this interview we discuss the early days and current status of LVADs, left ventricular assist devices that are implanted to assist the weakened hearts of patients with heart failure. In the following section we discuss Abiocor, a new artificial heart that is now ready for human trials.

The FDA recently approved a new artificial heart device for human trials called Abiocor. Can you tell us about that?.

A: The Abiocor system is an exciting alternative to VADs. There are patients who have failure on both left and right side of heart, or who have other problems that limit the use of LVADs. In that setting we had no choice but to let the patient die. There is now for the first time a totally implantable artificial heart that could potentially allow us to implant a device that allows patients to live for a long period of time. This is a new, well-designed device. The design tales advantage of the fact that the right and left sides of the heart don't have to pump blood at the same time to provide compliance between each chamber. The company also designed a battery system that allows transcutaneous electrical transfer. This device has combined many of the lessons we have learned with VADs and other heart devices about the management of critically ill patients. This device could offer a new option to a lot of people. While no human has yet received one of these devices, there have been many cows operated on with considerable success. There's no question in my mind that the device will be implanted in the near future. The real decision for us will be to decide how many will need the device. We don't really know what percentage of people that we couldn't help with LVADs we would be able to help with the total artificial heart.

This was tried before with the JARVIK7. That product marked the end of research in that area for quite a while. What has happened since to encourage another try?

A: The JARVIK7 experience early on was probably too big a step. It was actually a success to the extent that the scientists proved they could replace the human heart and keep patient alive with an artificial heart. However, the device did not provide the quality of life that most of us would want. For that reason the American public soured on the thought that you can use high technology to build a bionic man The experience with JARVIK7 killed interest in this area for almost a decade. It took a long time to rekindle an interest in these device and convince the public that we were not creating a Frankenstein, but instead developing an option that might be viable for our loved ones. The Abiomed system is well designed and I don't think we will fall into those pitfalls. However it will be challenged by several factors. First, there is the LVAD that can provide support for some patients. Patients will be faced with a choice. They will usually choose based on the maturity of the system. So it is important the Abiocor be used and become a mature, patient friendly system. Of course it will depend how well the device delivers what it needs to- high quality of blood pushed through the body without a high incidence of stroke or infection.

How did the developers overcome the previous limitations seen with JARVIK7?

A: There were three big challenges to overcome. One, we need a surface material that would allow blood to flow without a high thromboembolic (clotting) incidence; two, we needed a mechanism for having the blood be ejected from one chamber without needing a big compliance chamber within the chest; third, we needed a battery system that could power this device without risk of infection. One by one these were addressed.

The Abiomed company created one of the first LVADs. It is perhaps the most commonly used one in US today. But it is only used for short-term support, as a bridge to transplant. One reason they are popular is the very slick surface, made of a coating compound that we believe reduces the incidence of stroke. As a physician I like to use the pump, but only for a couple of days. The same coating is used in the Abiocor heart. We had to make up for the fact that the left and right heart don't actually pump the same amount of blood all the time. We had to make up for that difference. This device takes this into consideration. Finally, we had to solve the power problem. Battery supply problems have plagued all VAD systems. The creation of TETS is a novel innovation that allowed the creation of a 'wireless' artificial heart. This is an experimental device, not a panacea. These devices, as with previous devices, are likely to be fraught with early failure. There will be people who will die directly as a result of these pumps not working perfectly. Unfortunately there is no way to know until we try the pumps. The measure of success initially will be more a matter of how do we respond to these problems, to continue to develop the system so that it will be successful for a majority of patients.

The main problem with all implantables has been the increased risk for stroke. How do the new devices address this?

A: Device surfaces have improved dramatically. The one used in the Heartmate device is remarkably resistant to thromboembolism. It tricks mother nature with a very rough surface. If blood going by sticks to the surface, it can't come off again. This means this stuff cannot chip off and cause problems like stroke. In addition to new surfaces, there are improved anticoagulation systems. As we understand more about how platelets function we can target anticoagulation a bit better. The reality is that it is a much more global picture. When you put a machine in a man, it is not just the machine you have to understand or the man, you have to understand the man/machine interface.The machine changes the way man responds to stressors including infection and stroke. You have a diffuse inflammatory process which is associated with the coagulation process, creating a prothrombotic (clot-inducing) milieu. You are asking for trouble. A better understanding of the man/machine interface will help us to prevent these problems.

Biological research has made incredible progress in recent decades. How have advances in the basic sciences affected cardiovascular research?

A: The heart was a black box 50 years ago. If you saw the heart the patient would die. Some surgeons thought it would be malpractice. This was still the case when aviator Charles Lindbergh developed one of the first heart pumps in the 1950s. At that time the heart surgeons were developing ways of stopping and restarting the heart, while on the medical side, cardiologists were pioneering ways of diagnosing heart disease. The two fields have now met, with very little gap between them. Research has defined some of the pathologies that kill people with heart disease. It also helped us to better understand the physiological functions that alter as we age and develop coronary and valvular disease. Without an understanding of why these things were happening we really could not address the big problems. Probably the biggest benefit over the last decade is that we have moved from an autopsy-based model of understanding the heart, where we used to look at the heart after the patient died to figure out what was wrong, to developing techniques to understand the physiology of the living heart. For example, we can now look at the plaque in the heart and identify the active plaque more likely to close off an artery, more likely to cause an heart attack. That is when we can intervene. Not when the guy is already dead.

There is no question that the headline grabbing features we see in mechanical heart devices today would never have come to fruition had it not been for the ability to build a broad based approach to managing heart disease. It starts in the basic sciences, and not just in universities and world famous research labs. It starts in middle and high school science classes where people receive the initial training. This creates the basis for subsequent interaction between basic science researchers and clinicians to create the applied research endeavors that creates these pioneering projects such as VADs and artificial hearts.

This interview was conducted by Sean Henahan on February 27, 2001

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Dr. Mehmet Oz

Dr. Mehmet Oz

 

Abiocor artificial heart


Above: The Abiocor Artificial Heart System

 

 

 

FACTOID
Your heart pumps blood through a network of 60,000 miles of vessels.

Source- Mayo Clinic

 

 

 

Jarvik Heart

Above: The Original JARVIK Artificial Heart

 

 

 

FACTOID
Heart disease is the single largest killer of Americans- claiming some 950,000 lives in the United States each year.

Source- American College of Cardiology

 

 

 

 

 

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