Pulseless Pumps & Artificial Hearts

Pulseless pumps & artificial hearts Mehmet Oz MD Irving Assistant Professor of Surgery Columbia University New York, NY

Patrick McCarthy MD

Surgical Director, Kaufman Center for Heart Failure Cleveland, OH Program Director, Heart Transplantation Cleveland Clinic Foundation Cleveland, OH

LVADs Left ventricular assist devices Portable battery-powered devices that allow hospital discharge are currently being used in virtually all patients. Implanting these devices has become routine; from 1 per month in the early 1990s to 1 per week currently. New implantable LVADs are being developed that are much smaller, continuous flow pumps.

Jarvik 2000 The Jarvik 2000 was implanted at the Texas Heart Institute in April 2000. It is a valveless, electrically powered, miniature axial flow pump about the size of a "C" battery. It fits directly into the left ventricle and pushes oxygenated blood throughout the body

DeBakey VAD The DeBakey heart has recently been approved for use in the US by the FDA. It is a miniaturized axial flow device that pumps blood from the left ventricle through a titanium inflow cannula inserted into the heart's apex. It increases blood flow up to 10 L/min in patients suffering from congestive heart failure. The only moving part is the inducer-impeller; magnets in its blades cause it to spin between 7 500 to 12 500 rpm.

Clinical trials DeBakey VAD Clinical trials began in Europe in November 1998. As of June 8, 2000, 32 patients had received a DeBakey implant. The US has recently received FDA approval to begin clinical trials.

Centrifugal LVADs Rotary centrifugal LVADs have 2 sealed chambers  a pump chamber that moves the blood  a motor chamber which contains the mechanism that drives the pump Power is transmitted between the chambers by magnetism. Two tubes leaving the pump chamber carry the blood between the LVAD and the heart. The third tube to the motor chamber contains the wires to power the unit.

HeartSaver VAD The HeartSaver, weighing about 500 grams, is a fully implantable device for long-term use that can be remotely powered, monitored and controlled using TET and biotelemetry technologies. Its shape follows the contour of the chest wall and connects via short conduits to the apex of the left ventricle of the natural heart and to the ascending aorta. It is intended for long-term circulatory support and recipients are expected to leave the hospital and resume near normal day-to-day activities.

TET coils Power supply The TET (transcutaneous energy transmission) system transfers electrical energy through the user's intact skin and tissue to directly power the implanted VAD and the implanted, internal back-up battery.

Permanent LVADs Advantages  better quality of life  eliminates the need to take immunosuppressive medications The transition to more permanent LVADs will be gradual.

LVADs The durability and engineering of the pumps is much better than it was. Our understanding of heart failure management has advanced, with innovative new drugs and surgical reparative approaches. To tailor our therapies, we need to better understand the impact that immunology has and the way patients with artificial devices respond to foreign bodies. The most commonly used pump today owes its success in part to the fact that it prevents anticoagulation.

Design challenge Pulsitile flow It was first thought that the lack of pulsitility with axial flow pumps would have some impact to the body. However, the first cases from Europe using the Debakey pump have shown that this isn’t the case. In a few isolated instances pulsitile flow may be important (e.g., in the case of a traumatic insult to an organ for which optimal conditions are required for full recovery). However, for the average daily existence, it is probably not necessary.

The heart Not just a pump This very complicated field is still in the earliest phase. The heart is not just a pump, it is also a neuroendocrine organ. There are signs that the heart recovers, which opens the possibilities for adjunctive therapies to LVADs like angiogenesis factors, myoblasts and growth hormone.

Selecting patients Bridge to recovery The inability to predict who will have a sustainable recovery has led to the practice of leaving pumps in. The biochemistry of the heart may help us understand why an individual cell of the heart stops carrying its workload, why it doesn't process fatty acids, or why it doesn’t take up calcium the way it once did. Dealing with these underlying metabolic problems may help us make these recoveries sustainable Once response to treatment can be predicted, heart devices can be used as a bridge to recovery instead of a bridge to transplant.

Abiomed Total artificial heart The Abiomed total artificial heart is a biventricular assist device implanted inside the chest to replace the heart. Whereas the LVAD is only for the left side, the artificial heart is for both sides. The Abiomed total artificial heart uses a centrifugal pump to move silicone hydraulic fluid, which drives the device. A sleeved, rotating valve shuttles the fluid between the left and right blood pumps.

Biventricular support Candidates  patients who are plagued with continuing moderate rate heart failure on the LVAD  patients with ventricular arrhythmias that may inhibit their recovery while on an LVAD alone  patients who have very severe right heart failure  patients who have ventricular arrhythmias  patients with acute MI complicated by such things as a ventricular septal defect

Stroke prophylaxis It is very difficult to predict from animals what the stroke rate is going to be in humans. Caution and some anticoagulation will probably be the recommended course of action to begin with.

HeartMate device An electrically powered device, which, unlike the LVAD, does not need a vent to the outside. The current LVADs have a vent that allows the air to go back and forth as a pusher plate moves inside the device. Risk of stroke with the HeartMate device is extremely low.

Progress report With the Jarvik-7, it was hardly worth living because quality of life was so low. LVADs Today's LVADs are portable and patients are discharged from hospital. Total artificial heart Patients will be discharged with battery powered devices that have a low risk of mechanical failure. It is expected that risk of stroke will also be low.

Ideal candidates Total artificial heart Patients who have end-stage heart disease; a patient population similar to the heart transplantation group. People who have a very limited quality of life and length of life because of their heart disease but who do not have other major organ limitations. Not patients who are in their 80s, who have end-stage diabetes and numerous other organs with complications.

LVAD as a bridge Candidates  patients with ventricular arrhythmias on LVAD support  patients for whom LVAD isn't adequate  patients who have had failed heart transplants, whether there is transplant coronary disease or some type of refractory rejection  patients who have lymphomas related to the immunosuppression

New developments In various stages of development  8 axial flow pumps  2 artificial hearts

Media attention The idea of using devices for supporting the heart is becoming more accepted. Economic issues will probably be the most controversial topic. Leading role for investigators Emphasize the importance of basing conclusions on the first 100 patients, not on the first patient.

The next step Cardiac support The next step in cardiac support will never be heart transplantation. Heart transplantation can only supply 2200 hearts per year. Mechanical devices are things that will have epidemiologically significant impact on cardiac support