Building Better LVADs
Less a Bridge Than a Destination?
Editor's Note | Eman Hamad, MD, Medical Director, Mechanical Circulatory Support Program at Temple University Hospital, provided important review and oversight for this editorial.
"He can’t come to the phone right now because he is patching the roof.”
That was the comment I received from the wife of a patient who had end-stage heart failure, and 8 weeks before my call he had a left ventricular assist device (LVAD) implanted to support his heart while awaiting heart transplantation. At our institution, we started our LVAD program as a bridge to transplantat in 1994, using the bulky pulsatile LVADs that were implanted in the abdomen but provided normal cardiac output, allowing patients to resume a life not limited by severe impairment of exercise capacity.
The first VADs were driven by a pneumatic system with tubes penetrating the skin of the abdomen to drive the diaphragm of the pulsatile device. The driver was large and needed to be wheeled around, confining the patient to the hospital while awaiting a donor heart. The technology quickly evolved to an electrically driven LVAD that had the drive motor incorporated into the device; the only skin penetration was for a wire to deliver power to the LVAD. The patient could carry several battery packs, making the whole system readily portable, meaning the patient could leave the hospital and live at home while waiting for a transplant.
In 2001, the REMATCH trial showed that patients not waiting or ineligible for a heart transplant would benefit from an LVAD as the definitive therapy for their end-stage heart failure, thus forming the basis of “destination therapy.” Now, given evidence of structural and molecular changes that improve cardiac function after LVAD implantation, there is interest in studying these devices as a bridge to recovery.
As with most mechanical systems, we saw a constant effort to improve the technology. The biggest step was to move from a pulsatile LVAD to a continuous-flow device that was much smaller, more durable, less noisy, and better tolerated by the patient. The device was modeled around rocket fuel injectors that contained a high speed rotor turning at more than 2,000 rpm that could pump 6 or 7 liters a minute. The device could be implanted in the thorax and electrically driven, but despite being better tolerated by the patient, those of us caring for these patients had some important learning to do. We needed to adapt to the concept that the patient had no pulse—as well as to concerns when care providers, not familiar with the device, tried to measure a blood pressure and got no result. We know that the blood pressure in an LVAD patient is a mean blood pressure, so setting the device to generate a blood pressure of 120 mm Hg would actually make the patient severely hypertensive. A mean systolic blood pressure of 80 to 85 mm Hg is usually what is established; it is measured with a Doppler probe and the LVAD patients learn how to use the probe to assess their blood pressure.
We also noted an increased incidence of gastrointestinal bleeding in patients with a continuous-flow LVAD. After much investigation, this appears to be related to breakdown of von Willebrand factor (VWF) as blood contacts the high speed rotor. The components of VWF cause arteriovenous malformations in the gut that eventually bleed (acquired von Willebrand disease).
In spite of several limitations, the continuous-flow LVAD has established itself in the armamentarium of therapies for end-stage heart failure. Patients are able to resume near-normal lives, don’t require hospitalization, and in many cases return to work. But there is more work to be done. Because there is a limited supply of donor hearts for transplant, and a much greater number of people with end-stage heart failure, the LVAD will continue to be a valuable therapy. Technical improvements are still needed. Eventually, an induction charger will be developed that will charge an implanted battery to avoid skin penetration and the resultant infection risk. A smaller LVAD that supplements rather than replaces the entire cardiac output will be applicable for many patients who have some residual left ventricular function and don’t need a 6 to 7 l/min flow capacity.
With the pulsatile LVADs, we learned to listen to the LVAD sounds to detect failure of the bearings in the pump. With the axial, continuous-flow devices, we hear only the soft whine of the rotor spinning at 3,000 or 4,000 rpm, and the floating bearings are resistant to failure, so durability has extended from 1 to 2 years with the pulsatile LVADs to more than 5 years with axial LVADS. As we move forward with the technology, the demand for assist devices will grow due to the aging population and our ability to avoid mortality in many patients with severe heart disease.
Thus patients with LVADs will truly become part of our population of heart patients. Managing these patients will require special care and special knowledge to understand the physiology and complications of LVADs. At the same time, we now can provide a tool that will allow patients severely disabled by end-stage heart failure to resume a near normal life.
Alfred A. Bove, MD, PhD, is professor emeritus of medicine at Temple University School of Medicine in Philadelphia, and former president of the ACC.
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