Researchers seek success with mechanical pumps
Can devices span CHF, recovery?
The day is coming, researchers say, when mechanical pumps will offer CHF patients a range of options for improvement and recovery.
Refinements continue to be made in using left-ventricular assist devices (LVADs) as a bridge to transplantation. Investigators now want to find out how they can offer the devices to more patients — such as those who are not transplant candidates because of their advanced age or degree of heart disease.
And today’s tantalizing but rare cases of patients being weaned from their LVADs hint at a time in the future where doctors can use a pump to let a failing heart rest and heal until it can work well on its own again.
Getting to these goals, and crossing what some doctors call "a bridge too far," means pushing the limits of the technology and running the trials. Investigators are optimistic.
"You might decide that today’s pumps are not right for you and your patients," says Mehmet C. Oz, MD, an LVAD researcher and cardiothoracic surgeon at Columbia-Presbyterian Medical Center in New York City.
"With the advances being made, you should see a pump that’s right for you within a decade," he explains.
Buying patients more time as they await transplantation is a huge niche for LVADs to fill. Recent published reports determine only 2,500 organs are available each year to some 60,000 patients who need them or some type of mechanical help. In 1996, more than 10% of the transplantation candidates died waiting for a new heart.
What about those not up for transplants?
Oz says doctors should be thinking about when LVADs may be appropriate for their patients today, whether or not they’re on the transplant list.
"The first rule of thumb is that no one should die of heart failure without being considered for heart pumps."
That doesn’t mean giving one to every patient, Oz notes, but rather, thinking about how a patient can be treated with an LVAD after traditional therapies are ruled out with a line of questioning such as the following:
1. Does the patient have a problem that can be repaired, such as aortic or mitral valve disease or an aneurism?
2. If there isn’t a physical defect that can be targeted for repair, can the patient’s heart failure be controlled with medication?
3. If medication cannot keep the patient’s condition stable, could transplantation be implemented to reverse the patient’s declining cardiovascular performance? (In this case, a heart pump can help sustain the patient until a permanent organ becomes available.)
4. If the patient is not a transplantation candidate, could an LVAD be used? (Today, patients can be part of the clinical trial testing the devices when other options are not appropriate or can no longer be helpful by themselves.)
This last consideration may not sit well with some doctors, who may feel that if a patient is not up to the surgery and recovery from transplantation, he or she would not benefit from using an LVAD.
Oz says his team is learning how LVADs can be helpful to these patients. The researchers have a $7 million government grant for their REMATCH study (Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart failure). He says patients have to apply to participate in the study, but for those who are not transplant eligible, an LVAD may provide a treatment option.
How long on an LVAD?
Two end points in heart pump therapy are crystal clear:
• transplantation
• infection requiring removal
In other cases, knowing when to stop using the LVAD is not as certain. Oz says there will be a growing number of patients not going on to transplant who will continue with their device, incorporating other treatments such as surgery and drug therapy to improve their heart performance.
Researchers also are looking at the chances of using the LVAD to help the patient’s own heart recover enough to work on its own. This role is called a bridge to recovery.
In 1997, German investigators reported in Circulation (1997; 96:542-549) that they were able to wean a third of their 17 patients from their LVADS.
"We haven’t been able to reproduce their results," Oz says. In a recent article in Circulation (1998; 98:2,383-2,389), his team reported a retrospective study and an explanation evaluation that used exercise tolerance as an indicator of success.
The team found that among 111 LVAD recipients being bridged for transplants since 1991, only five were explanted. In three of these instances, the devices were removed because of infection. The other two patients had their LVADS removed because they were not going on to transplantation: one after 186 days and another after two years.
Of these five explant cases, two died three months after explantation. Two patients needed reimplantation after being without them — one after two years, the other after 170 days. The fifth patient was still alive in class I CHF after 15 months without the device.
In the second part of the study, 39 recent LVAD recipients were considered for explantation, according to how well they could exercise with their LVAD output reduced to 20 cycles per minute. Seven of the 39 patients were able to exercise at this rate of assistance and still keep stable hemodynamics. One was able to be explanted.
Oz says the Germans’ success may be due to the way Europeans wean their patients off the LVAD three months after implantation. The practice may be a good idea because researchers still have a lot to learn about how the heart responds to its mechanical helper and how long the partnership should last.
It’s possible that patients reach a point where the heart pump no longer works well with the compromised heart. A device could even cause atrophy in the heart muscle, depending on its synchrony with the ventricle as it contracts and relaxes.
Research will bring more uses for device
More research is needed, Oz says, to determine how long a patient should use the heart pump, whether or not weaning should begin, and how weaning should be done.
Right now, he says his team does not implant LVADs with the intention of weaning patients off of them. Nearly all the heart pumps used now are bridges to transplantation. Oz notes he recently had a case where a patient had a massive heart attack and an LVAD was used as part of his overall treatment, but those situations are not as common.
Other physicians see three standard uses for an LVAD, including helping patients who suddenly run into trouble, says Ross Zimmer, MD, a Philadelphia cardiologist with the joint heart failure program at Presbyterian Medical Center and the Hospital of the University of Pennsylvania.
These uses are:
• A device can sometimes help patients who suffer complications during surgery.
• An LVAD is used as a transplantation bridge (the most common use).
• LVADs are used in a clinical trial.
The editors commenting on Oz’s study in Circulation note they hoped clinicians would one day be able to assess how a failing heart has been damaged on a cellular level — and whether the damage is reversible. This would give clinicians an indication of which hearts may go on to heal if given some mechanical assistance.
Oz says it would be even more helpful to understand the cellular changes of the heart so they can be reversed long before treatments like heart pumps are needed. Answers may come from looking at how patients may not be metabolizing free fatty acids or calcium properly. Harvesting heart tissue from deceased CHF patients could allow scientists to probe the mitochondria and hunt for missing or defective genes, which could lead to a whole new arsenal of cardiovascular genetic therapies.
Until that point, doctors say LVADs have a role in treating CHF.
"I hope that as [LVADs] become more common, they are developed not just as a bridge but as an alternative to transplant," says Jim Fitzpatrick, MD, clinical assistant professor of medicine in the division of cardiology at Thomas Jefferson Medical Center in Philadelphia. "The economics are staggering."
He says last year, Jefferson implanted two LVADs into CHF patients as bridges to transplantation. The site is not a transplantation center, so the patients continued with treatment at other centers to get new hearts.
And patients can find some reassurance when they learn that LVADs can help during the wait for a heart, says Zimmer: "It’s nice psychologically for patients to know that it’s there."
Editor’s note: For more information about the LVAD study and to learn how to become involved, call (888) REMATCH.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content