In a study published last year in the New England Journal of Medicine, researchers found that 58 percent of patients who received the HeartMate II LVAD survived for at least two years with the device. Previous research shows that conventional therapy, on the other hand, has a 25 percent survival rate at one year and an 8 percent rate at two years.
LVADS are sometimes used as a bridge to recovery if doctors expect the heart may get better. But in Cheney's case, "that's unlikely to happen" because of prior damage to his heart from previous heart attacks, according to Abraham.
"It may be a bridge to transplantation," he said. "At 69, he is still within the age range of eligibility if medically he is otherwise reasonably fit," he said. "Some programs at Ohio State routinely consider [transplants] through the age of 70 and with medically pristine candidates into their mid-70s."
But the waiting time for heart transplants can be "quite long," said Abraham.
"The virtue of the LVAD patient is that he is deemed to be quite sick and because of that the priority level goes up a bit," he said. "But even with that, the waiting time can be many months or years. With the LVAD, patients can survive to transplant and it keeps them alive and in pretty good shape."
"We have no idea if they are considering a transplant on him," said heart surgeon Gardner. "We would think he could last, treated with this LVAD, for weeks or months, assuming he does not suffer other complications with the device."
"If he is on a transplant list -- and we don't know this -- he could wait weeks to months," he said. "But I wouldn't think he is an ideal candidate because of his age and the fact that he had a poor heart condition which can lead to other problems."
In 2001, Cheney had a pacemaker installed in his chest, and last September, he underwent elective back surgery to treat lumbar spinal stenosis. He spent three days in the hospital at the end of June for treatment for fluid retention related to his coronary artery disease.
He received IV medication and his health "markedly improved," his office said a day after he was admitted.
At the time, Cheney said that it became clear that he was "entering a new phase of the disease" when he began to "experience increasing congestive heart failure."
"After a series of recent tests and discussions with my doctors, I decided to take advantage of one of the new technologies available and have a Left Ventricular Assist Device (LVAD) implanted," he said in a statement.
At the moment, the HeartMate II is the one LVAD commonly used for long stretches of time.
Older devices tended to have more limited life spans. After 16 to 18 months, some patients had strokes, bleeding and infections -- all potential risks with ventricular assist devices.
"The device can provide up to 10 liters per minute of flow," said Dr. Keith Aaronson, medical director of the Center for Circulatory Support at the University of Michigan, who has been an investigator on several of the devices.
The normal heart "pumps five liters per minute at rest, but we increase that with exercise, or with other physical activity," Aaronson said. "This device also can increase the flow it provides in response to increased activity. As you do more, more blood flow returns to the right ventricle. The pump responds to that and pumps more out to the rest of the body."