Does Dick Cheney Have a Pulse?

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Former Vice President Dick Cheney, 69, who underwent surgery last week to implant a pump to assist his heart, may be only one step away from a heart transplant, according to cardiac experts. They say he could find himself on a wait list for "months or years."

Cardiologists say the former vice president has a left ventricular assist device (LVAD), which is often used as a so-called "destination" or permanent device, but in his case is likely a "bridge" that will keep him alive until he can receive a transplant.

VIDEO: Dick Cheney Gets a Heart ImplantPlay

Many patients with such pumps are described as not having a pulse, because the continuous flow of the LVAD -- much like water circulating in a fish tank rather than pumping like a heart -- can make the pulse indiscernible.

But heart experts say that only patients who depend on LVADs for 100 percent of their circulation are essentially without a heartbeat. Cheney's device is likely doing 30 to 60 percent of the heart's work.

"The HeartMate II is used in situations where the patient's native heart continues to pump, but not normally and effectively," said Dr. Timothy J. Gardner, a heart surgeon at Christiana Care Health System in Wilmington, Delaware, and past president of the American Heart Association.

"But it's enough to have some detectable pulse, " he said.

The LVAD is implanted next to the heart to help its main pumping chamber, the left ventricle, pump blood through the body. Such devices are used mainly for short periods, to buy potential transplant candidates time as they await a donor organ.

"It's a really good strategy," said Dr. William Abraham, director of the division of cardiovascular medicine at Ohio State University, which does 75 to 100 implantations a year.

"It's reserved for people who have end-stage heart failure, and advanced and heroic therapies have been tried, and after folks have optimized evidence-based and guideline-recommended drug therapies," he said. "Their heart conditions have progressed to a state where the mortality risk is very high and they turn to LVADs and transplants."

Cheney's doctors said his operation went well and he is now recuperating.

The surgery took place at Inova Fairfax Heart and Vascular Institute in northern Virginia.

The reason he did not go to his usual medical home at The George Washington University Hospital is that LVADs are only implanted at two area facilities: Inova Fairfax and Washington Hospital Center.

Cheney has a long history of heart problems. He has had five heart attacks, the first in 1978 when he was just 37 years old, and the fourth in November 2000, after he and former President George W. Bush were elected to the White House.

"We know that he has severe ischemic coronary heart disease that has done a lot of damage to his left ventricle," said Abraham. "It's been described as a relatively small pump and [doctors] have implied he will be up and fully functional soon. That makes sense that it's an LVAD. Other devices are far more intrusive and the recovery is much slower."

The device pushes blood from the left ventricle into the ascending aorta -- the beginning of the major blood vessel that supplies the rest of the body.

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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.

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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."

Implantation of the LVAD is "major surgery," according to Aaronson, and patients are hospitalized, on average, for three to four weeks.

The pump is placed in the abdomen. It is connected to a controller outside the body, a small unit (6 inches long, 3 inches high) that's generally worn on one's belt.

The LVAD can be powered by external batteries, or, while they recharge, a power pack with a 20-foot cord that allows mobility, said Aaronson.

The main risks are blood clots, which can cause disabling strokes in about 12 percent of cases. Other problems reported are hemolysis, or damage to red blood cells from the force of pumping; and infection or bleeding.

LVADs are used in patients with end-stage heart failure -- heart failure does not improve with other medical therapy. It's typically called New York Heart Association Class IV Heart Failure.

These are patients "with very limited life spans -- the threshold is different at different centers. In general, though, these devices are used as destination therapy in patients who have a 50 percent or higher risk of dying in the next six months. Quite frequently, these patients are likely to die in the next days to weeks if the pump is not implanted," Aaronson said.

But for some, the device buys more time than they could have expected.

"We have a patient now who is over 5 years," said Aaronson. "That patient had to have the device replaced after 4 years."

ABC News Medical Unit researcher Jane E. Allen contributed to this report.