Typical patient needs the pump's help for less than a week
An investigational heart pump may enable people with severely weak hearts to recover from needed heart surgery. Cardiac surgeons at the University of Maryland Medical Center in Baltimore are the first in the region to implant the new type of pump, which is designed to give the heart a short-term rest after cardiac surgery. The device, the Abiomed Impella 5.0, has been implanted in three patients at the medical center so far, as part of a four-center, 20-patient pilot study. The first Maryland patient, a 43-year-old man from Germantown, needed just two days on the pump to restore a strong heartbeat after he had double coronary bypass surgery and a procedure to correct an abnormal heart rhythm.
The device has been approved for use in Europe, where more than 250 patients have been treated with it. The pencil-sized pump assists the left ventricle, the heart’s main pumping chamber, and is designed to function for about one week. In some cases, it can be deployed without a large incision. The U. S. Food and Drug Administration has approved a less powerful version of the Abiomed device and a similar pump from another manufacturer.
“We are evaluating this device for patients whose hearts are weak and need some support after heart surgery,” says the national study’s principal investigator, Bartley P. Griffith, M.D., chief of the Division of Cardiac Surgery at the University of Maryland Medical Center and a professor of surgery at the University of Maryland School of Medicine. “The small pump, designed to fit inside a catheter, can be placed through an artery into the heart. This technology is an indication of where the future of heart-assist devices may be headed,” says Dr. Griffith, who is a pioneer in the evaluation and development of a variety of mechanical support devices for the heart.
John McCarthy, the first patient to receive the Impella pump at the University of Maryland Medical Center, developed major symptoms of heart distress in June 2007. “I started having shortness of breath and swelling of the legs,” he says. Doctors found a blood clot in a lung and coronary artery blockages.
In July, he came to the University of Maryland Medical Center where doctors determined that his heart was pumping at only 15-to-20 percent of normal. “About 80-to-85 percent of Mr. McCarthy’s blood was staying in his heart. It didn’t have enough strength to squeeze the blood out,” says Sina L. Moainie, M.D., a cardiac surgeon at the University of Maryland Medical Center and an assistant professor of surgery at the University of Maryland School of Medicine.
Besides the coronary artery blockages, Mr. McCarthy also had a type of arrhythmia called atrial fibrillation. An abnormality in the electrical conduction system of his heart caused an irregular and ineffective heart beat. His surgical team performed a bypass procedure to increase blood flow to the heart, and also performed a procedure called CryoMaze to correct the atrial fibrillation.
Because his heart output was already reduced and the stress of surgery would likely reduce that output further, his surgeons decided to use the Impella. According to Dr. Moainie, “When you have heart surgery, you may have a short term drop in pumping ability because of the stress of surgery. Medicines can usually control this drop, but because Mr. McCarthy’s output was already so low, medicine alone would likely not be adequate for him.” Dr. Moainie adds that after two days, in most cases, the inflammation and swelling usually associated with cardiac surgery disappears, and the benefits kick in.
To gauge how well the heart is pumping blood to meet the needs of the body’s organs, doctors look at a measurement called a “cardiac index.” Dr. Moainie says the minimum acceptable cardiac index is two liters of blood per minute. Mr. McCarthy’s cardiac index immediately after surgery and before the pump was implanted was 1.7, despite the use of two different medicines to help the heart squeeze better. That level of output is less than necessary to sustain life. When the pump was removed two days later, his cardiac index had improved to 3.4 without the help of any medicines. “Not only had his heart gotten better, but it has also sustained that good performance,” says Dr. Moainie.
The Impella is the smallest device available for left ventricular pumping. It weighs only eight grams, but can do the work of much larger ventricular assist devices, pumping up to five liters of blood per minute, about three-quarters of a normal heart’s output of seven liters per minute.
The respite that the pump provides can be enough for the heart to bounce back to normal. That appears to have happened to John McCarthy despite his brief time on the device. “I feel 100 percent better,” he says. “I have no shortness of breath. I had leg swelling before and now it’s going away. Every day I feel like I’m getting stronger.”
Two other patients received Impella implants at the University of Maryland Medical Center after Mr. McCarthy, who was on the pump in July 2007. One required the pump for three days before it was removed, while the second patient was on the pump for eight days.
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