The loss of mental sharpness suffered by many heart-bypass patients several months after surgery may not be caused by the heart-lung machine used in the operating room after all, a study suggests.
The research found that mental decline also occurred in bypass patients who had been put on a newer device that does not require stopping the heart.
Tens of thousands of bypass patients each year suffer mental decline after surgery, including difficulty thinking and remembering. The condition may not show up for several months and can last for years. One leading theory is that the heart-lung machine is the culprit.
The Dutch study compared results in heart-lung machine patients with those put on an "off-pump" device that only partially immobilizes the heart. Off-pump patients had less mental decline than heart-lung patients at three months, but the differences became negligible a year after surgery.
The Dutch researchers said one possible explanation is that the off-pump device might also contribute to mental decline. But they also theorized that anesthesia, used in both procedures, or the trauma of surgery itself might affect mental functioning.
American Heart Association spokesman Irving Kron, a University of Virginia cardiologist, said the study adds to the mystery.
The study appeared in the Journal of the American Medical Association.
In an accompanying editorial, Drs. Daniel Mark and Mark Newman of Duke University called the results inconclusive. They said that patients in the Dutch study were generally younger and healthier than the typical U.S. heart-bypass patient.
Heart-lung machines are used to put oxygen into the blood and circulate it. The heartbeat is stopped with medication, and a thin tube is inserted into the aorta during the procedure.
Many doctors believe the machine can dislodge tiny bits of fatty plaque from diseased arteries, or cause tiny blood clots or air bubbles to flow to the brain and cause strokes or other brain damage.
Studies have shown off-pump devices have fewer complications and involve shorter hospital stays, but the effects on mental decline are unclear.
About 571,000 heart-bypass operations were performed nationwide in 1999, 10 percent with off-pump devices. That portion has climbed steadily and is projected to reach 50 percent by 2005, according to Mark and Newman.
The Dutch study involved 281 patients at University Medical Center in Utrecht, where an off-pump device called the Octopus cardiac stabilizer was invented. The device uses two small suction pods to immobilize a small part of the heart during surgery. The university gets royalties from the worldwide sale of the device, which is marketed by Medtronic.
Patients underwent mental tests before and after bypass surgery. Three months after surgery, 21 percent of off-pump patients showed mental decline, compared with 29 percent of heart-lung patients. At one year, mental decline was present in nearly 31 percent of off-pump patients and 33.6 percent of heart-lung patients, a negligible difference, the researchers said.
The editorial noted that elderly people in general are prone to mental decline after major surgery, and not just after heart bypass operations.