The National Institutes of Health has prematurely terminated a clinical trial testing two techniques designed to improve survival when paramedics treat heart attack victims, concluding that neither one provided any benefit. One trial tested how much CPR paramedics should perform before determining whether the patient needed to be defibrillated (shocked) to restart his or her heart. The second tested the efficacy of a device called an impedance threshold device or ITD that had been shown in animal trials to increase blood flow to the heart during CPR. About 11,500 patients already had been treated during the trial, and the researchers concluded that enrolling more would not change the results.
CPR performed by paramedics is a combination of chest compressions (to pump blood through the body) and rescue breathing. Lay people are encouraged to use only chest compressions until paramedics arrive.
Paramedics treat about 350,000 people with cardiac arrest, in which the heart stops beating, in the United States each year, but fewer than 10% of patients survive. In the majority of cases, the patient's heart had simply stopped beating for too long before paramedics were summoned and arrived. But health officials had hoped the new techniques could provide some improvement in survival rates.
In one arm of the trial, paramedics performed CPR for only 30 to 90 seconds before checking to determine whether defibrillation was indicated. In the other arm, they performed it for at least three minutes before checking. Small trials have given different results, with some showing that a short delay is better and others showing the long delay is preferable. But the new trial's Data and Safety Monitoring Board concluded that neither was more effective than the other. "Both techniques appear to be equally beneficial," said Dr. Ian Stiell of the Ottawa Hospital Research Institute in Canda, the principal investigator.
The ITD is a small hard-plastic device, about the size of a fist, that is attached to the face mask or breathing tube during CPR. It is designed to improve circulation by enhancing changes in pressure within the chest during CPR. In animal studies and small studies in humans, the device was found to markedly increase blood flow to the heart and raise blood pressure. Researchers had hoped that would improve retention of neurological function in patients who survived. Some patients whose heart stops for prolonged periods have severe neurological impairment that interferes with their quality of life.
In the trial, patients were randomized to receive either the ITD or a nonfunctional device that looked the same. Researchers found that survival was the same in both groups, as was retention of neurological function, suggesting that standard CPR was as effective as CPR with the device.
Patients in both arms of the trial will be studied for another six months to determine if there are any long-term effects.
-- Thomas H. Maugh II
Photo: An instructor teaches CPR. Credit: Los Angeles Times