An implantable device that alerts high-risk patients when they show signs of a heart attack could shorten the time it takes for the wearer to seek medical attention. The device, being developed by AngelMed, a medical-devices company in Shrewsbury, NJ, is already approved for use in Brazil and is now undergoing clinical testing in the United States. While early tests show that it can detect heart attacks, the impact on a patient’s long-term outcome is not yet clear: tests of other cardiac devices have found that detecting problems earlier doesn’t always translate into better health for patients.

AngelMed’s device, called the Guardian, is similar to other implantable cardiac monitors, such as defibrillators. Leads are attached to the patient’s heart to record the electrical activity of the muscle. While existing devices are designed to detect electrical problems in the heart, known as arrhythmias, the Guardian uses novel algorithms to detect problems with blood flow in the heart–the hallmark of heart attacks. Specifically, the device detects something called segment elevation, which causes an abnormality in the electrical current during the time that the heart is recharging between beats.

“Patients often take almost three hours to come to the hospital for a heart attack, and that number hasn’t budged much despite patient-education efforts,” says Michael Gibson, chief of clinical research in the Division of Cardiology at Beth Israel Deaconess Medical Center, in Boston, who is overseeing part of the clinical trial. “Every hour you delay in getting to the hospital increases risk of dying by 1 percent. We feel very strongly that if we can get that time down, we can get risk down.”

A similar approach is used with external electrocardiogram machines in hospitals–in which sensors are placed on the skin–to detect heart attacks. But Gibson and his collaborators found that assessing electrical activity directly from the heart is much more sensitive and can detect changes much more quickly.

When the device detects signs of heart attack, it generates a buzz that the patient can feel on the skin. A receiver outside the body, which wirelessly receives data from the implant, then tells the patient if the problem is severe–meaning he needs to go to the hospital immediately–or if it requires a more leisurely office appointment. “You can bring the device to the ER and show the doctor what was happening when the alarm went off,” says Gibson.

So far, more than 40 patients in the United States and Brazil have received the implant. In the first phase of testing, two patients had a heart attack during the trial, both of which were detected by the device. Researchers are now enrolling patients for a larger trial of 600 to 800 patients. The trial will focus on high-risk patients, such as those who have already had a heart attack.

“I think there is lots of potential for these types of devices,” says William Abraham, director of the division of cardiovascular medicine at Ohio State University, in Columbus. Abraham has done extensive testing with an implantable diagnostic device from Medtronic that monitors heart rhythms.

However, some experts are skeptical that the AngelMed device will make a significant difference in a patient’s clinical outcome. “There’s no question that the earlier you get treated, the better off you are,” says William Maisel, director of the Medical Device Safety Institute at Beth Israel Deaconess Medical Center, who is not involved in the clinical trials. “But the vast majority of patients develop symptoms, such as chest pains or shortness of breath, when they have a problem. The idea that we need an early-warning system–I just don’t see it.”

Maisel adds that patients who have already had a heart attack–the most likely candidates for the device–are also the most likely to recognize and quickly respond to symptoms.

The issue of clinical impact has plagued previous cardiac diagnostic devices. In 2007, a Food and Drug Administration panel recommended against approving an implantable monitor developed by Medtronic to detect heart failure. While clinical trials showed that the device accurately measured intracardiac pressure, which signals when the heart isn’t pumping enough blood, having that information did not significantly reduce the number of patient hospitalizations or ER visits due to heart failure.

However, Maisel says that two groups in particular may benefit from the AngelMed device: people who have heart attacks and don’t feel them–a disorder called silent ischemia that can occur in some diabetics with nerve damage– or “people who have frequent chest pain but not heart attacks, and go to the emergency room unnecessarily.”