An Implantable Heart-Attack Monitor

A pacemaker-like device aims to get victims to the hospital faster.

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.

Heart alert: An implantable device, shown bottom right, measures a heart’s electrical activity. The device transmits information to an external device (the black box with cable), which tells the patient if he needs to visit the emergency room. This device transmits data to the physician’s workstation (the white box with screen), which tells the doctor what happened during the attack. Credit: AngelMed

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."

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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.