Researchers say the sensor may significantly lower health-care costs and improve quality of life for people with congestive heart failure. The device is one of several prototypes being developed by CardioMEMS and other medical implant companies to provide continuous, personalized wireless monitors for such patients.
"I think the study shows this kind of device is incredibly useful in improving outcomes in patients and directing therapy," says Marc Jay Semigran, medical director of the Mass General Heart Failure and Cardiac Transplant Program, who was not involved in the study.
Hospitals admit 1.1 million adults each year for congestive heart failure, a condition in which pressure builds up in the circulatory system and the heart fails to pump blood adequately to the rest of the body. The American Heart Association estimates that the chronic condition costs the health-care system $29 billion per year. CardioMEMS aims to reduce that figure by providing an accurate way to continuously monitor patients after they've left the hospital.
The device is implanted in the pulmonary artery, an area that carries a low risk of clotting. It is smaller than other implants under development because it does not require a battery or a wire to take pressure readings. Two metal loops hold it to the sides of the artery, and a pressure transducer records the flow of fluids through the blood vessel. The sensor is powered externally by a receiver built into a pillow. When a patient lies on the pillow, the sensor is activated to take measurements and send them wirelessly to a computer, where physicians can review the data. In a large six-month clinical trial published this month in the Lancet, 550 patients from 64 centers across the United States were equipped with the device and instructed to take readings once a day. Patients were divided into two groups. The first took medication instructions from physicians who monitored the sensor data. The second took instructions from physicians who relied on traditional indicators like weight and blood pressure. Over the six months, patients in the first group experienced 39 percent fewer hospitalizations than those in the second.
Today, physicians often assess pulmonary pressure when initially evaluating a patient, but they do so far less frequently in follow-up evaluation. That's because the measurement requires doctors to snake a catheter into a patient's heart and inflate a balloon. However, fluid pressure changes by the day, and monitoring those fluctuations continuously is essential to treating heart failure effectively.
"Over the years, we found that pressures go up long before patients develop symptoms and call a doctor to say they're sick," says Philip Adamson, director of the Heart Failure Institute at Oklahoma Heart Hospital, the principal investigator in the CardioMEMS clinical trial. "By utilizing the pressure sensor information, we're given the ability to make changes in medications long before patients bring themselves to the doctor, and that's how we reduced hospitalizations."
Over the past few years, several companies have jockeyed to be first on the market with a continuous pressure-sensing cardiac implant. In 2007, Medtronic failed to get FDA approval for its sensor, a stopwatch-size, battery-powered implant wired to the heart. The device reduced hospitalizations by 22 percent, but FDA regulators did not consider that worth the risks associated with implanting it. Researchers also found that the wire connecting the sensor to the heart degraded over time.
CardioMEMS is currently seeking approval for its sensor from the U.S. Food and Drug Administration and has submitted results from the clinical study for FDA review. In the next two or three years, the company plans to integrate the sensor's receiver into a patient's cell phone, which will be able to instantly read pressure data and upload it for both physicians and patients to review.