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Internet-Enabled Hearts Run on Wireless
Wireless telemetry puts a new spin on cardiac care
Charles J. Murray, Senior Technical Editor -- Design News, September 1, 2008
Cardiologist Marc Silver was driving to work one morning last winter when he received a page from a defibrillator implanted inside the body of one of his patients. For Silver, it was an unremarkable moment; he had, after all, received such alerts from implanted electronic devices before. But this particular call exemplified the future of medicine better than any he'd experienced.
When he reached his Raleigh, NC office and checked the Internet, Silver learned the electrical impedance levels inside the patient's device had ballooned. He called the unsuspecting man to his office, shut off his defibrillator and, eventually, replaced the device's faulty electrical leads.
“We probably spared the patient an inappropriate shock,” Silver recalls. “And the best part is we didn't have to rely on him to call us.”
Indeed, the advantage of the new breed of smart implantable devices is that they deliver a measure of autonomy to the world of patient management. Using wireless telemetry, microcontrollers, modems and Internet technology, they can analyze heart rhythms, deliver shocks and send information to physicians — all without the aid of the patient.
To be sure, the technology is still in its infancy. Medical electronics giant Medtronic Inc. introduced its Concerto/Virtuoso implantable cardiac devices with wireless capabilities in 2006. In May of this year, Medtronic broadened its program by rolling out a full device portfolio, called Vision 3D. Similarly, St. Jude Medical announced FDA approval of the Merlin wireless RF technology for cardiac devices in July.
It is, in essence, the dawn of a new era — the era of the Internet-enabled heart. Moreover, some say the autonomous care phenomenon could spread to other parts of the body.
“We've had at least 30 patients who have gone into atrial fibrillation and have had wireless alerts notify us,” Silver says. “In all cases, we brought them in and addressed the issue.”
Physicians say such methods are beneficial to patient and doctor alike. “We save patients a lot of trips to the office and that improves their quality of life,” Silver says. “But it's also easier for us to handle a large population of patients when they all don't have to come into the office every time something goes wrong.”
Blazing the Trail
The roots of the remote patent management technology date back to the mid-1990s, when Medtronic engineers began to work with licensing agencies on the assignment of a frequency band for devices inside the body. At the time, they wanted to endow cardiac devices, such as implantable cardioverter-defibrillators (ICDs), with the ability to autonomously communicate their information to tabletop units. Using wireless, they hoped to send the data through the body, across the airwaves and into nearby tabletop transceivers. There, data could be downloaded through the phone connections to servers that would be accessible via the Internet.
Challenges, however, were many. ICDs, which shock an irregular heartbeat back to a normal rhythm, must remain inside the body for years and operate on miniscule power budgets. Moreover, engineers needed to deal with the new issue of sending RF signals through the body, capturing those signals outside and securely storing the data.
For everyone involved, wireless patient management was an adventure in uncharted territory. “There wasn't anyone who had worked on implanting radios and getting information out of the body to an external device,” says Saurin Shah, senior director of communications and systems engineering for instruments at Medtronic.
The starting point for the project was the choice of an RF frequency band. “First and foremost, we knew we needed wireless implementation with very low current consumption,” Shah says. “Wireless is allocated a very, very small portion of the overall power budget for these implantable devices.”
Getting the Data Out
Today, Medtronic solves those challenges by using a little-used frequency band now called MICS (medical implant communications service), which resides between 402-405 MHz on the spectrum. Because it was previously used only by weather balloons and other meteorological aids, the MICS band offers the advantage of virtually no interference.
MICS achieves its communications successes by employing two specific provisions: One is called “listen before talk;” another is known as adaptive frequency agility (AFA). Using those communication schemes, RF transceivers in the system scan available channels, pick the one with the least interference and jump to that.
“Because you're using the channel with the least interference, you have fewer errors and less re-sending of data,” Shah says.
Shah adds that the MICS provisions help the designers in many ways. Low interference translates to more effective use of power, largely because data needn't be repeatedly re-sent. It also provides greater transmitting range: Medtronic engineers say their system officially reaches about 2m of transmission range, but physicians are said to have reported success at greater distances.
Using the MICS band as a foundation, manufacturers are now developing implantable devices and tabletop boxes with onboard radio transceivers. Using metal antennae capable of withstanding the caustic environment inside the human body, the stopwatch-sized defibrillators establish a line of communication with the tabletop units, thus enabling them to share data stored inside the defibrillator's memory.
Preparing for Growth
Medical manufacturers say they foresee a big role for wireless patient management. Since 2001, when Medtronic launched its wireless effort in earnest, the company has boosted the ranks of its engineers assigned to the technology by a factor of eight, from 30 to 240.
The company has also worked hard on developing a secure, easy-to-use environment for physicians who want to take advantage of the technology. Much of that, say engineers, has had to come from the outside — mainly from financial industry, which initially knew more about setting up secure databases.
“Medtronic has always made pacing devices and the physical instruments that support them,” says John Van Danacker, senior director for clinician instruments at Medtronic. “But in recent years, we've had to take that technology out into the clouds of the Internet, which we had never done before.”
Van Danacker says Medtronic also succeeded in this new form of patient management by going to companies with greater expertise in setting up computer databases. “When we started out, we were breaking a lot of new ground, so we worked closely with the likes of Microsoft and others to figure out how to set this up in a secure manner,” he says. “We had to leverage a lot of our knowledge from elsewhere.”
The result is a system known as the CareLink Network, which enables physicians to receive and analyze data over the Internet. CareLink serves as the data transmission platform for the company's wireless telemetry and reportedly allows patients to keep in touch with their doctors from almost any location in the world.
“If a patient is in Iowa or Hamburg or Tokyo, we want to be able to get that information where it belongs, when it belongs there,” says Warren Watson, vice president of implantable product development for Medtronic. “And want to do it without the patient having to intervene.”
Around-the-Clock Surveillance
Medical experts foresee strong growth for wireless patient management. It's especially important for maladies that patients have difficulty recognizing, such as atrial fibrillation.
“The beauty of wireless is that it removes the patient compliance factor,” Watson says. “Many patients who have occasional atrial arrhythmia don't know it. With wireless, their doctor can find out, treat them with the right drugs and possibly prevent a stroke.”
Although it may not have happened yet, engineers say it's theoretically possible for a wireless system to detect a sleeping patient's problem and call a hospital, which could send out an ambulance crew to wake the patient and take him or her to the emergency room.
In the future, experts also say they foresee a day when MEMS sensors will enable such systems to autonomously check for congestive heart failure and ischemia, as well as making measurements of blood glucose levels.
In the meantime, cardiologists say they're content with the ability to remotely manage patients with implantable cardiac devices. The technology, they say, makes diagnosis quicker in critical situations and eliminates the need for individuals to come into the office for frequent device check-ups.
“It's reassuring to know that I've got a surveillance team out there around the clock, watching my patients for me,” says cardiologist Silver. “I wish all my patients had wireless.”
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Internet-Enabled Heart Runs on Wireless
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I find it astonishing that you haven't done your homework. Each of the 3 major medical...
David Cook - 2008-09-04 14:04:38
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