Wireless, Implantable Monitors Offer Long-Term Surveillance

Implantable cardiac monitors remain vigilant for rare syncope episodes and heart attacks
By: 
Holly Worth

 

December 13, 2010

In a world where everything is unplugged and cordless is king, cardiology is constantly searching for and developing the technology to make patient care both better and more convenient.

Implantable cardiac monitors (ICMs) are the latest technology on the medical market to satisfy both those qualifications. Invasive and longer lasting than their predecessors, the Holter and loop event monitors, give patients freedom and doctors remote access to syncopal information. This combination results in better diagnosis of cardiac conditions like syncope, atrial fibrillation and other irregularities.

“Before we had this technology, we relied on event monitors that could only function for a max of 30 days,” said Jaymie Hitchcock, director of heart rhythm management department, Mid-America Cardiology, Kansas City, Kan. and Mo. The practice group uses St. Jude Medical’s Confirm ICM, FDA-approved in late 2008. “For patients with syncopes every six months, that’s hard. With this, though, it’s a simple procedure — easy to implant — it can be used up to three years, and it’s automatically recording the symptoms.”

Hitchcock, whose clinic sees a range of patients, said ICMs are not for everyone. Holter monitors, which examine every heartbeat for 24-48 hours, and event loop monitors, which function for 30 days, are tried-and-true recorders for patients with frequent or dependable symptoms.

For patients with rare syncope or presyncopal episodes, however, ICMs are revolutionizing diagnosis and understanding. Blair Grubb, M.D., director of cardiac electrophysiology service, University of Toledo School of Medicine, Toledo, Ohio, sees nothing but those patients in his syncope clinic. For his practice, the development of ICMs has been invaluable. Grubb uses the Medtronic Reveal XT, commercially available since February 2009.

“Previously when doing evaluations, it used to be a leap of faith,” he said. “Now, we can see real-world events as they occur. Now, we see that things are much different than we thought they were. We didn’t fully understand or have a grasp on how [syncopes and other cardiac irregularities] were occurring.”

Syncope can be infrequent, intermittent and seemingly unexplainable. Possible causes include exercise, arrhythmias and other cardiac conditions, and while syncope’s origins are wide-ranging, at least 10 percent of syncope patients’ causes remain unidentified (1). But by evaluating heart rhythm signals over long periods of time, ICMs like the Reveal XT and the Confirm are able to better illuminate the problems to allow doctors to give a more accurate diagnosis.

An Advance Over Holter Technology

Insertable cardiac monitors are meant for different patients, as opposed to their long-established heart-monitoring alternatives. They not only have a longer lifespan, they also utilize different technology. Holter monitors are portable devices connected to the body with electrodes that record electrical signals from the heart. The signals transfer to logging equipment, which attaches to a belt loop or a necklace. ICMs, on the other hand, are approximately the size of a thumb drive, are implanted subcutaneously and require no external wires or patches. Grubb said his experience with ICMs is not only that they work, but also that they’ve gotten better.

“The initial [models] were fairly primitive, but so were cell phones,” he says. “Initially, these had to be patient-activated, but now they record automatically.”

Patient ECGs Available 24/7

Medtronic CareLink Network reads the Reveal XT’s data from a monitor connected to a phone line, which then dials a preprogrammed number to send the information to a Medtronic website. After that, the information is available remotely via the Internet by the physician — at any time and without an appointment. Not only does this make information more accessible, but Grubb said it also gives peace of mind to those fitted with the ICM. “Patients feel reassured to be able to be monitored anywhere in the country,” he said. “It’s like being monitored 24/7 for three years.”

Hitchcock has also seen the benefits of ICMs’ remote capabilities. Confirm monitors connect to the St. Jude Merlin @home Transmitter, which similarly receives information, connects to a phone line and then transfers the data to a website. Remote followups are scheduled daily, often when a patient sleeps. Mid-America Cardiology, which has locations across eastern Kansas and western Missouri, can now consult patients that live five to six hours away. “Having the convenience to ask the patient to send the information from their bedroom and troubleshoot and figure out what’s been going on has made a huge difference,” she said.

Ruling out a heart rhythm irregularity or tracking it is, according to Hitchcock, one of the technology’s greatest strengths. Specialists who deal with syncopal patients, such as Grubb and Hitchcock, are now able, with the help of technology, to better determine the root of the problem.

“The goal of Norman Holter [the inventor of Holter monitors] was to be able to record and differentiate phantom arrhythmias. That was in 1964, and there were always people who were told they were crazy,” Grubb said. “Today, it’s amazing to see events as they actually happen — not as you project them to be and not as you think they are, but as they really are.”

Cost vs. Benefits

Patients suffering from heart irregularities are not likely to see only physical benefits of this technology. Although he cited occasional reimbursement issues, Grubb points to the 2002 randomized assessment syncope trial (RAST) study to show that a prolonged monitoring strategy is more cost-effective than conventional testing in patients with unexplained syncope. And because patients using a monitor like the Confirm or Reveal XT often suffer from rare syncopal events, Hitchcock points out that the one-time cost of inserting a more costly monitor generally outweighs the more-frequent cost of a Holter or loop event monitor.

References:

1. Kanjwal, Khalil et al. “Psychogenic Syncope? A Cautionary Note.” Pacing and Clinical Electrophysiology, July 2009, vol. 32, issue 7, pages 862–865.

Sidebar

An Implantable Heart Attack Alarm

The AngelMed Guardian System is an implantable subcutaneous monitor designed to detect coronary occlusion from thrombotic events, such as plaque ruptures. It alerts the patient, usually before any symptoms occur.

The device, about the size of a pacemaker, was cleared for use in Europe in October. It is implanted the same way as the implantable cardiac monitors (ICM) currently on the market.

Michael Gibson, M.D., chief of clinical research in the cardiovascular division, Beth Israel Deaconess Medical Center, Boston, and a key investigator in a U.S. study of the device, said ST-segment monitoring is like “OnStar for the heart.” By attaching an electrode to the heart, similar to a pacemaker, the system continuously monitors the patient’s electrogram. If a shift in ST segment is detected, deviating from a patient’s normal electrogram, Gibson explained, two things happen. The device implanted underneath the skin will vibrate and a signal will be sent to an external device; both signal to the patient they may be having a heart attack.

Gibson said AngelMed is working on advancing a call center that can respond to alarms and data on the implanted device. Currently, however, the information gathered on ST-segment monitoring devices stays on the device until retrieved and downloaded by doctors. During clinical testing, patients took their symptoms to a doctor or hospital under their own volition, like any other patient experiencing symptoms of a heart attack.

“Until this time, it’s always taken two to three hours for someone to come to the hospital if they’re having a heart attack, even with a second heart attack,” Gibson said. “For every hour you delay, there’s about a 1 percent increase in your risk of dying. The goal was to replace vague symptoms with something that clearly alerts the danger.”
Gibson saw a dramatic improvement with the 40-patient study. “Four patients had the device go off and it only took 19 minutes [on average] for them to get to the hospital” (six, 18, 21 and 60 minutes, according to the study’s results, which were presented by Gibson at the Heart Rhythm Society meeting in May 2009).

But while cardiac specialists and patients are becoming increasingly familiar with and favorable toward ICMs, general practice and emergency department (ED) personnel are sometimes unfamiliar with the devices. “In some cases, the alarm went off and [ED] doctors didn’t believe it. The device had to go off a second time before doctors took them into a lab,” Gibson said. “There’s still a learning curve to get everyone on board.”

  • The Reveal XT comes with the externally carried, wireless Patient Assistant device. It allows patients to hit a record button to capture arrhythmias as they happen. A query button is programmed per physician-identified criteria to enable a status update.
  • The AngelMed Guardian System uses a pacemaker-size implantable monitor as an early warning system to detect coronary occlusion from thrombotic events, such as plaque ruptures.
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