A New Application in Cardiac Monitoring: Interview with Dr. John Messenger
John Messenger, MD, is the medical director of the Cardiac Care Unit (CCU) at MemorialCare Heart and Vascular Institute. In this interview he describes his use of the AngelMed Guardian® system at Long Beach Memorial Medical Center, as well as his involvement in the ALERTS clinical study. The AngelMed Guardian system, which is currently available for investigational use only in the U.S., is an implantable cardiac monitoring and alerting system designed to warn cardiac patients of potentially life-threatening heart conditions.
Explain how the AngelMed Guardian System works. What are the components of the system?
The AngelMed system uses a device, similar in size to a pacemaker, which is implanted in the left pectoral region of the chest and has a lead with an electrode to the right ventricle. If there are ischemic changes of significance, an algorithm in the AngelMed Guardian system will identify these electrocardiographic ST changes and alert the patient. It is the same as a positive treadmill test or abnormal EKG, but can be identified much earlier in many patients. To notify the patient, the device will give either a “911” signal, which directs the patient to immediately go to the ER or call the paramedics, or a “Call your doctor” signal, which is a different signal pattern that originates with the implanted device and is sent via telemetry to a hand-held telemetry device carried by the patient. In addition, the signal provides an audible as well as vibratory ring under the skin, so if the patient has difficulty hearing, they can still sense the vibration and know when to call a physician. So that is a basic explanation of what happens if a patient has ischemia but no demonstrable sensation of chest pain.
In what patients is this system most beneficial for?
In diabetics, there is a problem associated with not having proper sensing of pain, so when they experience a heart attack, they often present without severe discomfort. Since the population is made up of at least 25 percent of patients with diabetes, they are the more identifiable patients who would benefit from this type of device. For patients with clotting disorders or other problems that tend not to be typical or predictable, this system gives these patients early warning so they can get to their physician before damage to their heart occurs.
Tell us about the ALERTS study at Long Beach Memorial Hospital. In how many cases have you implanted the AngelMed Guardian System?
We’ve been involved in the study for a little over a year. It is a randomized control study, which means that half of the patients receive the full-featured device. The other half, referred to as the control group, receives a fully-functional device as well; however, the patient alerting feature is turned off for the first six months, and after 6 months, the alarm is turned on. In the meantime, we continue monitoring, and if for some reason there are concerns regarding an event that occurs, we monitor the patients very carefully and perform nuclear studies during the time to be certain that we’re not missing something during the control period.
The purpose of this study is to prove that the system is beneficial. Already, several patients who have had heart problems were alerted by the device within the first year of implantation and subsequently revascularized. I believe that for all of these patients, if not for the device, we would not have detected the severity of their coronary disease in terms of the changes from the previous studies. Most of these patients were high risk — we’ve done either coronary angiograms, general stress tests or nuclear studies on all of them to show that they did have ischemia. However, several of them had previous surgeries and it was not quite clear because of the multiple bypass grafts as to where the specific area of ischemia was. Thus, these were more complicated cases, and that is why we chose the AngelMed Guardian system. I think in general, patients do not have proper warnings for heart conditions, and the solution for what to do for them is not quite as obvious as you’d like on a standard angiogram.
Is the device usually implanted in the cath or EP lab? How is it inserted?
We do the implants in our EP pacing room. It is implanted like a pacemaker in the left upper chest, below the clavicle. The single electrode is advanced into the venous system across the tricuspid valve into the right ventricular apex in the bottom of the heart, which is the area where initial electrodes most likely pick up abnormal changes from all areas of the left ventricle and have been proven over history to be the central area. For example, it correlates well to standard treadmill leads 4, 5, and 6, which would be the chest leads near the bottom of the heart to the left of the sternum, which is where the signals emit from.
How is the AngelMed Guardian System different than other implantable monitoring devices?
There are no other implantable monitoring devices like this. It’s a little bit like a radar system that can see over the horizon — the device can see a problem before it is clear to the patient or doctor.
A number of centers have opened over the last few months in the U.S., but there are only a few of us that have been using the system for a year or more. However, I feel that there have been enough patients saved by this system that it is more than worth it in these specified cases.
Does the Guardian system also detect abnormal heart rhythms such as ventricular tachycardia?
Absolutely. As I mentioned earlier, there are 2 warnings — the first warning is when there is not enough blood getting to the heart, which is the 911 warning. During the 911 warning there is a very distinct buzz in the chest on the left side where the device is, which transmits to a telemetry receiver and alerts the patient. The other warning is the “Call your doctor” warning, which alerts patients of arrhythmias.
When is the ALERTS study expected to be complete?
I’m not totally certain. However, from our limited experience, it has proven to be very useful already in the small patient group of 10 that we’ve had here.
Is there anything else you’d like to add?
I know some of the pacemaker companies have been interested in perhaps incorporating this type of warning system into other sophisticated devices. In fact, St. Jude Medical has incorporated the AngelMed Guardian’s detection algorithm into their AnalyST Accel and Fortify ST ICDs, which are currently available in Europe and Japan.
There are a large number of potential patients, most of them somewhat older, who could potentially develop coronary artery disease. With this technology they could have the advantage of patient comfort and possible prevention. I think that is a very exciting potential for the future and would go hand in hand with the development of this type of device.
There is no other device like this available. I’ve been director of the Coronary Care Unit for 35+ years, and during that time there have been no implantable or placeable devices with any capability of detecting the electrocardiographic changes coming from the heart without the patient first triggering it after chest pain. This speaks to the issue, that we are implanting this in patients who 1) experience either no chest pain at all (primarily diabetics), or 2) patients with such atypical pain that it would be an advantage to them to know if this discomfort they’re having is coming from their heart. That is the subset we’re interested in treating and getting this care to directly.
Patients with pacemakers and ICDs frequently have coronary artery disease as well. That is a pretty significant market for managing care, and we’re seeing more and more of these types of patients arrive in the coronary care unit, generally not as early as they should. Therefore, they end up having more heart damage, in some cases, fatal damage, because there is no real warning. What the AngelMed Guardian system does is offer us the ability to apply the new engineering principles of angiographic interpretation in treatment for acute ischemia.