Removing doubt: Implantable ST-segment monitor can eliminate delay in MI treatment

May 6, 2010 | Reed Miller From Theheart.org

San Diego, CA – An intracardiac ST-segment monitor, which alerts patients to significant ST shifts indicative of thrombotic occlusion, reduced patients’ “alarm-to-hospital” time from the typical two to three hours to less than 20 minutes in early studies.

Results of the first two pilot studies of the AngelMed Guardian implantable ischemia detection system (Angel Medical Systems, Shrewsbury, NJ) were presented as a poster here at the Society for Cardiovascular Angiography and Interventions (SCAI) 2010 Scientific Sessions by Dr David Holmes (Mayo Clinic, Rochester, MN), who said that the results will also soon be published. Angel Medical sponsored the studies.

“The problem is that patients often deny the symptoms or confuse the symptoms with GI distress or something like that,” coinvestigator Dr C Michael Gibson (Beth Israel Deaconess Medical Center, Boston, MA) told heartwire. “This makes it very clear that you’re having a heart attack. There’s no confusion about that, and there’s no denying it.”

The AngelMed Guardian is implanted like a pacemaker or ICD. It monitors the intracardiac electrogram, acquired at 200 Hz with a band pass of 0.25 Hz (2-pole) to 48 Hz (5-pole), from the tip of a steroid-eluting pacemaker lead placed at the right ventricular apex.

A total of 37 patients at high risk for acute coronary syndromes were implanted with the device in two studies—17 in the Brazilian CARDIOSAVER study and 20 in the North American DETECT study. Over the follow-up period (median 1.52 years, range 126-974 days), with a total of more than 58 patient-years and 18 million monitored electrogram segments, no patient had a ST-elevated MI, cardiac death, or Q-wave MI that was not detected by the device.

Four patients’ devices alerted them to a demand-related ischemia, an ischemic event during or following an elevated heart rate, indicating the emergence of a flow-limiting coronary obstruction similar to what is seen with exercise stress testing.

Four patients had supply-related ischemic events, in which the monitor detected a significant ST shift during normal heart rates. Following additional 12-lead ECG monitoring at the hospital, these patients underwent angiography or intravascular ultrasound, which confirmed the presence of a thrombotic coronary occlusion or ruptured plaque. The median alarm-to-door time for these four patients was 19.5 minutes—six, 18, 21, and 60 minutes, respectively. This type of patient usually takes two to three hours to reach the hospital, according to the study authors.

There were also two false-positive alarms, one related to dysrhythmias and one due to a programming error. Both of these devices were successfully adjusted following the false alarm and had no more problems during the study follow-up.

With support from Angel Medical, the investigators have begun enrolling a phase 3 study that will include between 1000 and 3000 high-risk patients. All the patients in the study will be implanted with the monitor, but they will be randomized to the monitoring turned on or off. The study end points will include hard end points such as death and development of new Q waves, according to Gibson.

The device is currently intended only for high-risk patients such as those with previous ACS, diabetes, or renal insufficiency, but it may eventually be tested in a wider range of patients at risk for coronary disease. The researchers are also developing a version of the ST-segment monitoring algorithm for implantable defibrillators.