CHICAGO — Reporting on the annual meeting of the American Heart Association (AHA; Dallas) is a bit like attempting to understand an ocean by dipping a bucket of water out of it.
To help, AHA media people provide handouts that highlight, from the massive number of presentations and abstracts, what they feel is most media-worthy. But those highlights seldom focus on particular brands of medical devices or their manufacturers.
Thus, Cambridge Heart (Bedford, Massachusetts) scored a minor coup with the AHA’s release of a statement on results of the Alternans Before Cardioverter Defibrillator (ABCD) trial, demonstrating equivalence of the company’s Microvolt T-Wave Alternans (MTWA) Test — a computer drive, non-invasive test — with the traditional invasive and more expensive electrophysiology (EP) tests to predict a patients’ risk for sudden cardiovascular death (SCD). The news release was followed by a press conference presenting the results.
ABCD demonstrated the test’s ability to determine which patients with a history of ischemic heart disease and at high risk for SCD would actually benefit from an ICD, essentially a clinical guessing game.
That ability fills a poorly met need. Estimates are that only one in eight patients who needs an ICD actually has one implanted and many implanted with ICDs never receive shocks with them. One report at the AHA meeting estimated that in a cost-effective analysis, it takes 17 ICD implants to save one life.
David Rosenbaum, MD, director of the MetroHealth Heart and Vascular Center and professor of medicine at Case Western University (Cleveland) — lead author of the study and a Cambridge Heart consultant — noted that the standard EP study “has significant limitations,” including “a small risk and [requiring] a high degree of expertise.” Its invasiveness involves catheter electrodes placed into the heart and electrical impulses delivered to induce an abnormal heart rhythm.
By contrast, MTWA provides non-invasive measurement of small beat-to-beat fluctuations of what is called T-wave amplitude on an electrocardiogram (ECG). These tiny heartbeat variations are detected with Alternans Sensors while the heart rate is elevated by exercise, similar to a standard stress test, use of pharmacological agents or pacing. Cambridge Heart says that the association between T-Wave abnormalities and SCD risk has long been known but couldn’t be properly analyzed until the advent of advanced computer technology.
The AHA called the trial a first in terms of its diagnostic strategy.
ABCD followed 566 patients at 43 medical centers in the U.S., Germany and Israel, for an average of 1.9 years. All patients had previous heart damage from coronary artery disease but none had previously experienced a cardiac arrhythmia.
The participants underwent MTWA and EP tests with blinded adjudication, and they were then implanted with ICDs manufactured by St. Jude Medical (St. Paul, Minnesota) if either test was positive, and at the physician’s discretion if both tests were negative.
EPS and MTWA-directed strategies had comparable one-year positive (11% and 9%, respectively) and negative (96% and 95%, respectively) predictive values.
Event rates were higher at one year in patients with ICD therapy guided by both MTWA-directed and EPS alone strategies. The event rates for patients with both a negative MTWA test and EPS were 2%.
The overall rate of arrhythmic events was 7% after one year and 13% over two years. Thus, the study indicated that a strategy for screening patients for SCD risk which includes MTWA could improve the process of selecting patients who can benefit from ICD therapy.
Rosenbaum said utilizing both tests would be useful “because the tests measure different things: EP measures how electrical waves spread across the heart as it beats, and the MTWA measures how the heart cells recover from those electrical activities. We need to adopt the mindset for SCD screening that we currently have for breast cancer screening: screening of “appropriately selected patients at regular intervals.”
Another important finding was the unexpected time dependency of risk markers for SCD, Rosenbuam said. “We found that the EP study was not predictive until nine months or more and then remained predictive for two years, while the MTWA test was predictive as early as six months but was no longer predictive of outcomes by 12 months.”
Cambridge Heart recently reported that WellPoint/ Anthem has revised its coverage policy bulletin on Microvolt T Wave Alternans, agreeing to make it a covered benefit for its beneficiaries in California and 13 other states. The revised policy now says Microvolt T-wave Alternans using the spectral analytic method is considered medically necessary for the evaluation of patients at risk of sudden cardiac death who meet the approved criteria for implantable cardioverter defibrillator placement.
In an earlier-stage study focused on heart disease diagnostics:
Douwe Mulder of the University Medical Center Groningen (Groningen, the Netherlands), reported on the use of skin autofluoresence (AF) to predict adverse events after acute ST-elevation myocardial infarction (STEMI), or acute heart attack.
STEMI — a combination of sugars, proteins and lipids — associated with increased inflammation and oxidative stress, which in turn produces what are known as advanced glycation end products (AGEs), some of which fluoresce.
Skin AF was assessed in the lower arm of 88 STEMI patients within 72 hours of hospitalization and during a one-year follow-up, major adverse cardiac events occurred in 11 patients (four deaths, four heart attacks, three heart failure), and the researchers said the study demonstrated “that skin AF was an independent predictor of MACE.”