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Microvolt TWA test may have post-MI risk-stratification value even when
LV function is normal
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December 14, 2006 |
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Tokyo,
Japan - The microvolt T-wave-alternans (TWA) test, an
established option for stratifying sudden-death risk in post-MI patients with a
low LVEF, may also work in such patients with preserved systolic function,
according to an observational study appearing in the December 5, 2006 issue of
the Journal of the American College of Cardiology [1].
The authors, Dr
Takanori Ikeda (Kyorin University, Tokyo, Japan) and associates, found that
a positive TWA test was independently associated with a 20-fold increase in the
relative risk (p<0.0001) for "serious arrhythmic events" in a
prospectively enrolled cohort of 1041 acute-MI survivors with an LVEF >40%
treated at eight centers in Japan. It also emerged as the most significant of a
range of arrhythmic-risk predictors, including nonsustained VT and presence of
late potentials.
The arrhythmia end
point, assessed after an average of 32 months, encompassed confirmed instances
of "sudden cardiac death, cardiac arrest, or resuscitated ventricular
fibrillation" but excluded hemodynamically stable sustained ventricular
arrhythmias. Virtually all patients had undergone either PCI or bypass surgery
as their acute-MI reperfusion therapy.
Hazard ratios for serious arrhythmic events in post-MI patients with preserved LVEF, multivariate analysis
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Parameters that did not emerge as independently
significant: Presence of ventricular late potentials, LVEF >40% but
<45%, age >70, male sex, anterior-wall MI location, PCI, CABG,
antiarrhythmic drug therapy, beta-blocker therapy
As previously covered
by heartwire, abundant evidence suggests that the TWA test
marketed by Cambridge Heart (Bedford, MA), which uses a proprietary algorithm
for identifying the electrocardiographic T-wave abnormality, can help identify
post-MI patients with poor LV systolic function who are most likely to need the
protection of an implantable cardioverter-defibrillator. In this comparatively
high-risk population, a positive test supports a decision to implant a device. Their study, Ikeda et
al write, "is the first to show the prognostic value of microvolt TWA
compared with various other known risk variables in patients with preserved LV
function after acute MI." It further suggests that "microvolt TWA
could be used in the primary screening of patients for sudden cardiac death in
this patient population, because both the sensitivity and negative predictive
value of microvolt TWA were high (81% and 99.6%, respectively)." They
propose, however, that the test be a supplement to other sudden-death risk
assessments in this population because its positive predictive value was low,
at 9%. Quirks in the
management of many of the Japanese study's patients complicate its
interpretation, according to Dr Thomas Klingenheben (JW Goethe
University, Frankfurt, Germany) [2]. In
an accompanying editorial, he observes that 7% of the group had received
potentially proarrhythmic class I antiarrhythmic drugs during the follow-up
period and only 21% of the patients were on beta blockers. "Because beta
blockers are a mainstay of post-MI therapy in the US and Europe, with a highly
beneficial impact on prognosis, both the incidence of serious arrhythmic events
and the predictive power of [microvolt TWA] may be different in other MI
populations."