LETTERS TO THE EDITOR
Microvolt T-Wave AlternansIs There Anything That Can Be Done to Save It?
John E. Madias, MD*
* Division of Cardiology, Elmhurst Hospital Center, 79-01 Broadway, Elmhurst, New York 11373 (Email: madiasj{at}nychhc.org).
The sobering results reported in the contribution of Chow et al. (1), published in the November 11, 2008, issue of the Journal, calls for a serious and in-depth reassessment of microvolt T-wave alternans (MTWA) technology for its role in the identification of patients with ischemic and nonischemic cardiomyopathy and who are most likely to benefit from implantable cardioverter-defibrillator (ICD) deployment. Previous observational studies have concluded that MTWA predicts arrhythmic events and therapeutic ICD shocks, in patient populations with diverse cardiac pathologies. In contrast, the prospective study under consideration (1)—which comprised 575 patients who met MADIT-II (Multicenter Automatic Defibrillator Implantation Trial II) criteria for an ICD implantation (post-myocardial infarction status and an ejection fraction of  30%), had an MTWA assessment before the ICD implantation, and were followed for at least 2 years—showed that the risk of suffering a ventricular arrhythmic event was no different between the patients with a negative MTWA test and those with a non-negative MTWA test, although the latter had higher total mortality. What is more disconcerting is that this study is published simultaneously with another, based on a subgroup of 490 patients from the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) cohort (2), which also concluded that MTWA testing did not predict arrhythmic events or mortality. After reading these reports, how does one act when facing a patient who might be a candidate for an ICD implantation? Should one go ahead with the ICD implantation or resort to testing for MTWA? Does MTWA still have some role to play? One approach is to wait and comfort ourselves with the routine pronouncements that more well-designed studies, enrolling larger number of "representative" patients and with longer follow-up periods, are in order. In reference to the latter, a long follow-up period has its disadvantages, because one should not expect a single, initially carried out MTWA test to be predictive of clinical outcomes of patients afflicted by a changing disease state over a protracted period of time, and thus periodic MTWA assessment (every 6 to 12 months?) might be advisable. Wouldn't this be prudent for other tests (e.g., exercise stress testing), and thus shouldn't this also apply to MTWA evaluation? This reader does not expect any "light in the tunnel" to be forthcoming by resorting to "more studies" with "larger study cohorts" and has put his hopes only in some "tinkering" with the implemented MTWA testing technology. Vast experience indicates that marked alterations of the morphology, amplitude, and polarity of the T waves and J-T intervals are commonplace in both normal subjects and patients. Some of these changes can be traced to alterations in heart rate, but most of them remain unexplained and are encountered in clinically stable individuals. One wonders as to the impact of such changes on the magnitude of MTWA. The magnitude of the MTWA (not reported in the study under consideration [1]) is of significance for both quantitative and qualitative study designs; after all, a cut point of  1.9 µV is implemented for the characterization of a test as positive/negative/indeterminate. It has been speculated (not shown) that the MTWA magnitude might be T-wave amplitude-dependent (3), and thus it might be of value to adjust the magnitude of the MTWA by the amplitude of the corresponding T waves used in the measurement/calculation of MTWA. Such a notion might be more applicable to the time-domain MTWA methodology using a modified moving average analysis, but it applies in principle to the spectral analytic method. In the latter, one should expect that this "indexing" of MTWA magnitude values should consider the entire J-T interval in some form of representation. However, one should attempt to take the first step (however crude) of "indexing" the MTWA magnitude values by the corresponding T-wave amplitudes. This should be applied separately for patients with normal and prolonged QRS complexes. In this context, it might be of value to the readership for Chow et al. to supply us with the quantitative results of the MTWA of their study and evaluate whether adjusting such MTWA values by the corresponding T-wave amplitudes leads to an MTWA index with worse, the same, or better prognostic power than they have identified in their study.
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1. Chow T, Kereiakes DJ, Onufer J, et al. MASTER Trial Investigators Does microvolt T-wave alternans testing predict ventricular tachyarrhythmias in patients with ischemic cardiomyopathy and prophylactic defibrillators? The MASTER (Microvolt T Wave Alternans Testing for Risk Stratification of Post-Myocardial Infarction Patients) trial J Am Coll Cardiol 2008;52:1607-1615.[Abstract/Free Full Text]2. Gold MR, Ip JH, Costantini O, et al. Role of microvolt T-wave alternans in assessment of arrhythmia vulnerability among patients with heart failure and systolic dysfunction: primary results from the T-Wave Alternans Sudden Cardiac Death in Heart Failure Trial Substudy Circulation 2008;118:2022-2028.[Abstract/Free Full Text] 3. Madias JE. The need for studies to evaluate the reproducibility of the T-wave alternans (TWA), and the rationale for a correction index of the TWA Indian Pacing Electrophysiol J 2007;7:176-183.[Medline]
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J. Am. Coll. Cardiol. 2009 53: 1246-1247.
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