Letter by Madias Regarding Article, “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”
To the Editor:
The disturbing news conveyed to clinicians in the article by Gold et al published in Circulation,1 requires a hard look at the microvolt T-wave alternant (MTWA) technology and its performance in stratifying patients with cardiomyopathy into those who may and may not need an implantable cardioverter-defibrillator. This prospective study of 490 patients from the Sudden Cardiac Death in Heart Failure Trial cohort has not confirmed the favorable predictive role for MTWA for arrhythmic events and therapeutic implantable cardioverter-defibrillator shocks,1 shown in previous observational studies. The authors should entertain the following questions: Is it realistic to expect a single MTWA test to predict outcome in patients with a changing disease state? Accordingly, it may be useful for the authors to analyze outcomes at 6, 12, and 18 months. If performance of MTWA testing in such an analysis is better than the one reported at the end of the follow-up period, perhaps periodic assessment of MTWA is in order. MTWA data were reported using the usual dichotomy of “positive” and “negative” (and “indeterminate”) based on the cut point of ≥1.9 μV. Is magnitude of MTWA of any value? Could quantitative reporting have a role, particularly when MTWA testing is repeated in the same patient(s)? T-waves (or J-T intervals) are notorious for their volatility in patients and normal subjects at rest (electrocardiography Holter recordings), during exercise testing, and in serial electrocardiography in the hospital and clinic, most often without an explanation because the patients are clinically stable. One wonders about the impact of such T-wave (or J-T interval) perturbations on the magnitude of MTWA irrespective of the status of vulnerability to ventricular arrhythmias. It has been theorized that the magnitude of MTWA may be T-wave (or J-T interval) dependent2 and that adjustment of the measured values of MTWA to the voltage of the T-wave (or J-T interval) might be of value. A first step in exploring this notion could be to divide MTWA values in μV by the amplitude of the corresponding (ie, used for the MTWA measurement) T-waves in mV and evaluate whether this “indexing” has improved the predictive power of MTWA. While we engage in more investigative work on MTWA (to be reported in the future) using the current format of MTWA technology, it may be advisable to go back and reanalyze data of already reported studies along the previous 2 lines of inquiry. First, it may not cost much or anything, and second, we may be met with pleasant surprises.
Gold MR, Ip JH, Costantini O, Poole JE, McNulty S, Mark DB, Lee KL, Bardy GH. 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.