CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Anil K. Gehi, MD* and
J. Anthony Gomes, MD, FACC
* Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1030, New York, New York 10029 (Email: anil.gehi{at}msnyuhealth.org).
We appreciate the thoughtful comments of Dr. Chan and colleagues regarding our meta-analysis of microvolt T-wave alternans (MTWA) and wish to expand upon several points (1).
As dicussed by Dr. Chan and colleagues and as we pointed out in our Discussion section, very few studies have demonstrated whether MTWA is predictive of future arrhythmic events independent of other well-established clinical predictors. There is substantial evidence regarding the prognostic utility of other risk predictors, including ejection fraction (EF), signal-averaged electrocardiogram (ECG), heart rate variability, electrophysiologic study, and baroreflex sensitivity. Though MTWA may be the test currently in vogue, until MTWA is shown to add substantial prognostic value independent of other predictive tests, including EF, its clinical utility will not be clear.
Also, as pointed out by Dr. Chan and colleagues, future studies of MTWA should consider all cause and cardiac mortality in addition to arrhythmic events as primary end points. As stated in our Discussion section, this is a limitation of prior studies and likely due to their relatively small size, thus resulting in a lack of hard end points. As highlighted by the recently published Defibrillator in Acute Myocardial Infarction Trial (DINAMIT) (2), a decrease in arrhythmic mortality does not necessarily translate to a decrease in cardiac or overall mortality.
Additionally, it is important to emphasize an issue not raised by Dr. Chan and colleagues. That is, a strategy must be developed for proceeding when MTWA testing is non-diagnostic, which occurs on average in one-third of patients. Although a non-diagnostic test seems to carry the same prognosis as a positive test in previous studies, fundamentally it seems illogical to consider a non-diagnostic test to be relevant to the prediction of arrhythmic events. For example, events in these patients may have nothing to do with MTWA but to other factors such as heart failure.
Thus, future clinical studies of MTWA need to be carefully designed. Given the current guidelines for implantable cardioverter-defibrillator (ICD) implantation, it would be unethical to randomize patients with severe left ventricular (LV) dysfunction to ICD implantation, dependent on the results of MTWA testing. The most prudent approach may be the development of a sudden-death registry. Patients with structural heart disease, regardless of EF, could be enrolled in a registry after performing a variety of prognostic tests on them such as EF, signal-averaged ECG, and heart rate variability in addition to MTWA. By following these patients prospectively, clinicians could better understand how to incorporate MTWA as well as other established predictors into the decision for ICD implantation. In fact, we have proposed the development of a scoring system for risk stratification that incorporates all such variables to guide ICD implantation for primary prophylaxis (3). In addition, such an approach may help to utilize our health care resources more efficiently.
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References
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1. Gehi AK, Stein RH, Metz LD, Gomes JA. Microvolt T-wave alternans for the risk stratification of ventricular tachyarrhythmic eventsa meta-analysis. J Am Coll Cardiol 2005;46:75-82.[Abstract/Free Full Text]2. Hohnloser SH, Kuck KH, Dorian P, et al. Prophylactic use of an implantable cardioverter-defibrillator after acute myocardial infarction N Engl J Med 2004;351:2481-2488.[Abstract/Free Full Text] 3. Gehi A, Haas D, Fuster V. Primary prophylaxis with the implantable cardioverter-defibrillatorthe need for improved risk stratification. JAMA 2005;294:958-960.[Free Full Text]
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