European Heart Journal Advance Access originally published online on October 13, 2007
European Heart Journal 2007 28(21):2691-2692; doi:10.1093/eurheartj/ehm395
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T-wave alternans during exercise testing calculated by the method of ‘modified moving average’: reply
Department of Pharmacological Sciences
Medical School FI-33014 University of Tampere,
Finland
Laboratory of Atherosclerosis Genetics,
Department of Clinical Chemistry,
Tampere University Hospital, Finland;
Medical School, University of Tampere, Finland
Ragnar Granit Institute, Tampere University of Technology,
Finland
Department of Clinical Physiology,
Tampere University Hospital;
Medical School, University of Tampere,
Finland
Tampere Polytechnic – University of Applied Sciences,
Finland
Heart Centre, Department of Cardiology,
Tampere University Hospital,
Finland
Department of Clinical Physiology, Z
Tampere University Hospital;
Medical School, University of Tampere, Finland
Heart Centre, Department of Cardiology,
Tampere University Hospital,
Finland
Department of Clinical Physiology,
Tampere University Hospital;
Medical School, University of Tampere, Finland
GE Healthcare Information Technologies,
Freiburg, Germany
School of Public Health,
University of Tampere,
Finland
Harvard Medical School, Cardiovascular Institute,
Beth Israel Deaconess Medical Center;
Boston, MA, USA
Department of Medicine,
University of Oulu,
Finland
Department of Clinical Physiology,
Tampere University Hospital;
Medical School, University of Tampere, Finland
Tel: +358 50 910 5150; Fax: +358 3 215 6170 E-mail: tuomo.nieminen{at}iki.fi
We appreciate Dr Madias' complimentary remarks about our study and his thoughtful suggestions regarding T-wave alternans (TWA) testing in sudden cardiac death risk stratification. Given recent interest in the modified moving average (MMA) and spectral method (SM), the question was raised regarding the predictability in our study using a target heart rate of 110 beats/min as in the SM studies rather than our criterion of maximum TWA at heart rates <125 beats/min. Although not reported in the current study,1 we found that the relative risks and negative predictive value of TWA at the reference heart rate of 110 beats/min were statistically significant and highly comparable to our results1 and those reported in papers based on SM.2
Dr Madias also raises the issue of whether TWA may be dependent on T-wave amplitude and suggests the use of a ‘TWA index’ to adjust for this factor. This is an interesting consideration and one that could potentially impact on the calculation of TWA with either MMA or SM. T-wave size is influenced by many factors, including heart rate, catecholamines, body size (particularly obesity), physical conditioning, and others. Catecholamines do increase T-wave amplitude; they have been associated with elevated TWA3 and are highly arrhythmogenic. However, the attendant increase in heart rate, as shown in pacing studies, decreases T-wave size while elevating TWA and risk for tachyarrhythmias. Owing to the complex interplay between elevated heart rate and catecholamines and other factors during the course of an exercise test, T-wave amplitude waxes and wanes, and TWA could be difficult to standardize as an index.
Notwithstanding these considerations, Dr Madias offers an interesting thought piece regarding the use of more complex formulae for calculating TWA potentially to improve its predictive performance. In the future, it will be worthwhile to assess whether changes in T-wave amplitude are directly linked to TWA or if they are an inconstant ‘fellow traveler’.
References
- Nieminen T, Lehtimaki T, Viik J, Lehtinen R, Nikus K, Koobi T, Niemela K, Turjanmaa V, Kaiser W, Huhtala H, Verrier RL, Huikuri H, Kahonen M. T-wave alternans predicts mortality in a population undergoing a clinically indicated exercise test. Eur Heart J (2007) [Epub ahead of Print].
- Gehi AK, Stein RH, Metz LD, Gomes JA. Microvolt T-wave alternans for the risk stratification fof ventricular tachyarrhythmic events: a meta-analysis. J Am Coll Cardiol (2005) 46:75–82.
[Abstract/Free Full Text] - Kop WJ, Krantz DS, Nearing BD, Gottdiener JS, Quigley JF, O'Callahan M, DelNegro AA, Friehling TD, Karasik P, Suchday S, Levine J, Verrier RL. Effects of acute mental stress and exercise on T-wave alternans in patients with implantable cardioverter defibrillators and controls. Circulation (2004) 109:1864–1869.
[Abstract/Free Full Text]
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