T-wave alternans during exercise testing calculated by the method of 'modified moving average'

I enjoyed reading the contribution by Nieminen et al.1 focusing on the predictive role for cardiovascular mortality, especially sudden cardiac death, of the T-wave alternans (TWA) calculated by the analytical method of modified moving average in patients undergoing clinically indicated exercise testing; the studied patients were not suffering from congestive heart failure, and did not have a low left ventricular ejection fraction, enabling the authors to propose that TWA assessment may be of predictive use for a wider pathophysiologic range of patients with cardiovascular disease, than considered heretofore.2 The authors analysed and reported the maximum TWA at heart rates <125 beats min−1. Since the bulk of the work on TWA has implemented the spectral method of analysis,2,3 which uses TWA values calculated at peak heart rates ≤110 beats min−1, it would be very contributory by the authors to report such information from their cohort. Indeed, this will be of importance in the current climate of interest in comparisons of the spectral and time-domain analyses, reflected in the literature.4 It has been recently theorized that the magnitude of the TWA may be T-wave amplitude dependent,5,6 and thus changes in the T-wave amplitude in the course of exercise testing (a frequent encounter in the exercise laboratory) might impact the calculated TWA magnitude. Accordingly, as the T-waves change in amplitude (either decrease or increase) to a different degree in the different stages of the exercise testing, an alteration of the magnitude of the calculated TWA might occur, unrelated to electrophysiologically mediated degrees of arrhythmic or sudden cardiac death risk. This hypothesis can be evaluated by considering a TWA index, which takes into account the corresponding T-wave amplitude.7 The authors have a marvellous opportunity to evaluate the merit of such a TWA index, by analysing their data of the reported TWA values, adjusted by the corresponding amplitude of T-wave(s).