Discussing heart rate turbulence and microvolt T-wave alternans in patients after myocardial infarction: Response

We thank Dr Madias for his interest to our manuscript. In response to his question about our patient series, all consecutive patients who were admitted to our clinic due to chronic heart failure or coronary artery disease deterioration were included into the study. As for heterogeneity of the population regarding time elapsed from myocardial infarction (MI), we intentionally did not use the pre-specified time interval from the previous MI to the moment of inclusion in our study as an inclusion criterion, because we intended to analyse the possible influence of this variable on investigated parameters [microvolt T-wave alternans (mTWA) and heart rate turbulence (HRT)]. This analysis indicated that mTWA and HRT were independent of the time elapsed after MI and, therefore could be measured at any time without changing their value.

Nevertheless, Dr Madias's suggestion that testing should be performed at a predetermined time point after MI seems to be highly reasonable. However, the main point in this case would be the choice of the appropriate time interval after MI, especially for the patients with preserved left ventricular ejection fraction (LVEF). This task seems quite difficult, because clinical and pathophysiological criteria for total healing of MI differ a lot (28 days from the clinical point of view, according to the universal definition of MI, and from 6 to 8 weeks histologically). Nevertheless, this suggestion is very interesting, requires a different prospective study and may be part of our future research.

The value of LVEF for risk stratification for sudden cardiac death (SCD) should not be underestimated, and in our analysis we used it as the most important predictive independent factor. However, we also tried to use mTWA and HRT parameters as an additional risk factor in the subgroups of patients with reduced and preserved LVEF, and found that some results were different. For example, in the group with LVEF <40% both HRT and mTWA parameters at 05.00 AM showed no significant predictive value regarding SCD and cardiovascular mortality, whereas mTWA at heart rate 100/min ≥53 mcV retained its significance, and in the subgroup of patients with LVEF ≥40% increasing of mTWA value at 05.00 AM ≥18.5 mcV was associated with a 7.5-fold increase in overall mortality risk with no impact on SCD risk. However, these subgroups were small and the findings also require future large prospective studies.

We agree with Dr Madias that according to the existing guidelines¹ all post-MI patients, with an LVEF ≤35% should receive an implantable cardioverter-defibrillator (ICD) not earlier than 40 days after MI. The problem is much more difficult in post-MI patients with preserved or moderately impaired LVEF. It is possible that using HRT and TWA can influence the decision to implant ICD in this cohort of post-MI patients. We hope that in the real-world practice, where the number of ICD implantations is still limited, additional evaluation of HRT and mTWA in patients with preserved or moderately impaired LVEF will help to identify the time when ICD should be implanted.

Conflict of interest: V.S. did lecturing and research for Solvay Pharma, Sanofi, Nycomed, General Electric, Cordis a Johnson & Johnson; lectures for Boehringer Ingelheim, Bayer, Astra Zeneka. Elly Lilly; D.T. did lecturing and research for General Electric and Sanofi; E.O. received travel fees by General Electric and Sanofi.

Reference