Heart rate turbulence and microvolt T-wave alternans in patients after myocardial infarction

Sulimov et al.,¹ in a study published online in the Journal on 31 July 2012, report on the predictive value of heart rate turbulence (HRT) and microvolt T-wave alternans (mTWA) measured in 24 h ambulatory electrocardiogram monitoring, for sudden cardiac death (SCD) in patients after myocardial infarction (MI). The work is important because it focuses on patients with preserved or moderately impaired left ventricular function (who are the ones dying from SCD at higher absolute numbers than the patients with a left ventricular ejection fraction [LVEF] ≤35%), and considers HRT, mTWA, and a host of other ‘more traditional’ SCD predictors. During follow-up of 12 months, the authors found that both mTWA and HRT onset absolute values were higher, and HRT absolute slope values were lower in non-survivors (who had suffered death in general or SCD) than in survivors. There are some limitations in this study, which should be considered before one attempts to extrapolate its findings and conclusions to the post-MI setting of patients with preserved or moderately impaired left ventricular function: (i) The study is reported as a ‘single centre, prospective observational’ in design, but there is no information whether this was a consecutive series of 111 patients, who agreed to be recruited, taking into consideration the reported exclusion criteria. (ii) The inclusion of patients with a previous MI which had occurred in the previous 2 months to 36 years is of concern when the follow-up was limited only to 1 year. One wonders what the results would be, had the authors' cohort consisted of a consecutive series of patients who underwent testing at a predetermined time point after their MI. Conclusions from such hypothetical study would have been confidently extrapolated to any practice setting. Although the authors aimed at studying patients with preserved or moderately impaired left ventricular function, the parameter of LVEF with the dichotomy of <40% and >40% ‘crept’ in the analyses and the discussion, attesting to the time-honoured importance of this predictive parameter of non-arrhythmic cardiovascular mortality and SCD. Perhaps, a lesson that could be drawn from this study is that we should be evaluating HRT and mTWA in post-MI patients irrespective of their LVEF (instead of limiting our observations to patients with ‘preserved or moderately impaired left ventricular function’), when the objective is to define the independent predictive value of these two SCD indices. However, a more suitable modus operandi (for both practice and research) that conforms with the current ‘real-world’ experience is to implement an implantable cardioverter-defibrillator (ICD) for all post-MI patients with an LVEF ≤35%, and reserve testing (perhaps annually) with HRT and mTWA (or other SCD predictors) for patients with a higher LVEF, in order to decide if and when such patients should receive their ICDs. Otherwise we should not hope to see light at the end of the tunnel soon; and this applies to both practice and research.

Conflict of interest: none declared.

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