Critical remark on the “heart rate differential method"/"HR‐diff" parameter

Abstract

We read with much interest the recently published article by Jeppesen and colleagues on seizure detection based on heart rate variability. 1 We are concerned because it presents an algebraic quandary in its basic formula, which challenges the interpretations of the results of the "HR-diff" parameter. This quandary was also present in an earlier publication from this group 2 but was not previously challenged.The authors claim to average or sum up the so-called "heart rate differential method" over 50 or 100 (in the formula k) R-R intervals using the following equation:As a result of the subtraction of two R-R intervals in each summand of the formula, all R-R intervals except the first two and last two will disappear mathematically, whatever value they may have:Taking into account that x k ≡ t k − t k+1 , where t k is the time of the k-th heartbeat, we come to the simple derivation:Following the shown simplification, this procedure results in only the total R-R interval change over the given number of about k (50 or 100) heartbeats. This, therefore, does not represent the heart rate variability, as it only shows the cumulative effect over time. This will lead to a different interpretation of the results as an "average" or "smoothing" of many intervals does not occur using this formula (except for the trivial averaging of two successive R-R intervals). As could then be expected, this parameter scores badly (visible in Figure 2 in 1 ) while this parameter scores better after prefiltering, which enables the possibility to place information from more than the four remaining arbitrarily chosen R-R intervals (-1;0;k;k+1) into the parameter. Therefore, the parameter "HR-diff" does not allow relevant smoothing or averaging on its own and only prefiltering enables some averaging/smoothing. Thus this parameter should be simplified as shown above to save some computational power, and the sum-formula should no longer be used as it stands. CONFLICT OF INTERESTNeither of the authors has any conflict of interest to disclose. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.