Response to: “QT Interval Shortening After Bariatric Surgery—Mind the Heart Rate Correction Equation”

Abstract

Dear editor, With great interest, we read the response by Schultes and colleagues [1] to our recent systematic review assessing the changes in heart rhythm disorders after bariatric surgery [2]. We feel that Schultes et al. raise a very interesting but valid point. Indeed the changes in electrocardiogram (ECG)–related parameters, such as QT interval, are dependent on the used corrected formula. However, not directly the subject of our review, it opens the discussion that the existing heart rate correction formulas might not be suitable to assess QT interval–related changes after bariatric and metabolic surgery. As pointed out in the study by Grasser et al. [3], using Bazett’s formula might overestimate the change in QT interval after bariatric surgery. However, the problems related to the usage of formulas to correct QT interval for heart rate are not new. In a review done by Rabkin et al. [4], twenty-five different formulas were found in the literature, all of them based on a different patient population and none of them specifically validated for the use in patients with obesity. The formulas were either for correcting or predicting the QT interval [4]. The core problem here is the absence of a “gold standard” to identify the QT interval corrected for heart rate [4]. As pointed out in our systematic review [2] and in the review done by Rabkin et al. [4]. Bazett’s formula is frequently used and that has not changed in the last years, despite attempts to develop a “better suited alternative formula.” As pointed out by Schultes et al. [1] and Grasser et al. [3], Bazett’s formula “overcorrects” the measured QT interval at fast heart rates and possibly “under corrects” at low heart rates [4, 5]. It is a difficult task to assess the true “over” and “under” correction in absence of a gold standard. This is probably the reason why Bazett’s formula is still widely used, despite its critics [4–6]. Other formulas have also been criticized, such as the Fridericia formula [4]. This formula has been more precise than Bazett’s formula; however, the risk of bias at either extreme of heart rate(s) is also present. So, in conclusion, our search for newer QT correction and/or prediction formulas is not over.