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Zachary Holmes, Dustin Orvin, John Carr, Determining QTc in acute care settings: What we (don’t) know, American Journal of Health-System Pharmacy, Volume 81, Issue 22, 15 November 2024, Pages 1187–1193, https://doi.org/10.1093/ajhp/zxae168
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How do you calculate a corrected QT interval (QTc)? What method is used by automated electrocardiogram (EKG) machines at your institution? Which formula should you select from an online resource? And which formula is used by drug sponsors during safety studies? Pharmacists have a critical role assessing medication risks in all practice settings,1-3 yet asking these questions regarding the risks related to QTc will yield inconsistent responses, at best. Several authors have described the pharmacist’s role in QTc interpretation, identified limitations of overemphasizing QTc alone when determining the risk of torsades de pointes (TdP), and proposed standards for pharmacists and other healthcare providers assessing the risk of QTc prolongation based on our current understanding,4,5 but these well-constructed houses are built on sand. Proper application cannot be posited while the undergirding assumptions remain inadequate.
QTc prolongation is a poorly understood risk factor that is often overemphasized in clinical practice. As a result, TdP has quickly become a boogeyman for new practitioners, while many seasoned pharmacists are exhausted of beating the proverbial dead horse. In the instance of QT-prolonging medications, therapy decisions should hinge on several factors, only one of which is the QTc. Making informed decisions requires data that is neither transparently published in the available literature nor consistently made available by the US Food and Drug Administration (FDA) in product packaging. Admittedly, data on drug-induced TdP is somewhat elusive given the disorder’s low incidence. Authors reporting on a health system in Belgium reported an incidence of 0.16% per year in hospitalized patients over a time period of 3 years—19 cases out of a total of approximately 119,000 admitted patients during that time period.6 Such numbers are difficult to replicate in clinical trials, thus limiting our ability to identify the true risk of TdP associated with individual medications. Clinicians vary significantly when interpreting QTc and, thus, estimating the risk of TdP. Among pharmacists, this may be traced as far back as doctor of pharmacy curricula, which have no standardized curricula for EKG/QTc interpretation. Noel et al7 summarized this best: “A pharmacist lacking the basic understanding of drug-induced QT prolongation and risk factors for torsades de pointes will either burden local providers with unnecessary calls, or worse, ignore a warning that could result in patient harm.” While the absence of standardized training and education is certainly a significant factor, one would be hard-pressed to develop such standards given the limited outcomes data available to clinicians.
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