Methadone prolongs the QTc interval. Is the degree of QTC widening correlated to worse outcomes after overdose?
The authors of a new study concluded the triage QTc can predict death, intubation, and respiratory arrest. QTc thresholds of 470, 447.5, and 450 msec had sensitivity (95 % CI) and specificity (95 % CI) of 87.5 (47.3-99.7), 86.8 (74.7-94.5), and 77.3 (62.2-88.5), respectively.
My Thoughts
Respiratory depression is the predominant cause of death in methadone overdoses. QTc interval prolongation may have the potential to help predict outcomes, but the QTc thresholds in this study were really not that prolonged. Patients on chronic methadone without overdose have baseline QTc intervals longer than those in this study after overdose.
Application to Clinical Practice
Many factors contribute to the ultimate disposition of methadone overdose cases. Even if QTc widening is correlated to outcomes, it really won't change our management.
References
Farsi D, et al. The correlation between prolonged corrected QTc interval with the frequency of respiratory arrest, endotracheal intubation, and mortality in acute methadone overdose. Cardiovasc Toxicol 2014 May 9. [Epub ahead of print] [PMID 24811951]
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