• Davood Farsi, Amirhossein Mirafzal, Hossein Hassanian-Moghaddam, Zahra Azizi, Nyoosha Jamshidnejad, and Shahriar Zehtabchi.
• Department of Emergency Medicine, Iran University of Medical Sciences, Tehran, Iran.
• Cardiovasc. Toxicol. 2014 Dec 1;14(4):358-67.

AbstractCorrected QT interval (QTc) prolongation is long considered as a predisposing factor for the occurrence of torsade de pointes (TdP) and sudden cardiac arrest in methadone maintenance treatment. We aimed to elucidate the correlation between QTc prolongation and in-hospital death, respiratory arrest, and endotracheal intubation in acute methadone-intoxicated patients presenting to the emergency department and to assess the value of QTc in predicting these outcomes. A prospective cross-sectional study with a convenience sample of patients with acute methadone overdose was done. Participants were 152 patients aged 15-65 with negative urinary dipstick test for cyclic antidepressants, no history of other QTc-prolonging conditions and co-ingestions, no severe comorbidities affecting the outcomes, and positive urinary dipstick results for methadone. QTc intervals were measured and calculated in triage-time electrocardiogram (ECG). Death was correlated with QTc (P = 0.014) and length of ICU admission (P < 0.001). In multivariable analysis, death was independently associated only with length of ICU admission [odds ratio (OR) 95 % confidence intervals (95 % CI) 1.36 (1.14-1.61)]. Intubation and respiratory arrest were independently associated with QTc interval [OR (95 % CI) 1.03 (1.02-1.04) and 1.02 (1.01-1.03), respectively]. The receiver operating characteristics curves drawn to show the ability of QTc to predict death, intubation, and respiratory arrest showed thresholds of 470, 447.5, and 450 ms with 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. Our study showed that QTc is a potential predictor for adverse outcomes related to acute methadone intoxication. The correlations shown in this study between triage-time QTc and in-hospital respiratory arrest or intubation in methadone overdose may be of clinical value, whether these outcomes are hypothesized to be a reflection of background TdP or intoxication severity.

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