In this episode, I’ll discuss delayed QTc prolongation in overdose patients.
Patients who present to the ED with acute drug overdose and a QTc above 500 msec are known to have an increased risk of adverse cardiac event and are therefore proactively monitored for this development.
However some patients with drug overdose and an initial QTc below 500 msec will go on to have delayed prolongation of the QTc above 500 msec over hours or days from initial presentation. These patients are also at risk of adverse cardiac events due to the delayed presentation they may not be monitored as closely leading to a further delay in recognition and treatment of the problem.
While long acting cardiotoxic medications like citalopram and methadone are reported to be associated with delayed prolongation of the QTc, a group of authors performed a secondary analysis of a prospective cohort of ED toxicological patients in an attempt to identify risk factors for patients who initially have a normal QTc but later develop a prolonged QTc and risk of adverse cardiac event.
Over 1500 adult ED patients with acute drug overdose and initial QTc below 500 msec were analyzed. The group that had delayed QTc prolongation did indeed have a higher risk of adverse cardiac event and this risk remained statistically significant after adjustment for age, sex, race/ethnicity, number of exposures, serum potassium, and opioid exposure.
The authors also identified 2 risk factors that were associated with delayed QTc prolongation: Age over 45 years and multidrug overdose with 3 or more ingestants. The mean time to delayed QTc prolongation was about 40 hours.
This information can be used by ED clinicians to identify a cohort of patients that is at risk for delayed QTc prolongation and subsequent adverse cardiac event.
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