Demographic and Electrocardiographic Factors Associated With Severe Tricyclic Antidepressant Toxicity

Abstract

This study was designed to evaluate a historic cohort of pure tricyclic antidepressant overdose patients for factors associated with severe toxicity. Hospitalized tricyclic antidepressant overdose patients were identified by computerized discharge diagnosis (ICD-9 codes). Patients with a serum drug screen positive for tricyclic antidepressants and an emergency department 12-lead electrocardiogram were included in the study. Multiple drug overdoses were excluded. Patients were divided into two groups: minor toxicity (n = 41) and major toxicity (n = 65). Criteria for inclusion in the major toxicity group were the occurrence of seizures, endotracheal intubation, coma, arrhythmias requiring treatment, hypotension, or death. The following were found to be associated with increased likelihood of major toxicity (p < 0.05): ingestion of amitriptyline (odds ratio (OR) 2.57), age ≥ 30 years (OR 2.56), heart rate ≥ 120 bpm (OR 2.86), serum tricyclic antidepressant level ≥ 800 ng/mL (OR 5.20), terminal 40 ms QRS axis (T40-ms axis) ≥ 135 degrees (OR 2.73), QRS interval ≥ 100 ms (OR 2.74), QRS axis > 90 degrees (OR 3.68), and QTc interval > 480 ms (OR 3.89). The mean T40-ms axis on the initial ECG was more rightward in the major toxicity group (174 ± 84 vs 125 ± 91 degrees, p = 0.006).

We conclude that patients with severe tricyclic antidepressant toxicity tended to have a more rightward T40-ms axis than those with minor toxicity and that the presence of the above parameters was associated with an increased likelihood of severe toxicity.

KEY WORDS:

• antidepressive agents
• electrocardiography
• poisoning
• human