Duration of QRS disturbances after severe tricyclic antidepressant intoxication

While the clinical toxicity of tricyclic antidepressants, particularly the development of seizures and arrhythmias, has been strongly correlated with a QRS interval of greater than or equal to 100 msec on electrocardiography, the resolution pattern of QRS abnormalities remains poorly defined. We prospectively monitored 22 consecutive patients who were referred to a regional poison center after a tricyclic antidepressant ingestion associated with a QRS interval of greater than 100 msec. An ECG was obtained every 6-8 h in all patients until the QRS interval was less than 100 msec. Among enrolled patients the mean maximal QRS interval was 145 msec. Ten patients (45.5%) developed seizures while 6 (27%) developed cardiac arrhythmias. The time from ingestion to the last ECG demonstrating a widened QRS interval was a median 12.3 h (range 1-70 h); the time from ingestion to the first ECG with a QRS less than 100 msec was a median 19.3 h (range 3-78 h). No patients developed seizures or life-threatening cardiac arrhythmias after the QRS interval was less than 100 msec. Ten patients received sodium bicarbonate while 12 did not. There were no significant differences in the duration of QRS widening between the two groups. These data suggest that the typical period of QRS prolongation after severe tricyclic antidepressant ingestion is 12-18 h but may be as long 3 d. The factors which determine the duration of QRS widening are unclear. Sodium bicarbonate may not reduce the total duration of QRS disturbances.