SERIAL ELECTROCARDIOGRAM CHANGES IN ACUTE TRICYCLIC ANTIDEPRESSANT OVERDOSES

Objectives: To describe the changes over time of the QRS interval and terminal 40-msec QRS frontal axis (T40-ms) in patients with acute tric yclic antidepressant poisoning, to identify clinical factors and treat ment associated with these changes, and to determine if patients with tricyclic antidepressant-related complications (seizures and/or arrhyt hmias) had differences in such serial electrocardiogram (EGG) changes when compared with patients without complications. Design: Prospective , observational, cohort study. Setting: Emergency departments of commu nity and university-based hospitals in Massachusetts that consulted a large regional poison center. Patients: Thirty-six patients who presen ted with an acute ingestion (<24 hrs) of a tricyclic antidepressant, w ho had at least three electrocardiograms in the first 8 hrs and serial ECGs until discharge, and who had a peak tricyclic antidepressant con centration of >300 ng/mL. Interventions: None. Measurements and Main R esults: The maximal limb-lead QRS interval and T40-ms axis were measur ed manually in all ECGs, The maximum recorded QRS interval occurred at the time of presentation for 24 (80%) of 30 patients whose QRS was gr eater than or equal to 100 msecs and a median time of 3 hrs (range 1 t o 9) for the other six patients, The maximum recorded T40-ms axis occu rred at the time of presentation for 31 (86%) of 36 patients and at a median time of 3 hrs (range 1 to 5) for the remaining five patients, T he minimum QRS interval observed remained greater than or equal to 100 msecs in 15 patients (range 100 to 140 msecs) and decreased to (100 m secs in 15 patients, The median time from presentation to the first EC G with a QRS<100 msecs was 20 hrs (range 1 to 153) in those 15 patient s, There were no significant differences in clinical characteristics a nd treatment (including sodium bicarbonate therapy) between the two gr oups, The minimum recorded T40-ms remained greater than or equal to 12 0 degrees in 30 patients and decreased to <120 degrees in six patients , The median time from presentation until the first ECG with a T40-ms axis <120 degrees was 13 hrs (range 2 to 30) for the six patients, All ECG measurements were greater and remained abnormal for a significant ly longer duration in those patients who developed seizures and/or ven tricular arrhythmias. These two ECG parameters demonstrated ongoing ch anges and persistent abnormalities despite clinical improvement in all patients except one. Conclusions: The conduction abnormalities seen i n severe tricyclic antidepressant toxicity vary widely in the time obs erved for resolution of these abnormalities and sometimes remain persi stently abnormal, Ail ECG parameters were significantly more abnormal in those patients who developed seizures and/or arrhythmias, Clinical improvement occurred both before and during these ECG changes.