ASSESSMENT OF THE TERMINAL 40-MILLISECOND QRS VECTOR IN CHILDREN WITH A HISTORY OF TRICYCLIC ANTIDEPRESSANT INGESTION

Tricyclic antidepressant (TCA) ingestions remain a serious and not uncommon overdose in children. In adults, a terminal 40 millisecond QRS vector (T40-ms) between 120 and 270 degrees has been proposed as a marker for TCA overdose; however, the normal rightward deviation and high incidence of incomplete right bundle branch block noted in the electrocardiograms (ECGs) of young children may limit the usefulness of this criterion in this population. A retrospective chart review of pediatric patients less than 11 years of age admitted to the Hospital for Sick Children with birth dates after 1971 identified by International Classification of Diseases, Ninth Edition, coding for TCA ingestion was undertaken, and data related to complications were collected and reviewed. The ECGs of 35 children presenting with TCA ingestion were examined by two blinded cardiologists and the T40-ms as well as QRS, QTc, and PR intervals were calculated and compared to those of 35 healthy age-matched controls undergoing routine ECGs. In the 35 children (aged 48 +/- 39 months [mean +/- SD]) with a history of TCA ingestion, symptoms were categorized as significant in 18 (51%), mild in 12 (34%), and none in five (14%). Seizures were present in 13 (37%), hypotension in three (9%), and arrhythmias in five (14%). The mean T40-ms axes in the TCA and control groups were 111 +/- 66 degrees and 97 +/- 71 degrees, respectively. A T40-ms between 120 and 270 degrees had a sensitivity of 38% and a specificity of 74%. A marked variability in the T40-ms was noted in both the exposed and control groups, QRS duration, QTc interval, and PR interval did not differ significantly from controls, even when only patients with significant symptoms were compared. Given its extreme variability in normal control children, the T40-ms axis does not appear to be useful for predicting TCA ingestion in children.