ECG LEAD AVR VERSUS QRS INTERVAL IN PREDICTING SEIZURES AND ARRHYTHMIAS IN ACUTE TRICYCLIC ANTIDEPRESSANT TOXICITY

Study objective: To compare the value of ECG measurements from lead aVR with the QRS-interval duration in predicting seizures and ventricular arrhythmias due to acute tricyclic antidepressant (TCA) toxicity. Design: Prospective cohort series of referral calls from hospitals to a regional poison control center. Participants: Seventy-nine patients (mean age, 30+/-15 years) who presented within 24 hours of ingestion. Seizures occurred in 16 patients (20%) and ventricular arrhythmias in 5 (6%). Interventions: The amplitude of the terminal R wave in lead aVR (R(aVR)), the R-wave/S-wave ratio in lead aVR (R/S-aVR), and the maximal limb-lead QRS interval were measured on the initial ECG. Results: R(aVR) was greater in those patients who had seizures or arrhythmias than in those who did not (4.4 versus 1.8 mm, P<.001), as was R/S-aVR (1.4 versus .5, P<.001). The sensitivity of an R(aVR) of 3 mm or more was 81% and that of an R/S-aVR of .7 or more was 75%, compared with 82% for QRS intervals greater than 100 milliseconds. The positive predictive value (PPV) of an R(aVR) of 3 mm or more was 43% and that of the R/S-aVR of .7 or more 46%, compared with a PPV for QRS interval of 100 milliseconds or more of 35%. Multiple logistic-regression analysis demonstrated that an R(aVR) of 3 mm or more was the only ECG variable that significantly predicted seizures and arrhythmias (OR, 6.9 [95% CI, 1.2 to 40], P=.03). Conclusion: R(aVR) and R/S-aVR were greater in patients in whom seizures OF arrhythmias developed after an acute TCA overdose. R(aVR) of 3 mm or more was the only ECG variable that significantly predicted these adverse outcomes.