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 cells 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 (RaVR), the R-wave/S-wave ratio in lead aVR (R/SaVR), and the maximal limb-lead QRS interval were measured on the initial ECG.

RESULTS

RaVR 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/SaVR (1.4 versus .5, P < .001). The sensitivity of an RaVR of 3 mm or more was 81% and that of an R/SaVR of .7 or more was 75%, compared with 82% for QRS intervals greater than 100 milliseconds. The positive predictive value (PPV) of an RaVR of 3 mm or more was 43% and that of the R/SaVR 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 RaVR 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

RaVR and R/SaVR were greater in patients in whom seizures or arrhythmias developed after an acute TCA overdose. RaVR of 3 mm or more was the only ECG variable that significantly predicted these adverse outcomes.