Electrocardiography is a convenient bedside tool that can provide important diagnostic information in assessing patients after cyclic antidepressant (CA) overdose. Many researchers have been interested in predicting seizures, ventricular dysrhythmias, or death after CA overdose using electrocardiographic parameters, including the amplitude of the R wave and the R wave/S wave ratio in lead aVR. R-wave amplitude ≥3 mm and R wave/S wave ratio ≥0.7 were the most sensitive predictors of seizures or dysrhythmias in a series of patients who overdosed on CAs (sensitivity 81% and 75%, respectively). Also, it has been suggested that decreases in the amplitude of the R wave and R wave/S wave ratio in lead aVR may be related to the level of consciousness and be informative in predicting recovery from toxicity after CA overdose. With regard to the significance of lead aVR in the assessment of patients after CA overdose, it seems that the identification of the R and S waves in this lead is among the basic principles for all physicians and nurses involved in the care of patients with CA poisoning.
I have recently read the chapter on CAs by Liebelt in the most recent edition of Goldfrank’s Toxicologic Emergencies . Surprisingly, the author incorrectly illustrated the Q wave (instead of the S wave) in the description of the measurement of the R wave in lead aVR in significant CA poisoning (Figure 73-3, p. 1053). The correct S wave in lead aVR, from 1 of my patients with CA poisoning, is illustrated in Figure 1 . In this lead, the R wave is a terminal R wave, and downward deflection before that is essentially an S wave. Therefore, the S wave is measured in millimeters as the depth of the initial downward deflection.
