Electrocardiographic criteria for tricyclic antidepressant cardiotoxicity.

To determine if electrocardiographic findings characterize tricyclic antidepressant (TCA) overdose and cardiotoxicity, 25 patients suspected of taking an overdose of TCA were studied. Toxicologic assays for a TCA were positive in 11 patients (+TCA, n = 11). Toxicologic study results for a TCA were negative in 14 patients (-TCA, control subjects). Patients with positive TCA results (+TCA) had a significantly greater heart rate (117 +/- 23 vs 100 +/- 22 beats/min, p less than 0.05), QRS duration (103 +/- 15 vs 87 +/- 10 ms, p less than 0.005) and corrected QT interval (449 +/- 38 vs 418 +/- 36 ms, p less than 0.05) than control patients (-TCA) on admission. Patients with positive TCA results also had a more rightward terminal 40-ms frontal plane QRS vector (195 +/- 51 degrees vs 54 +/- 64 degrees, p less than 0.001) than control patients. This observation has not been previously reported. A terminal QRS vector of 130 degrees to 270 degrees accurately discriminated between -TCA and +TCA patients (positive and negative predictive value = 1.00). Counterclockwise rotation (normalization) of the terminal frontal plane QRS vector was noted in +TCA patients during hospitalization. All +TCA patients had a sinus tachycardia, a corrected QT interval 418 ms or longer, and a terminal QRS vector between 130 degrees and 270 degrees. Using these values as selection criteria, a computer-aided search of 15,064 electrocardiograms (ECGs) recorded in our emergency department was performed. The likelihood of encountering such an electrocardiographic pattern in this population was 1.0%.(ABSTRACT TRUNCATED AT 250 WORDS)