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Tricyclic Antidepressants (TCA) - Lack of terminal 40msec R wave (R wave in AvR, S wave in I, AvL) means the patient is NOT TCA toxic. - 40msec R wave + QRS >100msec = possible TCA toxicity, treat with NaHCO3 and recheck ECG. - TCA toxicity defined by ECG; if QRS > 100msec, 33% seizures; if QRS > 160msec, 50% v tach Boehnert MT, Lovejoy FH Jr. Value of the QRS duration versus the serum drug level in predicting seizures and ventricular arrhythmias after an acute overdose of tricyclic antidepressants. N Engl J Med. 1985 Aug 22;313(8):474-9.