Wide QRS tachycardia in a young woman with a drug overdose.

A depressed young woman attempted suicide by taking approximately 2 g of nortriptyline. She had multiple seizures, a systolic blood pressure of 50 mm Hg, and a respiratory arrest and was comatose when brought by ambulance to the emergency department, where she was immediately intubated. The electrocardiogram recorded on admission shows a minimally irregular wide-QRS tachycardia with a long QT interval (heart rate, 104 beats/minute; QRS duration, 0.20 seconds; QTc interval, 0.52 seconds) that could be ventricular tachycardia but is probably sinus tachycardia with right bundle branch block and a northwest QRS axis (Figure 1). An electrocardiogram recorded 4.4 hours later shows a nearly identical heart rate (105 beats/minute), incomplete right bundle branch block (QRS duration, 0.115 seconds), a markedly rightward QRS axis, a long QTc interval (0.54 seconds), and a rhythm that is clearly sinus (Figure 2). In both electrocardiograms the terminal 0.04-second QRS vector in the frontal plane is in the northwest quadrant, i.e., between 180° and 270°. Tricyclic antidepressants are used far less frequently than they were 20 years ago, when it was estimated that they accounted for some 500,000 drug overdoses in the USA per year, with a mortality rate disproportionately higher than with other drug overdoses (1). From these cases emerged recognition of a typical electrocardiographic pattern of overdose with tricyclic antidepressants: sinus tachycardia, a corrected QT interval of 0.418 seconds or longer, and a terminal 0.04-second QRS vector in the frontal plane between 130° and 270° (2). These criteria had positive and negative predictive values for tricyclic ingestion of 66% and 100%, respectively, when tested on 299 patients with drug overdose, and the efficiency of the electrocardiogram as a diagnostic test was 97% (2). Both of our patient’s electrocardiograms met all three of these criteria. Wide QRS tachycardia in a young woman with a drug overdose