Which ECG change is MOST likely observed in a patient with tricyclic antidepressant toxicity?

In cases of tricyclic antidepressant (TCA) toxicity, the most characteristic ECG finding is the presence of a terminal R wave in lead aVR. This specific change reflects the toxic effects of TCAs on cardiac conduction and is indicative of a broadening of the QRS complex, primarily through sodium channel blockade. The terminal R wave in aVR occurs as the depolarization pattern of the heart is altered, highlighting the importance of this finding in recognizing TCA toxicity.

The terminal R wave in aVR is significant because it suggests an underlying serious condition like arrhythmias or the increased risk of cardiac arrest associated with significant TCA overdose. Recognizing this change is crucial for timely intervention, as it may be a precursor to more severe manifestations such as ventricular dysrhythmias.

Other ECG findings associated with TCA toxicity, such as a widened QRS complex, are commonly documented. However, the terminal R wave in aVR stands out as a definitive marker that points specifically to the influence of tricyclics on cardiac electrical activity.