ECG Review

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Clinical Scenario: The ECG shown in the figure was obtained from a previously healthy young adult admitted to the hospital intensive care unit for TCA (tricyclic antidepressant) overdose. In view of this history, is her initial ECG worrisome? If so, why?

Interpretation: There are several signs present on this patient’s initial ECG that are consistent with TCA overdose. These include sinus tachycardia, a relatively vertical (almost rightward) mean QRS axis, non-specific ST-T wave changes, incomplete right bundle branch block (RBBB), and QRS widening. It is of interest that P waves are not well seen in standard lead II. Instead, the diagnosis of sinus tachycardia has to be presumed from inspection of lead V₁ (that shows definite P wave activity). This was confirmed on subsequent tracings.

Although QT interval prolongation is probably the most commonly cited ECG sign of TCA overdose, it is not as good of a predictor of potentially lethal complications (from either seizures or arrhythmias) as QRS prolongation (to > 0.10 second). Determination of whether or not the QT interval is prolonged is difficult when the heart rate is rapid and the end of the T wave is indistinct (as in this tracing). Regardless, the presence of this degree of sinus tachycardia in a previously healthy young adult with a QRS interval that exceeds 0.10 second should clearly be cause for concern.

Suggested Reading

1. Goldberg RJ, et al. Cardiac complications following tricyclic antidepressant overdose. JAMA 1985;254:1772.