Which test result would support a diagnosis of suspected TCA overdose?

• A. Prolonged QT interval on EKG
• B. Elevated TSH
• C. Hyperkalemia on basic metabolic panel
• D. Increased creatinine clearance

Answer: (A)

TCAs overdose disrupts cardiac conduction by blocking fast sodium channels in the heart, which slows depolarization and widens the QRS complex on the EKG. This conduction delay often translates into prolonged intervals on the tracing, including a prolonged QT interval, making it a supportive finding for suspected TCA toxicity. The other options don’t fit the typical toxic profile: an elevated TSH points to thyroid disease, hyperkalemia would show its own characteristic ECG changes due to electrolyte disturbance, and increased creatinine clearance isn’t a feature of TCA overdose. In this clinical picture, a prolonged QT on EKG is a meaningful clue that raises suspicion for TCA toxicity.