Final answer:
Cardiotoxicity is the most common cause of death from TCA poisoning.
Step-by-step explanation:
The most common cause of death from TCA (tricyclic antidepressant) poisoning is cardiotoxicity. TCA overdose can lead to life-threatening cardiac arrhythmias, such as ventricular tachycardia or ventricular fibrillation, which can result in death. The exact mechanism of cardiotoxicity is complex, but it involves blocking certain ion channels in the heart, leading to abnormal electrical activity.