## Distinguishing Feature: Cardiac and Anticholinergic Toxicity ### TCA-Specific Adverse Effects **Key Point:** TCAs have a narrow therapeutic window and cause dose-dependent cardiac conduction abnormalities (QT prolongation, arrhythmias) and anticholinergic effects (dry mouth, urinary retention, constipation, tachycardia) — features largely absent in SSRIs. ### Mechanism Basis TCAs block: - **Cardiac sodium channels** (Class I antiarrhythmic-like effect) → QRS widening, bundle branch block, ventricular arrhythmias - **Muscarinic acetylcholine receptors** → anticholinergic syndrome - **Alpha-1 adrenergic receptors** → orthostatic hypotension SSRIs have minimal affinity for these targets and are cardiac-safe at therapeutic doses. ### Clinical Pearl **High-Yield:** TCA overdose is life-threatening (seizures, arrhythmias, coma); SSRI overdose is rarely fatal. This is the **single most important discriminator** in clinical practice and exams. ### Comparison Table | Feature | TCAs | SSRIs | | --- | --- | --- | | Sodium channel blockade | Yes (dose-dependent) | No | | Anticholinergic effects | Prominent | Minimal | | Cardiac conduction risk | High (QT↑, arrhythmias) | Low | | Orthostatic hypotension | Common | Rare | | Lethal in overdose | Yes | No | | Therapeutic window | Narrow | Wide | [cite:KD Tripathi 8e Ch 12]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.