Referred pain from the heart is perceived in the left arm and the T1–T4 dermatomes because of:
- A Direct communication between vagal afferents and somatic sensory cortex
- B Antidromic activation of somatic C-fibers in the brachial plexus by cardiac sympathetic efferents
- C Convergence of visceral afferents from the heart and somatic afferents from the arm on the same second-order neurons in the dorsal horn at T1–T4 ✓
- D Release of substance P from cardiac afferents that diffuses to somatic nociceptors in the arm
Correct answer: C. Convergence of visceral afferents from the heart and somatic afferents from the arm on the same second-order neurons in the dorsal horn at T1–T4
Explanation
Referred pain is explained by the convergence-projection theory: visceral afferents from the heart (traveling with sympathetic T1–T4 fibers) and somatic afferents from the medial arm/chest wall synapse on the same second-order neurons in the dorsal horn at T1–T4. The brain misinterprets the source of pain as somatic because somatic input is far more frequent than visceral input, leading to mislocalization to the arm, chest, and jaw. This is why cardiac ischemia classically radiates to the left arm and jaw in the T1–T4 dermatomal distribution.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.