Final answer:
Headache is not a symptom of local anesthetic toxicity. Symptoms of toxicity include tinnitus, seizures, agitation, and cardiac arrhythmias. Lidocaine blocks sodium channels to prevent pain signal transmission.
Step-by-step explanation:
The symptom that is NOT a symptom of local anesthetic toxicity from the choices provided is Headache (A). Local anesthetic systemic toxicity (LAST) symptoms are due to the effect of anesthetics on the central nervous system and cardiovascular system. These symptoms include tinnitus (B), seizures (C), agitation (D), and cardiac arrhythmias (E). Lidocaine, a common local anesthetic, works by blocking the sodium channels in the neuronal cell membrane, which prevents the propagation of action potentials. This leads to the absence of pain because the nerves are unable to transmit pain signals to the brain.