It would be interesting to find out the details of this incident. How much lidocaine was actually injected? It didn’t sound like an allergic reaction per se, more like a toxic overdose which is known to cause seizures and cardiac arrest. A local injection in excess of the recommended dose can lead to toxic blood levels which and cause seizures, and at higher levels, cardiac arrest. http://rebelem.com/local-anesthetic-systemic-toxicity-last/