This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Local and Regional Anesthesia), Subject name: Anaesthesia
Which one of the following local anesthetics is highly cardio-toxic: 
Select and explain. 
A. Lignocaine, B. Procaine, C. Mepivacaine, D. Bupivacaine
D: Bupivacaine
Answer: D: Bupivacaine 
Explanation: Ans. is 'd' i.e., Bupivacaine Local anaesthetics are cardiac depressants but no significant effects are observed at conventional doses.At higher doses or on inadvertent i.v. injection they have quinidine like effect on heart i.e. they -Decrease automaticity Decrease excitability Decrease contractility Decrease conductivity Increase effective refractory periodAt a very high plasma concentration, some local anaesthetics can markedly alter electrophysiological properties of heart and they can themselves induce cardiac arrhythmias.Bupivacaine is the most cardiotoxic local anaesthetic and it can produce arrhythmias and severe cardiotoxic reactions which areA. V. heart blockDysrhythmias such as ventricular fibrillationCirculatory collapse (This occurs due to smooth muscle dilatation)