Most cardiotoxic local anaesthetic is
**Core Concept**
Bupivacaine is a long-acting local anesthetic that belongs to the amino amide class. Its cardiotoxicity is a well-known complication, particularly when administered in high doses or through accidental intravascular injection. The mechanism of cardiotoxicity involves the blockade of sodium channels, leading to a reduction in cardiac contractility and an increase in cardiac conduction time.
**Why the Correct Answer is Right**
Bupivacaine's cardiotoxicity is attributed to its high lipid solubility, which allows it to easily penetrate the cardiac cell membrane and bind to sodium channels. This binding causes a persistent blockade of sodium channels, leading to a decrease in the slope of the action potential and a reduction in cardiac contractility. Additionally, bupivacaine can also affect potassium channels, leading to an increase in cardiac conduction time and a predisposition to arrhythmias.
**Why Each Wrong Option is Incorrect**
**Option A:** Procaine is a short-acting local anesthetic that belongs to the ester class. It is less cardiotoxic than bupivacaine due to its lower lipid solubility and shorter duration of action.
**Option B:** Lidocaine is a short-acting local anesthetic that belongs to the amino amide class. While it can be cardiotoxic in high doses, it is less cardiotoxic than bupivacaine due to its lower affinity for sodium channels and its ability to act as a sodium channel blocker at lower concentrations.
**Option D:** Benzocaine is a short-acting local anesthetic that belongs to the ester class. It is less cardiotoxic than bupivacaine due to its lower lipid solubility and shorter duration of action.
**Clinical Pearl / High-Yield Fact**
To minimize the risk of cardiotoxicity when using bupivacaine, it is essential to use the lowest effective dose, to avoid accidental intravascular injection, and to monitor cardiac function closely during administration. Additionally, the use of epinephrine as a vasoconstrictor can help to reduce the systemic absorption of bupivacaine and minimize its cardiotoxic effects.
**Correct Answer: C. Bupivacaine. Bupivacaine is the most cardiotoxic local anesthetic.**