Comparative Direct Effects of Lidocaine and Bupivacaine on Regional Myocardial Function in Dogs at Noncardiovascular Toxic Levels

Although it is well recognized that accidental intravascular injection of bupivacaine during regional anesthesia can cause severe circulatory collapse, the direct cardiac effects at concentrations below the cardiotoxic level have not been described, despite increased use of regional anesthesia and its combination with general anesthesia. Therefore, the author compared the direct effects of bupivacaine and lidocaine on regional myocardial function at such concentrations in in situ beating hearts in dogs. Regional myocardial function was assessed during selective intracoronary infusion of lidocaine (0, 2, 5, 10, and 20 micrograms/mL in plasma) or bupivacaine (0, 0.5, 1.25, 2.5, and 5.0 micrograms/mL in plasma), while the left anterior descending coronary artery was perfused at constant flow with blood from the femoral artery. Lidocaine had a myocardial depressant effect (systolic shortening) at plasma concentrations greater than 10 micrograms/mL, whereas bupivacaine began to depress regional myocardial function at concentrations greater than 2.5 micrograms/mL. There was also a widening of the QRS interval during bupivacaine infusion at those concentrations. Post-systolic shortening was more frequent during bupivacaine infusion (47.0% +/- 7.7%) at the plasma concentration (5 micrograms/mL) than during lidocaine infusion (33.2% +/- 7.4%) at the corresponding concentration (20 micrograms/mL). It is concluded that, although lidocaine and bupivacaine have no direct myocardial effects at clinical levels (below 5 micrograms/mL and 1.25 microgram/mL lidocaine and bupivacaine, respectively), they depress myocardial function at plasma concentrations near the cardiotoxic level with a relative toxicity ratio (1:4). This effect is more pronounced with bupivacaine at higher concentrations (> 5 micrograms/mL) than with lidocaine at corresponding concentrations (> 20 micrograms/mL).