Background Cardiotoxicity is the most severe complication of long-acting local anesthetics. The aim of this trial is to compare early signs of depression of cardiac conduction linked with the administration of either ropivacaine or bupivacaine for interscalene block.

Methods Thirty-two patients (American Society of Anesthesiologists I/II) scheduled for elective shoulder arthroscopy were prospectively enrolled to receive, in a randomized and double-blind fashion, either 40 mL of ropivacaine 5 mg/mL or 40 mL of bupivacaine 5 mg/mL for interscalene block. Holter monitoring was started the night before surgery and continued until the end of the study. Peripheral blood sampling was performed before administration of local anesthetics (= baseline) and 15, 20, 25, 30, 35, 40, 45, 60, and 360 minutes after completion of the interscalene block for measurement of total and unbound concentration of the 2 local anesthetics. Alpha-1-acid-glycoprotein was measured at baseline, t₃₀, and t₃₆₀.

Results All anesthetic blocks in both groups were successful and comparable. Electrocardiographic recordings for QRS, QT, and QTC intervals did not change and were similar in both groups. In the bupivacaine group, significant prolongation of the PQ interval was noted 15 minutes after drug application and remained significantly prolonged until t₆₀. Total and unbound plasma local-anesthetic concentrations were comparable between both groups at all times. In both groups, local-anesthetic plasma mean levels reached a peak between 30 and 45 minutes after the bolus application. The highest mean plasma levels were 0.103 (±0.05) mg/L for unbound ropivacaine and 0.084 (±0.03) mg/L for unbound bupivacaine, which occurred in both groups at t₃₀.

Conclusions Electrocardiographic recordings were similar in both groups, except for a significant prolongation of the PQ interval in the bupivacaine group at plasma levels below threshold for cardiotoxicity.