Norepinephrine prevents the adverse effects of lidocaine upon the heart. An experimental study in isolated guinea-pig hearts.

The adverse effects of local anesthetics associated with catecholamines upon the cardiovascular system, such as arterial pressure alterations and cardiac arrhythmias, have been highly discussed in pharmacological literature. When present in the blood circulation, the anesthetic salt promotes depressing effects at the cardiovascular system level, whilst the catecholaminic vasoconstrictors promote opposite effects upon the cardiovascular system. This paper aimed to verify which component is responsible for the initial effect upon the isolated heart of the guinea-pig by comparing the same anesthetic with and without vasoconstrictor. Guinea-pig hearts perfused using the Langendorff method received separate injections of lidocaine hydrochloride, without vasoconstrictor (LC), and with the vasoconstrictor norepinephrine at 1 : 50,000 (LCN) in doses of 3, 4 and 5 mg. LC was seen to significantly reduce the contraction force (CF) and the cardiac rate (CR) at all injected doses and at all times registered. LCN, though, significantly reduced CF in all doses only at 15 s after administration. At 30 and 60 s, LCN elevated CF to values close to those of the control. LCN in its 3 mg dose significantly increased CR at 30 and 60 s; with the 4 mg dose, significant alterations did not occur in CR and with the 5 mg dose CR was reduced significantly at 15 and 30 s, returning to values close to those of the control at 60 s. The electrocardiographic traces with LCN were similar to those with LC with a reduction occurring in the automatism of the sinus node, prolongation of the PR interval and widening of QRS, with all doses utilized at 15 s. Soon after the administration of LC and LCN ventricular asystole occurred, having a larger duration with LC. This duration was also increased when higher doses of anesthetics were used. The authors concluded that the initial cardio-depression effect of local anesthetics, with the vasoconstrictor norepinephrine, in the isolated guinea-pig heart is due to the anesthetic salt and that the vasoconstrictor exerts a protecting action against this effect.