Treatment of ventricular tachyarrhythmias resulting from amitriptyline toxicity in dogs

This study was designed to analyze the effects of lidocaine and sodium bicarbonate on ventricular arrhythmias resulting from amitriptyline infusion in dogs. Amitriptyline was infused i.v. at 0.5 mg/kg/min for 30 min, followed by 1 mg/kg/min to dogs anesthetized with morphine and alpha-chloralose. When arrhythmia occurred, the infusion rate was reduced by one-third and the effect of various interventions studied. In the initial 18 dogs, lidocaine, sodium bicarbonate or isotonic saline was administered i.v. to six dogs each in a randomized, blinded fashion. The prevalence of ventricular ectopic complexes was not changed after isotonic saline, but was reduced by lidocaine at concentrations greater than or equal to 5 mg/l and by sodium bicarbonate. The effects of lidocaine were transient and associated with significant blood pressure reduction. Sodium bicarbonate produced more dramatic and sustained arrhythmia reversal along with a reduction in amitriptyline-induced conduction slowing. Administration of hypertonic sodium chloride in equimolar quantities to sodium bicarbonate failed to affect amitriptyline-induced ventricular arrhythmias significantly, but hyperventilation to a pH similar to that produced by sodium bicarbonate (7.48) significantly reduced the frequency of amitriptyline-induced ventricular ectopy. When amitriptyline was infused into dogs ventilated with various respiratory rates, ventricular arrhythmia resulted in 18 of 18 (100%) dogs with pH less than 7.42, 2 of 4 (50%) dogs with pH between 7.48 and 7.51 and 0 of 8 (0%) dogs with a pH between 7.59 and 7.65 (P less than or equal to .001). These results suggest that sodium bicarbonate is effective treatment for amitriptyline-induced cardiac arrhythmias with beneficial effects largely due to alkalinization.(ABSTRACT TRUNCATED AT 250 WORDS)