Does a Sodium-Free Buffer Affect QRS Width in Experimental Amitriptyline Overdose?, ,

Study objectives: We carried out this study to determine the effects of pH alteration on QRS width with administration of tromethamine, a non-sodium-containing buffering agent, in experimental amitriptyline overdose. Design: Prospective, nonblinded trial. Participants: Adult mongrel dogs. Interventions: Pentobarbital-anesthetized dogs were overdosed with amitriptyline 5 mg/kg followed by infusion at 1.0 mg/kg/minute until the QRS width doubled, then decreased to .5 mg/kg/minute until the end of the experiment. At two defined points of toxicity, the dose of tromethamine required to raise the pH to 7.50±.4 was given. pH and QRS width at a speed of 100 mm/second were measured over a 30-minute period after each tromethamine dose. Data were analyzed with non-linear-regression analysis. Results: At toxicity 1 the mean pH was 7.32, with a QRS width of 11.6 mm. Two minutes after the tromethamine dose the pH rose to 7.51, with narrowing of the QRS width to 8.4 mm. At toxicity 2 the pH was 7.40, with QRS width of 10.6 mm. Two minutes after tromethamine, the pH rose to 7.49 and the QRS width decreased to 9.7 mm. Regression analysis showed a correlation between pH and QRS width; as pH increased, QRS width decreased (P=.0001). Conclusion: Cardiac toxicity of amitriptyline overdose, as manifested by QRS widening, is reversible by pH changes alone. [Stone CK, Kraemer CM, Carroll R, Low R: Does a sodium-free buffer affect QRS width in experimental amitriptyline overdose? Ann Emerg Med July 1995;26:58-64.]