Cardiac Effects of Amitriptyline in Rats

Abstract

The effect of intravenous amitriptyline (0.5–2 mg/kg) on heart rate, blood pressure, ECG, and electrolytes in plasma and heart muscle was studied in rats. In addition, the effect on monophasic action potentials was studied in rats with open chest. Amitriptyline caused a significant decrease in blood pressure and heart rate and a significant prolongation of QRS and PQ duration. At the time of maximal QRS prolongation (mean +94%) the duration of monophasic action potentials was virtually unchanged. Beta-adrenergic blockade by means of pretreatment with 0.1 mg propranolol did not influence the amitriptyline-induced prolongation of QRS duration. Amitriptyline administration causing obvious QRS prolongation induced no detectable changes in plasma and heart muscle electrolytes. The results contradict adrenergic dominance or marked imbalance between intra- and extra-cellular electrolytes as a cause of the ECG changes. The present data indicate that the amitriptyline effect is compatible with a direct quinidine-like action on the heart, resulting mainly in a slowing of impulse propagation in the intracardiac conduction system.

Key Words:

• Action potential
• adrenergic beta-receptor blockade
• amitriptyline
• blood pressure
• electrocardiography