Electrophysiologic effects of Tween 80 in the myocardium and specialized conduction system of the canine heart.

Amiodarone, a wide spectrum antiarrhythmic agent, has been associated with hypotensive reactions in man as well as in dogs after intravenous use. This hypotensive effect has been attributed to Tween 80, the diluent in the commercially available form of amiodarone. We studied the electrophysiologic effects of Tween 80 in the cardiac conduction system of the dog. Electrophysiologic studies were conducted in anesthetized adult dogs before and after the administration of 10 and 20 mg/kg of Tween 80, equivalent to the amount of diluent in 5 and 10 mg/kg respectively of commercial intravenous amiodarone. In addition to a drop of 60% in systolic blood pressure and 66% in diastolic blood pressure (p less than 0.005), 10 mg/kg of Tween 80 induced a decrease in heart rate (sinus cycle length increased from 523 +/- 57 msec to 662 +/- 27 msec, p less than 0.025), prolongation of sinus node recovery time (652 +/- 77 msec to 804 +/- 45 msec, p less than 0.05), depression of AV nodal function manifested by induction of Wenckebach at longer cycle length (from 208 +/- 18 msec to 266 +/- 14 msec, p less than 0.005), and increase in atrial ERP (from 138 +/- 7 msec to 176 +/- 14 msec, p less than 0.025) and FRP (from 180 +/- 14 msec to 209 +/- 12 msec, p less than 0.025). No further significant changes were observed after the second Tween 80 dose. The ventricular ERP increased significantly (from 168 +/- 18 msec to 20 +/- 16 msec, p less than 0.025) following the 20 mg/kg dose. It is demonstrated that Tween 80 is a potent depressant of the cardiac conduction system in the dog, capable of causing electrophysiologic changes similar to those produced by amiodarone in humans and dogs.