Influence of acetylcholine, isoproterenol, quinidine and ouabain on effective refractory periods of atrial and ventricular myocardium in the dog.

Acetylcholine-, isoproterenol-, quinidine- and ouabain-induced variations of the effective refractory periods (E.R.P.) of the non-specialized atrial and ventricular tissue have been explored in the dog by the extra-stimulus method during total cardiopulmonary by-pass. Acetylcholine significantly shortens the E.R.P. of atrial fibers, but does not provoke any change in the ventricular tissue, whereas a parallel decrease of atrial and ventricular E.R.P. is noted with isoproterenol. Quinidine induces a larger increase of the E.R.P. in the atrium than in the ventricle. The ouabain-induced shortening of the E.R.P. in the atrium is more marked than in the ventricle but is followed by a secondary increase which depends on both time after injection and dose. Hypotheses about the mechanisms of these effects, their importance in fibrillation and their relation to clinical uses are discussed.