Relationship between atrial and ventricular rates of fibrillation and cardiac contractile tissue effective refractory periods in the dog.

1 During total cardiopulmonary bypass, acetylcholine-, isoprenaline-, ouabain- and quinidine-induced variations in the atrial and ventricular rates of fibrillation were studied and compared with the variations in effective refractory periods (ERP) of atrial and ventricular contractile tissue obtained under the same experimental conditions. 2 Acetylcholine significantly shortened the ERP and accelerated the rate of fibrillation in the atrium but did not provoke any change in ventricular tissue. A parallel decrease in atrial and ventricular ERP and a parallel increase in atrial and ventricular rates of fibrillation were observed with isoprenaline. 3 Ouabain exerted a biphasic effect on the atrium, with an initial decrease in the ERP and an initial acceleration of the rate of fibrillation. It produced only a slight decrease in the ventricular ERP and no significant variation in the ventricular rate of fibrillation. 4 Quinidine induced a greater increase in the ERP and a greater slowing of the rate of fibrillation in the atrium than in the ventricle. 5 The variations in percentage change of refractoriness and rate of fibrillation were strictly correlated: r = 0.89 (P less than 0.001); the equation of the regression line was y = --0.86 x --2.98.