The Role of Inotropic Variation in Ventricular Function during Atrial Fibrillation

upon intact anesthetized dogs to determine the rele-vance of a variety of hemodynamic variables to the ir-regular ventricular performance associated with atrial fibrillation. During experimentally induced atrial fibril-lation central aortic pulse pressure was measured in relation to the duration of the preceding diastolic inter-val, the relative degree of cycle-length change, the mag-nitude of the preceding aortic end-diastolic pressure, the rate of ventricular tension development (at a fixed diastolic tension), and to ventricular end-diastolic pres-sure. While all of the latter variables bore a significant relation to the chosen parameters of ventricular function, the most linear correlation lay with the rate of ventricu-lar tension development. It has been suggested, as a con-sequence, that the irregular ventricular performance ob-served during atrial fibrillation under these experimental conditions, may be more directly related to variation in the inotropic state of the ventricular myocardium than to an expression of the Frank-Starling concept, resulting from variable ventricular filling. The lability of the inotropic or contractile state has in turn been attributed to abrupt cycle-length change effecting inotropic al-teration analogous to postextrasystolic potentiation of contractility and, at rapid rates, effecting an alternation of the contractile state