VENTRICULAR CONTRACTILITY IN ATRIAL-FIBRILLATION IS PREDICTABLE BY MECHANICAL RESTITUTION AND POTENTIATION

We recently found that contractility (E-max) of an individual irregula rly arrhythmic beat in electrically induced atrial fibrillation (AF) i s reasonably predictable from the ratio of the preceding beat interval (RR1) to the beat interval immediately preceding RR1 (RR2) in the can ine left ventricle. Moreover, the monotonically increasing relation be tween E-max and the RR1-to-RR2 ratio (RR1/RR2) passed through or by th e mean arrhythmic beat E,, as well as the regular beat E-max at RR1/RR 2 = 1. We hypothesized that this E-max-RR1/RR2 relation during irregul ar arrhythmia could be attributed to the basic characteristics of the mechanical restitution and potentiation. To test this, we adopted a kn own comprehensive equation describing the force restitution and potent iation as a function of two preceding beat intervals and simulated con tractilities of irregular arrhythmic beats with randomized beat interv als on a computer. The simulated E-max-RR1/RR2 relation reasonably res embled the one that we recently observed experimentally, supporting ou r hypothesis. We therefore conclude that the primary mechanism underly ing the varying contractilities of irregular beats in AF is mechanical restitution and potentiation.