ANALYSIS OF LEFT-VENTRICULAR CONTRACTILE BEHAVIOR DURING ATRIAL-FIBRILLATION

Objectives: The purpose of this study was to explore the physiology un derlying the beat-to-beat variations of ventricular function during at rial fibrillation (AF). Methods: Left ventricular pressure, and its fi rst derivative (LVdP/dt(max) an index of contractility, and aortic blo od velocity (and its integral AVI, an ejection index), were recorded u sing cathetermounted transducers in 15 patients with AF during cardiac catheterisation. Transfer function modelling was used to examine the influence of preceding intervals on LVdP/dt(max), and of LVdP/dt(max) on AVI. The technique also allowed simulation of the behaviour of LVdP /dt(max) in response to specific manipulations of interval. Results: T he variations in LVdP/dt(max) recorded from the AF patients were shown to be dependent on up to six preceding intervals; a maximum of 91% of the variation was explicable in this way. The influences of mechanica l restitution (MR, the relationship between preceding interval and con tractility), postextrasystolic potentiation (PESP, the inverse relatio nship between pre-preceding interval and contractility) and the decay of that potentiation were all demonstrated. These influences collectiv ely appeared to be powerful determinants of AVI. Simulations of LVdP/d t(max), following single interval perturbations, were entirely consist ent with these interval force effects. Conclusions: The cardiac interv al force relationship in man is an important determinant of the beat-t o-beat variations of contractile and ejection function during AF: the beat-to-beat variations in contractile (or inotropic) function are ind ependent of changes in ventricular filling or fibre-length.