EVIDENCE FOR AN INFLUENCE OF MECHANICAL RESTITUTION ON BEAT-TO-BEAT VARIATIONS IN HEMODYNAMICS DURING CHRONIC ATRIAL-FIBRILLATION IN PATIENTS

Objective: We tested the hypothesis that beat-to-beat changes in haemo dynamics during atrial fibrillation include an effect of each precedin g R-R interval through the interval-strength relationship (mechanical restitution). Background: The variation in stroke volume and pulse pre ssure characteristic of atrial fibrillation is usually ascribed to tim e dependent ventricular filling. Methods: We measured the maximum rate of rise of left ventricular pressure (LVdP/dt(max)), and aortic blood velocity and its integral in patients with atrial fibrillation underg oing cardiac catheterisation. The contractile response of isometric hu man myocardial trabeculae to sequences of atrial fibrillation was also studied, using the recorded ECGs as stimuli. The trabeculae were obta ined from the resected right ventricular outflow tracts of patients wi th Fallot's tetralogy undergoing operative correction. Results: Beat-t o-beat variations in contractile function during atrial fibrillation i n the patients were recorded as LVdP/dt(max) and left ventricular ejec tion (ascending aortic) velocity integral (proportional to stroke volu me). Both these indices correlated well with the response to the same ECG (R wave) sequences in the isometric model measured as the maximum rate of rise of force. dF/dt(max), r = 0.72 to 0.81, p < 0.0001. When short pre-preceding intervals were excluded (minimizing the effect of post-extrasystolic potentiation), these variables showed a positive cu rvilinear relationship to preceding interval typical of mechanical res titution. Conclusions: Mechanical restitution, which causes beat-to-be at changes in inotropic state, accounts in part for the changes in str oke volume in atrial fibrillation. (C) 1998 Elsevier Science B.V.