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Cardiovascular Research 1998 38(1):82-90; doi:10.1016/S0008-6363(97)00318-0
© 1998 by European Society of Cardiology
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Copyright © 1998, European Society of Cardiology

Evidence for an influence of mechanical restitution on beat-to-beat variations in haemodynamics during chronic atrial fibrillation in patients

Suzanna M.C Hardman*, Mark I.M Noble, Tony Biggs and W.Anthony Seed

Department of Cardiopulmonary Medicine, Imperial College School of Medicine, Charing Cross Hospital, Fulham Palace Rd., London W6 8RF, UK

* Corresponding author. Present address: University College London Medical School (Whittington campus), Academic and Clinical Department of Cardiovascular Medicine, St Mary's Wing, Whittington Hospital, Highgate Hill, London N19 5NF, UK.

Objective: We tested the hypothesis that beat-to-beat changes in haemodynamics during atrial fibrillation include an effect of each preceding R–R interval through the interval–strength relationship (mechanical restitution). Background: The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time dependent ventricular filling. Methods: We measured the maximum rate of rise of left ventricular pressure (LVdP/dtmax), and aortic blood velocity and its integral in patients with atrial fibrillation undergoing cardiac catheterisation. The contractile response of isometric human myocardial trabeculae to sequences of atrial fibrillation was also studied, using the recorded ECGs as stimuli. The trabeculae were obtained from the resected right ventricular outflow tracts of patients with Fallot's tetralogy undergoing operative correction. Results: Beat-to-beat variations in contractile function during atrial fibrillation in the patients were recorded as LVdP/dtmax and left ventricular ejection (ascending aortic) velocity integral (proportional to stroke volume). 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/dtmax, 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 curvilinear relationship to preceding interval typical of mechanical restitution. Conclusions: Mechanical restitution, which causes beat-to-beat changes in inotropic state, accounts in part for the changes in stroke volume in atrial fibrillation.

KEYWORDS Mechanical restitution; Postextrasystolic potentiation; Frank–Starling mechanism; Ejection function


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