Left ventricular beat to beat performance in atrial fibrillation: dependence on contractility, preload, and afterload

Objective-To assess independent determinants of beat to beat variation in l eft ventricular performance during atrial fibrillation. Design-Prospective study. Setting-University hospital. Patients-Seven patients with chronic non-valvar atrial fibrillation. Interventions-Invasive and non-invasive haemodynamic variables were assesse d using a non-imaging computerised nuclear probe, a balloon tipped flow dir ected catheter, and a non-invasive fingertip blood pressure measurement sys tem linked to a personal computer. Main outcome measures-left ventricular ejection fraction, left: ventricular volume, ventricular cycle length, pulmonary capillary wedge pressure, and measures of left ventricular afterload (end systolic pressure/stroke volume ) and contractility (end systolic pressure/end systolic volume) were calcul ated on a beat to beat basis during 500 consecutive RR intervals. A statist ical model of the beat to beat variation of the ejection fraction containin g these variables was constructed by multiple regression analysis. Results-Positive independent relations with ejection fraction were found fo r preceding RR interval, contractility, and end diastolic volume, while inv erse relations were found for afterload, preceding end systolic volume, and preceding contractility (all variables, p < 0.0001). A relatively strong i nteraction was found between end diastolic volume and afterload, indicating that ejection fraction was relatively more enhanced by preload in the pres ence of low afterload. Conclusions-The varying left ventricular systolic performance during atrial fibrillation is independently influenced by beat to beat variation in cycl e length, preload, afterload, and contractility. Beat to beat variation in preload shows its effect on ventricular performance mainly in the presence of a low afterload.