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

Abstract

Objective: To assess independent determinants of beat to beat variation in left 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 assessed using a non-imaging computerised nuclear probe, a balloon tipped flow directed catheter, and a non-invasive fingertip blood pressure measurement system 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 calculated on a beat to beat basis during 500 consecutive RR intervals. A statistical model of the beat to beat variation of the ejection fraction containing these variables was constructed by multiple regression analysis.

Results: Positive independent relations with ejection fraction were found for preceding RR interval, contractility, and end diastolic volume, while inverse relations were found for afterload, preceding end systolic volume, and preceding contractility (all variables, p < 0. 0001). A relatively strong interaction was found between end diastolic volume and afterload, indicating that ejection fraction was relatively more enhanced by preload in the presence of low afterload.

Conclusions: The varying left ventricular systolic performance during atrial fibrillation is independently influenced by beat to beat variation in cycle 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.

Figure 1

Schematic drawing showing the relation between the QRS complex on the ECG, the definition of the index interval, preceding and pre-preceding interval (pRR and ppRR, respectively), and the timing of the volume and pressure measurements. During the index interval, EDV (end diastolic volume), ESP (end systolic pressure), and ESV (end systolic volume) were measured. During the preceding interval, pEDV, pESP, and pESV (indicating preceding EDV, ESP, and ESV, respectively), and during the pre-preceding interval ppEDV, ppESP, and ppESV (indicating pre-preceding EDV, ESP, and ESV, respectively) were measured.

Figure 2

Positive relation between preceding RR interval and left ventricular (LV) ejection fraction in one of the patients. There is a curvilinear relation with ejection fraction, remaining rather constant at long RR intervals.

Figure 3

Positive relation between left ventricular (LV) end diastolic volume and LV ejection fraction in the same patient as in fig 2.

Figure 4

Example of the positive relation between left ventricular (LV) contractility of the index cycle (ESP/ESV indicates the ratio of end systolic pressure and end systolic volume) and LV ejection fraction in the same patient as in fig 2.

Figure 5

Example of the negative relation between left ventricular (LV) afterload of the index cycle (ESP/SV indicates the ratio of end systolic pressure and stroke volume) and LV ejection fraction.

Figure 6

Effect of the interaction between left ventricular (LV) afterload (ESP/SV indicates the ratio of end systolic pressure and stroke volume) and LV end diastolic volume (EDV) on LV ejection fraction. The curves are based on the multiple regression model. All other variables were fixed on their mean value. With rising afterload, ejection fraction decreases. The interaction shows that with low afterload, the effect of end diastolic volume on the ejection fraction is relatively large, whereas with high afterload the ejection fraction was relatively less influenced by end diastolic volume.