A mathematical model of left ventricular function in atrial fibrillation

Area of Science:

• Cardiology
• Cardiovascular Physiology
• Biomedical Engineering

Background:

• Atrial fibrillation (AF) presents irregular heart rhythms, complicating the assessment of cardiac output.
• Understanding beat-to-beat variations in left ventricular stroke output is crucial for managing AF patients.

Purpose of the Study:

• To investigate the relationship between R-R interval duration and left ventricular stroke output in patients with AF.
• To quantify the influence of preceding R-R intervals on stroke distance using Doppler ultrasound.

Main Methods:

• Doppler ultrasound was used to measure stroke distance (a surrogate for stroke volume) in 60 AF patients.
• Multiple regression analysis was employed to determine the correlation between stroke distance and preceding R-R intervals.
• Individual hemodynamic profiles were analyzed to understand variations in left ventricular function.

Main Results:

• Beat-to-beat variations in stroke distance were significantly explained by the two preceding R-R intervals (Mean R=0.82).
• A positive correlation was observed between stroke distance and the immediately preceding R-R interval (preload/diastolic filling).
• A negative correlation was noted with the second previous R-R interval, attributed to the force-frequency effect on contractility.

Conclusions:

• The preceding R-R interval (preload) and the second previous R-R interval (contractility) are key determinants of stroke distance in AF.
• The influence of preload decreases with declining left ventricular function and increasing heart rate.
• Individual hemodynamic profiles reveal significant variations in left ventricular response to R-R interval changes.