How much does atrial fibrillation (A fib) decrease ventricular filling in percentage?

Atrial fibrillation (A fib) significantly impacts ventricular filling due to the loss of coordinated atrial contraction, which plays a crucial role in optimally filling the ventricles. In a healthy heart, the atria contract in sync with ventricular filling, facilitating the final phase of diastolic filling known as the atrial kick. However, in patients with A fib, this coordinated contraction is lost, which leads to a reduction in the efficiency of ventricular filling.

The decrease in ventricular filling is reported to be in the range of 20-25%. This is largely attributed to the rapid and irregular ventricular response that often accompanies A fib, which decreases the time available for diastolic filling. The subsequent decrease in end-diastolic volume can impact cardiac output, particularly in patients with existing cardiac conditions, leading to symptoms of heart failure or reduced exercise tolerance. Therefore, understanding that the ventricular filling is reduced by 20-25% during A fib is vital for managing patients with this arrhythmia.