How does atrial fibrillation affect cardiac output?

Atrial fibrillation, characterized by an irregular and often rapid heart rhythm, significantly impacts cardiac output primarily because the atria do not contract effectively. Instead of a coordinated contraction that helps propel blood into the ventricles, the atria quiver, leading to ineffective atrial contractions. This can decrease the overall amount of blood that fills the ventricles during diastole.

As a result, the ventricular filling may be compromised, particularly affecting the preload, which is the volume of blood in the ventricles before contraction. This inadequate preload can lead to a reduction in stroke volume, meaning that less blood is ejected with each heartbeat, ultimately decreasing cardiac output.

In individuals with atrial fibrillation, the loss of the atrial contraction often translates to a noticeable decline in cardiac efficiency, particularly during exertion or in patients with other underlying heart conditions. The irregular rhythm can also lead to a rapid ventricular response, further complicating the hemodynamic status and leading to symptoms of heart failure in some cases. Thus, the assertion that atrial fibrillation can result in decreased output due to ineffective atrial contraction accurately captures the physiological changes that occur during this arrhythmia.