In atrial fibrillation, what causes the irregular ventricular rhythm?

In atrial fibrillation, what causes the irregular ventricular rhythm?

• A. Random atrial depolarizations do not always reach the ventricles
• B. SA node firing too quickly
• C. P waves interfering with QRS complexes
• D. Ventricles contracting consistently

Answer: (A)

In atrial fibrillation, the irregular ventricular rhythm is primarily caused by random atrial depolarizations that do not always reach the ventricles. In this arrhythmia, the atria are not contracting effectively; instead, they quiver, leading to numerous chaotic electrical impulses. Due to the presence of these irregular impulses, not every signal is transmitted through the atrioventricular (AV) node to the ventricles. Consequently, the ventricular response becomes highly variable and irregular, resulting in the characteristic irregularly irregular rhythm seen on an EKG. This phenomenon explains why patients with atrial fibrillation often present with a rapid and erratic ventricular rate, which can fluctuate significantly.

The other options do not accurately represent the mechanism behind the irregular ventricular rhythm. An SA node firing too quickly would lead to a regular rhythm rather than an irregular one. P waves interfering with QRS complexes would occur in circumstances where both atrial and ventricular pacing occur, which is not the case in atrial fibrillation. Lastly, if the ventricles were contracting consistently, one would expect a regular rhythm rather than the distinct irregularity characteristic of atrial fibrillation. Thus, the correct answer captures the essence of this arrhythmia's impact on ventricular activity.