What is the medical term for cardiac activity where all atrial impulses are blocked at the AV junction, leading to independent beats of atria and ventricles?

The medical term for cardiac activity characterized by the complete blockage of all atrial impulses at the atrioventricular (AV) junction is indeed third-degree AV block, also known as complete heart block. In this condition, the electrical signals originating from the atria do not conduct to the ventricles, resulting in independent functioning of the atria and ventricles. The atria continue to beat at their inherent rate, while the ventricles take on a slower rhythm dictated by an alternate pacemaker, often located in the Bundle of His or purkinje fibers.

This disassociation between the atrial and ventricular activities is what marks third-degree AV block as distinct from other types of AV block, such as second-degree AV block, where some atrial impulses may still be conducted through the AV node to the ventricles. In third-degree AV block, there is no such communication, creating a clear and significant separation between the rhythms of the two parts of the heart, which can lead to various symptoms and may require medical intervention.

Other options like sinus arrhythmia or atrial fibrillation do not describe this complete block of signals but rather involve different mechanisms of rhythm irregularities.