What is considered a complete heart block?

A complete heart block, also known as a third-degree atrioventricular (AV) block, occurs when there is a total failure of conduction between the atria and ventricles. In this condition, the electrical signals generated in the atria do not reach the ventricles at all, leading to a disconnection in the heart's electrical system. As a result, the atria and ventricles beat independently, which is referred to as AV dissociation.

This form of block is characterized by a complete absence of coordination between the atrial and ventricular rhythms. The atrial activity continues at its intrinsic rate, while the ventricles may generate a slower escape rhythm, often from the lower conduction pathways (such as the bundle of His or Purkinje fibers). This independent functioning can lead to significant hemodynamic instability, as the ventricles may not contract in synchrony with the atrial impulses, potentially resulting in inadequate cardiac output.

In the context of the other choices: atrial flutter represents a distinct arrhythmia characterized by rapid, organized atrial contractions; second-degree AV block indicates intermittent loss of conduction to the ventricles (either type I or type II), where some atrial beats are conducted to the ventricles while others are not