Which complication is associated with untreated third-degree AV block?

Untreated third-degree AV block, also known as complete heart block, occurs when there is a complete failure of electrical conduction between the atria and ventricles. This results in the atria and ventricles beating independently of each other, often leading to a significantly reduced heart rate and inefficient cardiac output.

The major risk associated with untreated third-degree AV block is the potential for sudden cardiac arrest. This can occur due to the heart's inability to sufficiently pump blood, which may lead to inadequate perfusion of vital organs, resulting in syncope (loss of consciousness) or even death. The lack of coordination between atrial and ventricular contractions can also predispose patients to the development of life-threatening arrhythmias.

While other complications can arise as a result of the underlying pathophysiology or due to prolonged untreated block, sudden cardiac arrest is the most immediate and severe risk when there is a failure to restore normal conduction, making it critically important to recognize and treat this condition promptly.