What arrhythmia does a third-degree AV block indicate in a patient with a history of myocardial infarction?

A third-degree AV block, also known as complete heart block, indicates a significant disruption in the electrical conduction system of the heart. In this condition, there is no communication between the atria and the ventricles, which is often a result of damage to the conduction pathways, commonly seen after a myocardial infarction. This implies that the impulses generated in the atria do not reach the ventricles, which can lead to disparate heart rates for the two chambers.

In patients with a history of myocardial infarction, the presence of a third-degree AV block suggests underlying heart disease and can often be associated with ischemia or infarction affecting the coronary arteries. The result is a clinically significant arrhythmia characterized by a complete lack of coordination between atrial and ventricular rhythms. This type of block frequently requires immediate intervention, such as pacing, because it can be symptomatic and pose serious risks, such as bradycardia and resultant inadequate cardiac output.

The other options provided do not accurately describe the arrhythmia observed in third-degree AV block nor are they directly linked to the underlying conduction disturbances characterized by this type of block.