Which of the following is a common cause of atrioventricular (AV) blocks?

Atrioventricular (AV) blocks occur when there is a disruption in the electrical signals that coordinate the heart's rhythm, specifically at the junction between the atria and ventricles. Age and myocardial infarction are both significant risk factors for developing AV blocks.

As individuals age, the myocardial tissues may undergo degenerative changes that impair conduction pathways. Myocardial infarctions can damage the conduction system, particularly if the lesion affects the heart's electrical structures. The impact on the heart's conduction system from these factors can lead to varying degrees of AV block, from first-degree to complete heart block. This makes age and a history of myocardial infarction common and clinically relevant causes of AV block.

While vascular diseases, valvular heart disease, and electrolyte imbalances can contribute to various cardiac issues, they are not as directly associated with the primary conduction disturbance seen in AV block as age and myocardial damage are.