What is the most common cause of bradycardia in adults?

Bradycardia in adults is most commonly caused by heart block, which is a condition that affects the electrical conduction system of the heart, leading to slower heart rates. Heart block occurs when the signals that direct the heart to beat are disrupted. This can happen at various levels within the heart's conduction system, commonly at the atrioventricular (AV) node, resulting in a significantly slower heart rate, which is characteristic of bradycardia.

While increased physical fitness can lead to lower resting heart rates, especially in well-trained athletes, it does not typically cause bradycardia that necessitates clinical concern. Anxiety and hypothyroidism can also affect heart rate; however, they are not as prevalent as heart block when considering the entire adult population. Anxiety may occasionally lead to fluctuations in heart rate, but it often does not cause sustained bradycardia. Similarly, hypothyroidism can decrease heart rate but is considered less common than heart block as a primary cause of bradycardia in the general adult population. Therefore, heart block stands out as the most frequent underlying issue leading to bradycardia among adults.