Why does heart block occur at night, especially in athletes?

Why does heart block occur at night (especially in athletes)?

The rate and rhythm of the heartbeat changes between night and day. In particular, at night there can be long pauses between heartbeats, known as ‘heart block’. This occurs in a specialised part of the heart called the atrioventricular (AV) node, but we know very little about how and why it happens. It is important to understand the causes of heart block because it can result in fainting, dizziness, fatigue, shortness of breath and chest pain. People with severe heart block need to be fitted with an electronic pacemaker and, surprisingly, the condition is more common in athletes. These researchers are investigating why heart block is more common at night and in athletes. They believe it is linked to our inbuilt body clock, known as the ‘circadian clock’, and due to changes in specialised proteins call ion channels, which are important in controlling the heartbeat. They will investigate this by measuring the activity of key genes in the AV node at different times. These genes are important for making the ‘parts’ of the circadian clock and for making the ion channel proteins. They will also investigate the effect of athletic training on the levels of the same key genes. By discovering what is responsible for heart block, we can develop new treatments to prevent it. For example, if heart block occurs at night because of the circadian clock, it might be possible to disrupt the clock in the AV node and prevent more serious heart block from occurring at night.