Does our heart have an internal clock that sets its rhythm?

Why do bradyarrhythmias occur at night? An intrinsic circadian clock in the cardiac conduction system?

Professor Mark Boyett wants to find out if the day-night cycle affects heart rhythm. A healthy heart steadily pumps blood around the body. An abnormal heart rhythm that is irregular, or is too fast or too slow is called an arrhythmia. If an arrhythmia is severe it can be life threatening. One type, called bradyarrhythmia (in its most severe form called heart block) causes a slow heart rate and tends to be more common at night. Until now scientists have thought this is due to nerve action on the heart, but it is now thought that some arrhythmias are the result of a ‘circadian clock’ in the heart. We already know there is a circadian clock in the brain that controls our sleep-wake cycle. Professor Boyett believes the heart’s circadian clock influences protein ion channels that control the heartbeat and could explain why bradyarrhythmias are more common at night. In this project, Professor Boyett will measure key proteins in areas of the heart of mice important for heart rate control at different times over 24 hours to see if there are any oscillations between night and day and if they could be responsible for night bradyarrhythmias. This work will shed new light on the influence of sleep and wakefulness on an important type of heart rhythm disturbance, and may reveal new ways to treat arrhythmias.