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Cambridge University Science Magazine
Circadian rhythms are known to act as intrinsic body clocks in controlling many daily physiological cycles. However, this is the first time that these rhythms have been shown to influence the beating of the heart, with potentially fatal consequences.

The contraction and relaxation of heart muscle is largely controlled by the flow of potassium in cardiac myocyte cells. This flow rate is determined by potassium channel interacting protein (KChIP2), which is itself controlled by another protein, krüppel-like factor 15 (Klf15). Importantly, the production of Klf15 fluctuates in accordance with the circadian clock, meaning that the circadian clock has direct influence over susceptibility of the heart to failure.

Scientists predict that variations in KChIP2 protein production are greatest in the morning. The effect of this variation in potassium channel function could be to alter the time window in which potassium is able stimulate the heart. This change in the time interval for repolarisation of the heart is linked to abnormal heart rhythms called arrhythmias. As the heart beat loses its regularity, the risk of sudden cardiac death is increased.

Studies in mice support this hypothesis, as both deficiency and excess of Klf15 protein caused inconsistency in cardiac repolarisation and greatly increased susceptibility to heart failure. Additionally, numerous epidemiological studies have demonstrated that cases of sudden cardiac death and heart failure follow a daily pattern, with a broad peak between 9 and 11am.

Therefore, the association between circadian rhythms and sudden cardiac death may not be trivial. It is hoped that subsequent research will shed further light on the factors that really could cause your heart to skip a beat.

Written by Zac Baynham-Herd