Research we funded reveals for the first time a mechanism explaining why fatal heart rhythm disorders are more likely to occur in the morning when people wake up after a night’s sleep. These disorders, known as ventricular arrhythmias, are associated with a natural increase in the stress hormone cortisol, which peaks in the blood first thing in the morning.

In studies using mice, Researchers at Imperial College London have discovered that cortisol binds to specific proteins on the surface of heart cells.. The protein moves to another part of the cell, where it affects genes that control how easily heart cells transmit electrical signals that tell them to beat.

When the gene’s activity changes, the electrical impulses to the heart become less regular and more chaotic, causing an abnormal heart rhythm or arrhythmia.

The circadian rhythm, or day-night rhythm, of cortisol is influenced by sleep, with cortisol increasing minutes before a person wakes up.

Professor James Leiper, Associate Medical Director, said: “Ventricular arrhythmias can occur at any time and, if left untreated, can lead to loss of consciousness, sudden cardiac arrest, and death. To take steps to prevent these arrhythmias, It is important to continue to investigate the causes of arrhythmias.”

“This interesting study in mice reveals a possible solution to the mystery of why ventricular arrhythmias are more likely to occur in the morning. We may be able to explore new treatment options that can reduce arrhythmias in people who suffer from arrhythmias.Further research is needed to establish whether these findings are also seen in humans.”

The discovery of this association also raises the possibility of new treatments in this field. DD’Souza et al. further showed that injecting mice with a drug that blocks cortisol receptors prevented morning changes in ion channels, and therefore vulnerability to morning heart rhythm disturbances.

Lead researcher Alicia D’Souza, BHF Fellow at Imperial’s National Heart and Lung Institute, said: Our ancient circadian rhythms, which have evolved over millions of years, make us more vulnerable first thing in the morning.

“This is common to all species, so although our study focuses on mice, we believe this can also be directly applied to human and mammalian hearts.”

The study, led by Dr D’Souza and Professor Mark Boyett from the University of Bradford, investigated why the heart’s electrical activity exhibits a significant day-night rhythm, and why the heart is vulnerable to various day-night arrhythmias. This is the latest in the series. Different times of the day and night.

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