Sudden cardiac death depending on the time of day

Study: Heart attack risk highest in the morning

23.02.2012

The risk of a heart attack varies during the day. The reason for this is a molecular relationship between the occurrence of cardiac arrhythmias and the day-night rhythm, report US researchers at the University "Case Western Reserve" in Cleveland (Ohio) in the journal „Nature“.

The scientists around Mukesh Jain from the University of Case Western Reserve found in their experiments on mice a clear molecular relationship between the occurrence of so-called ventricular arrhythmias and the day-night rhythm. This causes a higher heart attack risk in the morning and in the evening, write the US scientists.

Heart attack risk varies with the course of the day
In the course of their investigations, the researchers have tried to get to the bottom of the statistically significant risk of heart attack during the course of the day. To the suspected connection with the „internal clock“ In order to analyze humans, US scientists examined various factors, such as hormone release, metabolism and the sleep-wake cycle, which are associated with the human's 24-hour rhythm. Mukesh Jain and colleagues came across the transmission factor Klf15 (crippling-like factor 15), whose essential influence on the 24-hour rhythm was already known from previous investigations. According to the research group, Klf15 has a significant effect on the heartbeat by regulating, as a transcription factor with the help of a protein, the inflow of potassium via the so-called cardiac ion channel into the heart muscle cells.

Molecular relationship between the heart rhythm and the internal clock
To test the effect of the transcription factor on the electrical stability of the heartbeat, US scientists bred genetically modified mice that either lacked or contained a significant excess of Klf15. Both a deficiency and an excess of Klf15 resulted in the loss of rhythmic stability of the heartbeat and of the animals „increased susceptibility to ventricular arrhythmias“, write the scientists. The rodents were therefore significantly more likely to die as a result of cardiac arrhythmias. Since the level of the transcription factor fluctuates during the course of the day, this is also a possible explanation for the risk of sudden cardiac death, which is significantly higher in the morning and slightly higher in the evening, Mukesh Jain and colleagues report. First, according to the US researchers, the proof of a molecular relationship between the occurrence of cardiac arrhythmias and the „internal clock“ succeeded - but so far only in mice.

In further studies, it would now be necessary to check "whether the same correlation exists between the risk of cardiac arrhythmias and the transcription factor Klf15 in humans," explained Mukesh Jain. However, the "fluctuating probability of sudden cardiac death during the course of the day suggests that there is a similar molecular relationship between the biological clock and the cardiac arrhythmia in humans," the researchers concluded in the study report. Other research also indicates that a heart attack in the morning is usually worse than in the evening. (Fp)

Read about heart attack:
Stress in the job leads to a heart attack
Stress & anger worsens heart attack prognosis
Often no heart attack diagnosis by ECG
Anti-inflammatory protein after myocardial infarction
Heart attack worse in the morning than in the evening