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Published on: January 24, 2013
Circadian variation in human ventricular refractoriness
T Q Kong1, J J Goldberger, M Parker
1Department of Internal Medicine, Northwestern University Medical School, Chicago, Ill., USA.
Circulation
|September 15, 1995
Summary
Sudden cardiac death risk is highest in the morning. This study found that ventricular refractory periods, crucial for heart rhythm, show a daily variation, peaking in the early morning. Beta-blockers normalize these periods.
Area of Science:
- Cardiology
- Circadian Biology
- Electrophysiology
Background:
- Sudden cardiac death incidence peaks in the morning.
- Circadian variation in myocardial ischemia is a potential factor.
- The role of circadian variation in ventricular refractoriness remains unclear.
Purpose of the Study:
- To investigate the existence of a circadian variation in ventricular refractoriness.
- To determine if this variation correlates with the increased morning incidence of sudden cardiac death.
Main Methods:
- Ventricular effective refractory periods were measured hourly over 24 hours in nine subjects with conduction system disease.
- Autonomic nervous system function was assessed.
- Measurements were repeated during beta-blockade in a subset of subjects.
Main Results:
- A significant circadian variation in ventricular refractoriness was observed.
- Shortest refractory periods occurred within 2 hours of waking.
- Beta-blockade abolished this circadian variation.
- Time of day, not catecholamine levels, was the independent predictor of refractory periods.
Conclusions:
- A significant circadian variation in ventricular refractory periods exists.
- Shortest refractory periods and maximal shortening occur in the early morning.
- Beta-adrenergic tone fluctuations largely drive this phenomenon.
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