Sleep and coronary heart disease

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Abstract
The relations of sleep and cardiovascular functions are not clear. Cardiac output tends to decrease during sleep in general, but during REM sleep arterial pressure and heart and respiratory rates vary. Occasionally systolic pressure may exceed daytime values. In general, the reduced sympathetic activity during sleep decreases the vulnerability of the heart to ventricular premature beats and tachycardias. Bradyarrhythmias and conduction blocks, on the other hand, are fairly common, especially during REM sleep. Usually these arrhythmias are not dangerous, and there is no risk in dreaming a lot. However, in some pathological conditions, eg among patients with severe coronary heart disease, an imbalance of vagal and sympathetic activity might contribute to fatal arrhythmias. In practice, this means that in such conditions it might be wise to avoid REM‐rebounds with nightmares, eg after sudden cessation of use of sedative drugs or alcohol. Sleep hypoxaemia due to apnoeas, and secondary cardiac arrhythmias, might explain some cases of nocturnal sudden deaths. Habitually snoring obese men have an elevated risk of obstructive sleep apnoeas. It remains to be studied whether habitual snorers and patients with sleep apnoeas have a higher risk of myocardial infarction than occasional snorers.