BOSTON, MASSACHUSETTS. Pulmonary embolism is a serious medical emergency in which a blood clot is carried in the circulation to lodge in the pulmonary artery. Pulmonary embolism (PE) is frequently fatal and often follows surgery. Researchers at the Harvard Medical School have discovered that 74 per cent of all cases of non-fatal PE events occur during the autumn and winter months and that 76 per cent of them occur in the morning hours with a peak at 8 AM. A similar event distribution has previously been noted for fatal PE and it is also known that the incidence of heart attack, stroke and sudden death peaks in the morning.
It is believed that the reason for this pattern relates to increased platelet aggregability and decreased antithrombin III levels and fibrinolytic activity in the morning hours. The researchers suggest that their findings can be used to help prevent PE after surgery. They suggest that subcutaneous heparin injections should be administered at 6 AM and 10 PM instead of at 9 AM and 6 PM as is the current practice.
Sharma, G.V.R.K., et al. Circadian and circannual rhythm of nonfatal pulmonary embolism. American Journal of Cardiology, Vol. 87, April 1, 2001, pp. 922- 24