Circadian variation in thrombotic risk factors in haemorrhagic cardiovascular events
Authors: Kazuomi Kario, Thomas G Pickering
Journal: The Lancet (1999)

Roberto Manfredini and colleagues (Feb 20, p 643)1Manfredini, R, Poraluppi F, Zamboni P, Salmi R, Gallerani M Circadian variation in spontaneous rupture of abdominal aorta.Lancet. 1999; 353: 643-644Summary Full Text Full Text PDF PubMed Scopus (69) Google Scholar report diurnal variation in spontaneous rupture of abdominal aorta. They found two prominent peaks, one in the morning at about 0800 h and the other at about 2000 h in the evening. Most atherothrombotic events, such as myocardial infarction and ischaemic stroke, have diurnal variation in their occurrences,2Muller JE Tofler GH Stone PH Circadian variation and triggers of onset of acute cardiovascular disease.Circulation. 1989; 79: 733-743Crossref PubMed Scopus (1233) Google Scholar but there is usually only one morning peak. Some studies show a second evening peak, but it is usually much less prominent than the morning peak. On the other hand, in addition to the first morning peak, the second peak in the evening has been more clearly shown in the occurrence of haemorrhagic cardiovascular events, such as subarachnoid haemorrhage, haemorrhagic stroke, and spontaneous rupture of thoracic aortic aneurysm, than in thrombotic disease.3Gallerani M Portaluppi F Maida G et al.Circadian and circannual rhythmicity in the occurrence of subarachnoid hemorrhage.Stroke. 1996; 27: 1793-1797Crossref PubMed Scopus (98) Google Scholar Manfredini and co-workers explain the peaks of the haemorrhagic events on the basis of the diurnal variation in blood pressure. However, their explanation is insufficient because there is usually no pronounced evening peak of blood pressure comparable with the morning peak, even allowing for the siesta dip in blood pressure reported in the early afternoon by some Italian studies.4Bursztyn M Mekler J Wachtel N Ben-Ishay D Siesta and ambulatory blood pressure monitoring.Am J Hypertens. 1994; 7: 217-221Crossref PubMed Scopus (99) Google Scholar We propose that the imbalance between blood pressure levels and thrombotic factors might explain the second peak of haemorrhagic episodes. Several factors that are direct triggers of atherothrombotic episodes have substantial diurnal variations. These factors include activation of platelets and increased blood viscosity, hypercoagulability, and hypofibrinolysis, all of which show peak activity in the morning and lowest levels in the late afternoon or evening.5Sayer JW Gutteridge C Syndercombe-Court D Wilkinson P Timmis AD Circadian activity of the endogenous fibrinolytic system in stable coronary artery disease: effects of betaaddrenoreceptor blockers and angiotensin-converting enzyme inhibitors.J Am Coll Cardiol. 1998; 32: 1962-1968Summary Full Text Full Text PDF PubMed Scopus (35) Google Scholar These diurnal changes of thrombotic risk factors may be expected to contribute to the peak of thrombotic episodes in the morning. For haemorrhagic events, however, the lower levels of these thrombotic factors in the evening combined with a persistence of a fairly high blood pressure until sleep might explain the second evening peak. Circadian variation in thrombotic risk factors in haemorrhagic cardiovascular eventsAuthors' reply Full-Text PDF