Circadian variations have been note...

Circadian variations have been noted in the oftenness of acute myocardial infarctions (MIs). The risk of acute MI appears to be higher between the hours of 6 a.m. and 12 noon than in any remaining six-hour period of the day. Because plaque break and subsequent thrombosis, is a major cause of acute MI, it is presum that plaque fracture also occurs in a similar rhythm

Tanaka and associates studied patients with acute MI who had preinterventional intravascular ultrasonography (IVUS) within 12 hours of the attack of acute MI symptoms. This conduct allows a clear distinction to be seen between plaque breach and nonrupture.

The authors studied 174 patients. Plaque break was noted in 81 (47 percent) while nonrupture was noted in the remaining 93 (53 percent) The charge of acute MI was significantly higher during the morning hours than during other periods. An associated increase in plaque quarrel also was noted during the morning hours. In the nonrupture arrange onset of acute MI was more common during sleep hours, between 12 midnight and 6 a.m.

The authors judge that a morning increase in plaque quarrel accounts for the characteristic circadian harmonious flow of acute MI. A variety of morning physiologic changes, including arterial constraining force surge accompanied by an increase in heart rate and vascular tone, and decreased serum cortisol on a levels may individually or in combination explain the increase in morning plaque contention events. The authors note that acute MIs in their couple study groups probably have different etiologies.

Tanaka A, et al. Circadian variation of plaque fracture in acute myocardial infarction. Am J Cardiol January 1 2004;93:1-5

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