[Differentiated circadian chrono-risk of acute myocardial infarct]

In order to determine whether acute myocardial infarction (AMI) presents a circadian periodicity in its occurrence, the onset of AMI, evaluated by onset of clinical symptoms and pain, has been analysed in 520 patients with AMI. The definitive criteria of AMI were: typical chest pain, electrocardiographic findings, and plasma CPK-MB elevation. All cases of AMI were divided into subgroups according to sex (males = 369, females = 151), age (less than 60 years old = 254, more than 60 years old = 266), type of AMI (Q wave AMI = 407, non Q wave AMI = 113), previous pharmacological treatment (no treated = 373, treated = 147), history of arterial blood hypertension (normotensive = 403, hypertensive = 117). Cases of Q and non Q wave AMI were also subdivided according to treatment and hypertensive conditions. All AMI occurred outside hospital; silent AMI and reinfarctions were excluded by analyses. The data have been analysed by chronograms and by means of "single cosinor" method, both for total cases, and for each subgroup of AMI. The results show a diurnal variation in AMI occurrence regarding the whole group, with a peak from 4:00 am to noon and with a secondary small no-significant peak in the late evening, and the minimum in the afternoon. Rhythmometric analysis demonstrates a significant circadian rhythm (p less than 0.001) with acrophase at 7:52 am (from 6:08 am to 9:36 am). A statistically-significant circadian rhythm is demonstrated in each subgroup, except in hypertensive patients. Acrophases of males and females, and of patients aged over or under 60 years do not differ from that of the whole group, and between them (p greater than 0.05). The peak of non Q wave AMI occurs at 4:44 am, while the peak of Q wave AMI at 10:08 am: this difference is significant (p less than 0.001). There is also a significant difference between the acrophases of AMI in the treated and untreated groups (p less than 0.01), as well as between normotensive and hypertensive subjects (p less than 0.001). The previous treatment seems able to anticipate the maximum occurrence of AMI in the whole group and in the group of Q wave AMI. These results are very similar to previous observations and confirm the greater morning occurrence of AMI. The present data are discussed in respect with the literature observations, and the possible pathophysiological mechanisms that contribute and conditionate the morning increase and the different peaks in subgroups of AMI patients are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)