Mohammad Sohail, Abdul Rehman Abid, Muhammad Azhar.
Circadian variations in the onset of acute myocardial infarction.
J Cardiovascular Dis Jan ;10(3):73-8.

Objective: To determine whether the circadian onset of acute myocardial infarction (AMI) varied by sex, age, cardiovascular risk factor. Materials and methods: This Cross sectional survey was conducted at the Cardiology Department, Punjab Institute of Cardiology, Lahore from February to July 2010. After fulfilling the inclusion criteria 560 patients presenting with new onset acute myocardial infarction were studied. An informed consent was taken from them for using their personal data record for the study. All patients were treated according to standard management protocol of the hospital and the study did not involve any additional risk to the patients. Demographic information including name, age, and sex were obtained. The study patients were divided into 4 groups according to time of onset of symptoms. Group I comprised of patients presenting with onset of symptoms between 0-6 hours, Group II, 6:01-12 hours, Group III 12:01-18 hours and Group IV 18:01-24 hours. Cardiovascular risk factors were compared between the groups by applying Chi Square test. Results: Two peaks of onset of symptoms were observed, first during 6:01-12 hours 181(32.3%) patients and the second between 12:01-18 hours 152(27.1%) patients. A significant association was observed in time of onset of acute myocardial infarction. The trough was evening time 18-24 hours when only 92(16.5%) patients had acute MI. It was observed that patients presented 2.0 times more during the morning 6:00-12:00 hours as compared to evening 18:00-24:00 hours. Mean age of the study population was 55.1±12.3 years. Mean age was similar in all the four groups p<0.05. There were 450(80.4%) males and 110(19.6%) females p<0.01. A non-significant association was observed in time of onset of acute myocardial infarction among Diabetics p<0.351and hypertensives p< 0.432 in all four groups. Significant association among smokers was noted p<0.006. Patients presenting during the morning hours 6:00-12:00 were treated more aggressively as 133(73.5%) patients in Group II received streptokinase infusion for pharmacologic thrombolysis compared to 83(61.5%) in Group I and 96(63.2%) in Group III and 57(62.0%) in Group IV received streptokinase infusion p<0.074. A total of 135(24.1%) had arrhythmia in post MI phase. The occurrence of Heart failure was highest in Group II 54(29.8%) and lowest in Group IV 22(23.9%) with p<0.531. A total of 66 (11.8%) mortalities recorded during the study period among the 560 patients p<0.140. Conclusion: The onset time of AMI has bimodal appearance with an early peak at 6-12:00 hours and a second lesser peak was seen during the period between 12:00-18:00 hours. Patients with diabetes mellitus and hypertension did not show any significant peaks as the time of onset of acute myocardial infarction.

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