Original Article Nepal Medical College Journal 2007; 9(1): Changing chronobiology of cardiovascular outcome following prophylaxis Vinu Mulavarickal Jose, 1 Navneet Sharma, 2 Debasish Hota 1 and Promila Pandhi 1 1 Department of Pharmacology and 2 Department of Internal Medicine, PGIMER, Chandigarh 160012 India Corresponding author: Hota D, DM Clinical Pharmacology, Assistant Professor in Clinical Pharmacology, PGIMER, Chandigarh 160 012 India. e-mail: vishnujose@hotmail.com ABSTRACT Cardiovascular events like angina, myocardial infarction and stroke have shown an increasing occurrence in the morning hours. We did this pilot nested case control study to see for any change in the time pattern of occurrence of cardiovascular events among patients on prophylaxis. A pilot study was done and the demographic characters, history of cardiovascular diseases, time of occurrence of cardiovascular event, history of drug intake and compliance were noted. Eighty four patients on prophylaxis and 135 patients presenting for the first time reported during the study period. Age did not show any significant difference. More males were getting prophylaxis for stroke and for the combined cardiovascular events. Time distribution of events showed peak occurrence between 8 to12 hr followed by 20 to 24 hr among those who were not on prophylaxis and reverse in those on secondary prophylaxis. Odds of developing cardiovascular events though was not significantly different, was higher between 16-20 hr (1.26), 20-24hr (1.48) and 0-4 hr (1.22) among those on prophylaxis. Seventy eight patients were taking antihypertensives. This observation demands further studies to determine the cause of evening increase in cardiovascular event especially since very little is known regarding evening exaggeration of risk factors which is becoming relevant especially in those getting prophylaxis. Keywords: Chronobiology, cardiovascular outcome, prophylaxis. INTRODUCTION Studies have shown that cardiovascular events like angina, myocardial infarction and stroke are more common during the morning hours with a probable second peaking towards evening. 1-11 Patients who are on prophylaxis of these diseases are expected to have an altered pattern due to variation of the physiological parameters by drugs and life style modifications. Very few studies have been done with this objective and those studies have observed a blunting of morning peak of cardiovascular outcome. 1,12-18 Since we have observed a different pattern, we did this pilot study to compare the time of occurrence of cardiovascular events like myocardial infarction, angina and stroke among patients on prophylaxis with drugs with those who are not on prophylaxis. MATERIALS AND METHODS This was a pilot nested case control study conducted at the emergency department of an Indian tertiary care hospital from October 2004. Patients of either sex who reported to the emergency department with suggestive history, signs and symptoms, electrocardiograph evidence of angina or myocardial infarction and computerized tomography evidence of cerebrovascular disease were included in the study. Patients or their bystanders were interviewed regarding demographic characters, history of cardiovascular diseases, time of occurrence of cardiovascular event, history of drug intake and compliance. Exclusion criteria included patients who gave insufficient information and those taking medicines irregularly while those taking no drugs at all for the last week were considered as not on prophylaxis.