ACUTE MYOCARDIAL INFARCTION;

SIGNIFICANCE OF 1st SET OF CK-MB IN DIAGNOSIS

Abstract

^{Objective: To assess the reliability of the first set of CK-MB in establishing diagnosis of acute myocardial infarction in different subgroups of the patients according to their time of presentation after symptom onset. Material a n d m e t h o d s : Prospective observational study was carried out in Armed Forces Institute of Cardiology/National Institute of Heart Diseases (AFIC/NIHD) Rawalpindi, from April to September 2005. We studied 300 consecutive cases presenting with typical electrocardiographic changes of acute ST Elevation Myocardial Infarction to the Emergency & Reception department of AFIC/NIHD (confirmed later on as acute STEMI with raised serial serum cardiac enzymes levels). We documented values of CK-MB at the time of presentation in different subgroups of the patients according to duration of symptom onset. R e s u l t s : This study was predominantly male dominated (approximately 78%), with a mean age of 58 +11 years. Majority of patients i.e.216 (72%) presented within first 6 hours of onset of symptoms, 60 (20%) within 6-12 hrs, 6 (2%) within 12-24 hrs and 18 (6%) after 24 hrs of onset of symptoms. Overall serum cardiac enzymes sent at the time of presentation revealed that 126 (42%) patients had normal CK-MB (<24U/L) and another 66 (22%) had a minimal rise in CK-MB (25-49 U/L). Only 108 (36%) patients 3 had serum CK-MB
levels more than double the normal value. Amongst the patients presenting within the first 6 hours of onset of symptoms, 104 (48%) had normal CK-MB values, 48 (22%) had a minimal rise (<49 U/L) and only 64 (30%) had a significant rise in CK-MB levels i.e. more than double the normal values or more than 5% of CK value. Out of 60 patients who presented within 6-12 hours of onset of symptoms, 54(90%) had more than double the normal value of CK-MB and 6(10%) had mild rise in CK-MB. All the patients (100%) who presented within 12-24 hours of onset of symptoms i.e. 6(2%) and more than 24 hours 18(6%) had significant rise in CK-MB. C o n c l u s i o n : This study shows that the first set of CK-MB alone has very little value in diagnosing acute myocardial infarction especially in the patients who presented within 6 hours of onset of symptoms. Reliability of CK-MB in diagnosing acute myocardial infarction greatly improves to the maximum in those patients who present more than six hours after symptom onset.}