Acute myocardial infarction; significance of 1 [st] set of CK-MB in diagnosis

ABSTRACT

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. 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 of the Emergency and 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. 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 [25-49U/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. 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