Electrocardiogram, white blood cell count, and erythrocyte sedimentation rate

An electrocardiogram (ECG) is the most useful direct test available. Approximately 50% of acute MIs show unequivocal changes on the first ECG. Another 30% have abnormalities that might be due to acute infarct but that are not diagnostic, because the more specific changes are masked or obscured by certain major conduction irregularities such as bundle-branch block or by previous digitalis therapy. About 20% do not show significant ECG changes, and this occasionally happens even in patients who otherwise have a typical clinical and laboratory picture. Ordinary general laboratory tests cannot be used to diagnose acute infarction, although certain tests affected by tissue damage give abnormal results in the majority of patients. In classic cases a polymorphonuclear leukocytosis in the range of 10,000-20,000/mm3 (10-20 Ч 109 /L) begins 12-24 hours after onset of symptoms. Leukocytosis generally lasts between 1 and 2 weeks, depending on the extent of tissue necrosis. Leukocytosis is accompanied by a moderately elevated temperature and an increased erythrocyte sedimentation rate (ESR). The ESR abnormality persists longer than the leukocytosis, remaining elevated sometimes as long as 3-4 weeks.