Objective—To evaluate laboratory markers of defibrination early after thrombolytic therapy and to determine their relation to residual stenosis and left ventricular ejection fraction measured angiographically before discharge from hospital.
Design—Prospective analysis of defibrination after streptokinase measured by fibrinogen assay and thrombin time to provide a comparison of these coagulation variables for predicting angiographic responses to treatment in patients with acute myocardial infarction.
Setting—The coronary care unit of a district general hospital.
Patients—44 patients with acute myocardial infarction treated by streptokinase infusion, all of whom underwent paired blood sampling before and one hour after streptokinase and cardiac catheterisation at a median of six (interquartile range 3–9) days later.
Main outcome measures—Assay of thrombin time and plasma fibrinogen concentrations one hour after streptokinase infusion. Relations between these coagulation variables and residual stenosis in the infarct related coronary artery and left ventricular ejection fraction. Separate analyses are presented for all patients (n = 44) and those with patency of the infarct related artery (n = 35).
Results—Streptokinase infusion produced profound defibrination in every patient as shown by changes in thrombin time and circulating fibrinogen. Thrombin time after streptokinase infusion correlated significantly with both residual stenosis (r = −0·43, p < 0·005) and left ventricular ejection fraction (r = 0·38, p < 0·02). The importance of these correlations was emphasised by the interquartile group comparison which showed that a thrombin time ≥49 seconds predicted a residual stenosis of 74% and an ejection fraction of 65%, compared with 90% and 49% for a thrombin time ≤31 seconds (p < 0·01). When the analysis was restricted to patients with patency of the infarct related artery, the correlation between thrombin time and residual stenosis remained significant and group comparisons continued to show that patients in the highest quartile range had more widely patent arteries and better preservation of ejection fraction. Analysis of the fibrinogen data, on the other hand, showed insignificant or only marginally significant correlations with these angiographic variables.
Conclusions—Early after streptokinase infusion for acute myocardial infarction, the level of defibrination measured by thrombin time has an important influence on residual coronary stenosis and left ventricular ejection fraction at discharge from hospital, values above 49 seconds being associated with the best angiographic result.
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