Electrocardiographic evaluation of reperfusion therapy in patients with acute myocardial infarction

P Clemmensen
Danish Medical Bulletin 1996, 43 (1): 68-85
The present thesis is based on 6 previously published clinical studies in patients with AMI. Thrombolytic therapy for patients with AMI improves early infarct coronary artery patency, limits AMI size, improves left ventricular function and survival, as demonstrated in large placebo-controlled clinical trials. With the advent of interventions aimed at limiting AMI size it became important to assess the amount of ischemic myocardium in the early phase of AMI, and to develop noninvasive methods for evaluation of these therapies. The aims of the present studies were to develop such methods. The studies have included 267 patients with AMI admitted up to 12 hours after onset of symptoms. All included patients had acute ECG ST-segment changes indicating subepicardial ischemia, and patients with bundle branch block were excluded. Serial ECG's were analyzed with quantitative ST-segment measurements in the acute phase and compared to the Selvester QRS score estimated final AMI size. These ECG indices were compared to and validated through comparisons with other independent noninvasive and invasive methods, used for the purpose of evaluating patients with AMI treated with thrombolytic therapy. It was found that in patients with first AMI not treated with reperfusion therapies the QRS score estimated final AMI size can be predicted from the acute ST-segment elevation. Based on the number of ECG leads with ST-segment elevation and its summated magnitude, formulas were developed to provide an "ST score" for estimating the amount of myocardium in jeopardy during the early phase of AMI. The ST-segment deviation present in the ECG in patients with documented occlusion of the infarct related coronary artery, was subsequently shown to correlate with the degree of regional and global left ventricular dysfunction. Because serial changes in ST-segment elevation, during the acute phase of AMI were believed to reflect changes is myocardial ischemia and thus possibly infarct artery patency status, the summated ST-segment elevation present on the admission ECG was compared to that present after administration of intravenous thrombolytic therapy, and immediately prior to angiographic visualization of the infarct related coronary artery. The entire spectrum of sensitivities and specificities, derived from different cut-off values for the degree of ST-segment normalization, was described for the first time. It was found that a 20% decrease in ST-segment elevation could predict coronary artery patency with a high level of accuracy: positive predictive value = 88% and negative predictive value = 80%.(ABSTRACT TRUNCATED)

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