Role of the Historical Electrocardiogram in Identifying Acute Coronary Syndrome

Sensitivity (SE) and specificity (SP) for diagnosing acute coronary syndrome in prehospital ECGs is insufficient. The guidelines state that comparison of prehospital ECGs and a previous ECG tracing is valuable, particularly in case of pre-existing ECG abnormalities. Our study investigates the additional value of the historical ECG in detecting ischemia in prehospital phase. Data belong to the SUBTRACT study, which includes couples of 10-second 12-lead prehospital and historical ECGs from 1182 patients. Retrospective evaluation of the prehospital ECGs yielded 169 patients with, and 1013 patients without ischemia in prehospital ECG. Overall, each ECG couple were characterized by 47 features, which were grouped in the first set, including 18 direct measurements from the prehospital ECG, and the second set, including the first set and 29 serial prehospital-historical ECG differences. The sets were used to create two dendrograms, that divided the data into two clusters. Clusters were labeled as ischemia cluster (i.e., including over 50% of the ischemia patients) and non-ischemia cluster, and evaluated by SE and SP. Metrics of the second dendrogram (SE=71%; SP=69%) are higher than those of the first dendrogram (SE=22%; SP=57%). We conclude that serial differences improve ischemia identification in the ambulance, thus proving the additional diagnostic value of a historical ECG.