The prognostic value of the prehospital electrocardiogram in ST elevation myocardial infarction patients treated according to the UMCG ambulance protocol

Background Treatment of ST elevation myocardial infarction (STEMI) is aimed at rapid restoration of perfusion. Changes occurring on the electrocardiogram (ECG) are related to perfusion. These changes are observed on ECGs before and after reperfusion therapy. However, little is known about the prognostic value of ECG changes occurring before coronary angiography. Therefore, we studied ECG changes on ECGs obtained by ambulance personnel. To our knowledge, no data on this subject exist. Our primary goal was to analyze which ECG parameter was the best electrocardiographic sign of early reperfusion. Furthermore, we correlated ECG parameters to enzymatic infarct size and we investigated if certain characteristics were predictive of improvement of the ECG before angiography. Methods and results We included 43 STEMI patients who were treated with medication in the ambulance and who were transferred directly to the catheterization laboratory. In the ambulance the first 12 lead ECG was made after arrival at the patient, the second after arrival at the catheterization laboratory. There were no significant differences in QRS duration or in the number of Q waves between the first and second ECG. Therefore only ST segment parameters were taken into account for statistical analysis. We observed that the sum of ST deviation on the second ECG was significantly higher in patients with TIMI flow 0-1 (no or low perfusion of the coronary artery) than in patients with TIMI flow 2-3 (partial or complete perfusion) before PCI (p = 0.006). Furthermore, the sum of ST deviation on the second ECG was independently related to enzymatic infarct size (p < 0.001). In patients with anterior infarction, ST resolution was significantly higher in patients with myocardial blush grade (MBG) 2-3 (moderate or normal myocardial flow) than in patients with MBG 0-1 (no or minimal myocardial flow) after PCI (p = 0.025). We also found that the sum of ST deviation on the first ECG was an independent predictor of rapid improvement of the ECG (ST resolution) (p = 0.02). Conclusion The present study has shown that the sum of ST segment deviation at arrival at the hospital is related to TIMI flow before PCI and enzymatic infarct size. ST segment resolution before intervention is related to MBG in patients with anterior infarction. ECG parameters are a useful marker of coronary perfusion and outcome and might be a surrogate endpoint for prehospital interventions. Larger studies have to confirm these pilot observations.