This is a 55 yo male with chest pain. The medics recorded the first ECG, which shows unequivocal ST elevation in leads V4-V6.
Our medics have the authority to activate the cath lab from the field, and they did so. After arrival in the ED, the second ECG was recorded.
There is no significant ST elevation here. It has resolved spontaneously. There is ST depression with hyperacute T waves, best seen in lead V3. This has been associated with 3% of LAD occlusion (http://content.nejm.org/cgi/content/extract/359/19/2071).
The patient had LAD occlusion; because of the prehospital ECG, and the authority to activate the cath lab, his door to balloon time was 36 minutes. Had there been no prehospital ECG, there may have been no coronary intervention at all because of the absence of ST elevation in the ED.