Electrocardiogram (ECG) and monitoring Continuous 12-lead ST-monitoring is initiated on scene by use of a commercial monitor-defibrillator (LIFEPAK 12, Medtronic Emergency Response Systems, USA), and continued during transport to the local hospital (if not bypassed) and during transfer to the interventional hospital. On arrival at the interventional hospital traditional ECG electrodes are replaced by radiolucent carbon fiber lead wire electrodes (Ambu Blue Sensor QR electrodes, Ambu A/S, Denmark) enabling ST-monitoring to be continued during and 90 minutes following PCI. The analog ECG signals sampled by the system are digitized at a sample rate of 500 Hz for processing by the GE/Marquette Medical Systems 12SL ECG interpretive algorithm. At 30-second interval the ST-monitoring program generates a median QRST-complex for all 12 leads based on a 10-second epoch of ECG data. From each of these median QRST-complexes the program estimates the ST-deviation at the STM point, halfway between the J-point of the QRS complex and the start of the T-wave. If a 0.1 mV change in ST-deviation lasts for 2.5 minutes then the software automatically acquires and stores a 10-second 12-lead ECG waveform. All 12-lead ECG waveforms and continuous ST-monitoring data are transferred to a personal computer and stored by a random key for subsequent blinded analysis at the Core Lab. at Skejby Sygehus.