High frequency QRS electrocardiography in the detection of reperfusion following thrombolytic therapy

The hypothesis that an increase in the amplitude (root-mean-square voltage) of the high frequency (150-250 Hz) components of the QRS complex occurs with successful reperfusion following thrombolytic therapy in acute myocardial infarction (AMI) and fails to occur when thrombolysis fails was tested. Clinical markers for successful or failed reperfusion following thrombolytic therapy for AMI are notoriously insensitive. The amplitude of the high-frequency components of the QRS complex decreases during ischemia and returns to normal with resolution of ischemia, but neither the variability in measurement of these potentials nor their patterns of change during the course of AMI have been described. In 32 control subjects, the average coefficient of variation for the amplitude of the highfrequency QRS complex was 10% or 0.3 uV. Based on these data, for the acute infarction population a significant change in this measurement was therefore defined as a change in amplitude > 20% or 0.6 uV on two consecutive recordings. In 30 patients with AMI treated with a thrombolytic agent, either cardiac catheterization, serial serum myoglobin, or complete resolution of ST-segment elevation were used to define successful or failed reperfusion. High-frequency QRS electrocardiograms were obtained at the start of treatment with a thrombolytic agent and for 3 h thereafter using a signal-averaging technique and digital filtering. Standard 12-lead electrocardiograms were obtained at the same time. In patients who reperfused successfully, the high-frequency QRS amplitude increased significantly (1.2 ± 0.9 uV above its nadir at 83 ± 36 min after initiation of thrombolytic therapy) in 23 of 25 patients. In contrast, the highfrequency QRS amplitude did not change or declined in all five patients who failed to reperfuse (-0.4 ± 0.4 uV, p < 0.05 compared with successful reperfusion). Traditional clinical markers such as resolution of chest pain and ST-segment elevation failed to distinguish successful and failed reperfusion. High-frequency QRS electrocardiography is a rapid, reliable bedside technique for discriminating between successful and failed reperfusion in patients treated with thrombolytic agents for AMI.