Simulation of anteroseptal myocardial infarction by electrocardiographic filters

Abstract

Background Most electrocardiographs have high-pass filters that may be used to attenuate baseline wander due to respiratory artifact. However, the T wave also has low-frequency components and may be distorted by these filters. Our aim was to investigate the effect of high-pass filters on the ST segment. Methods Twenty healthy volunteers had a standard 12-lead electrocardiogram recorded using a Bard EP Labsystem (Bard Inc, Lowell, Mass) at different high-pass filter settings (0.05, 0.1, 0.5, and 1.0 Hz). ST-segment elevation or depression was measured using digital calipers at each setting and the electrocardiogram classified as being either normal or suggestive of myocardial infarction. Results There were no significant differences in ST elevation between 0.05- and 0.1-Hz filter settings. However, at 0.5 and 1.0 Hz, there was significant ST elevation in the right precordial leads and ST depression in the inferior leads. The greatest changes were observed in V 2, with an ST elevation of 0.13 ± 0.08 and 0.18 ± 0.09 mV at 0.5 and 1.0 Hz, respectively ( P < .0001 compared with 0.05 Hz). All tracings were considered normal at 0.05- and 0.1-Hz filter settings. However, at 0.5 and 1.0 Hz, 60% and 100%, respectively, of tracings were suggestive of anteroseptal myocardial infarction. Signal distortion was attributed to phase nonlinearities of the filters. Conclusions High-pass filters may distort the ST segment and simulate anteroseptal myocardial infarction. These filters should comply with current standards if used on electrocardiographs and be used with caution. In case of doubt, the tracings should be compared with minimally filtered recordings.