New method for measuring QRS duration using high-frequency electrocardiography.

Definition of QRS onset and offset is a basic problem in electrocardiography. Current techniques rely either on subjective estimates or on computer algorithms using QRS derivative or spatial vector velocity parameters. We developed a spectral method based on the observation that the QRS complex, unlike the P wave, PR segment, or ST-T complex is comprised of significant frequencies greater than 50 Hz. Accordingly, we adapted a microprocessor-based electrocardiograph (ECG) system with a signal-averaging program to reduce noise and a 50-300 Hz digital filter. Leads I and aVF were simultaneously acquired by computer in 40 subjects with a wide range of QRS duration (55.5-161 ms). Excellent correlation (r = 0.98) was noted between high-frequency QRS duration measurement and careful visual determinations made at high gain and expanded time scale. The high-frequency ECG appears to provide an objective physiological definition of the QRS complex based on spectral content not on morphology or slope.