Decrease in the high frequency QRS components depending on the local conduction delay

The high frequency components contained in the QRS complex (HF-QRS) are a powerful indicator for the risk of sudden cardiac death. However, it is controversial whether conduction delay increases or decreases the HF-QRS. In 21 anesthetized, open-chest dogs, the right atrium was constantly paced. A cannula was inserted into the left anterior descending artery and flecainide, lidocaine or disopyramide was infused to slow the local conduction. Sixty unipolar electrograms were recorded from the entire ventricular surface and were signal-averaged. Data were filtered (30-250 Hz) by using fast-Fourier transform. The HF-QRS was calculated by integrating the filtered QRS signal. Activation time (AT; dV/dt minimum) was delayed and the HF-QRS was reduced in the area perfused by flecainide, lidocaine or disopyramide. The percent increase in AT closely correlated the percentage decrease in the HF-QRS; the correlation coefficients were 0.75, 0.83 and 0.76 for flecainide, lidocaine and disopyramide infusion, respectively, (p<0.001). Decrease in the HF-QRS linearly correlated with the local conduction delay. This study proved that conduction delay decreases the HF-QRS, and that the HF-QRS is a potent indicator of disturbed local conduction.