Effects of 60-Hertz notch filtering on local abnormal ventricular activities

It is known that electrical signals can be affected by notch filtering.

We sought to investigate the effect of 60-Hz notch filtering on local abnormal ventricular activities (LAVA) in patients undergoing ventricular tachycardia ablation.

To ensure catheter stability, only patients undergoing ablation using Stereotaxis mapping catheters were enrolled. Catheter stability was judged by the display on the electroanatomic map and the morphology of the bipolar and unipolar electrograms of the ablation catheter. At sites recording stable LAVA, 60-Hz notch filtering was applied. The duration, amplitude, and morphology of LAVA were compared before and after filtering. The area under LAVA was used to analyze the amplitude of continuous LAVA.

A total of 110 LAVA potentials recorded from 13 patients were analyzed. Notch filtering significantly affected the LAVA morphology and reduced their amplitude (the sum of the absolute value of the largest positive and negative voltages before filtering: 0.267 mV [0.191-0.395 mV]; after filtering: 0.172 mV [0.112-0.266 mV]; P < .001). At least 2 high-frequency components were introduced into the LAVA by filtering at 33 sites. The area under continuous LAVA was reduced by 28% from 24.64 cm² (16.20-33.45 cm²) to 17.53 cm² (10.52-23.82 cm²) (P < .001). The duration of continuous LAVA was reduced by 12% from 79.2 ms (55.0-93.0 ms) to 69.5 ms (53.0-88.5 ms) (P < .001).

Notch filtering can distort LAVA by reducing their amplitude, changing their morphology, and shortening their duration, leading to potential false positives and negatives. Mitigating the 60-Hz noise should focus on eliminating the source of noise, not applying notch filtering.