50Hz interference and noise in ECG recordings--a review

In this review paper, a simplified model is used to explain the various ways by which 50Hz interference can disturb electrocardiogram recordings. From the model, noise expressions are also derived which explain sources of noise in recordings. Means of minimising the 50Hz interference and noise with emphasis placed on skin abrasion and right-leg drive circuits are discussed. An add-on circuit which can be used with existing amplifiers to improve their performance is shown. Previous interference analysis has concentrated on 2-input differential amplifiers, however in modern hospitals, a wide variety of amplifier configurations are used. An example is the Wilson Central Terminal which is used to obtain a zero potential in body surface mapping applications. In this review it is shown with an example for an ECG amplifier incorporating a Wilson Central Terminal, how it is easy to extend the interference model to other applications.