The effect of condensers in the electrocardiograph

Abstract

1. 1. Condensers placed in the string galvanometer or amplifier type of electrocardiography make compensation for “skin current” automatic. String galvanometers are not ordinarily equipped with condensers; whereas most amplifier electrocardiographs are so equipped. 2. 2. The presence of condensers introduces distortion. 3. 3. The chief distortions that may be introduced by condensers in the electrocardiograph in clinical practice are RS-T deviation and diminution in the height of the R-wave. Since attention is paid to the RS-T segment in the diagnosis of coronary artery disease, rheumatic fever, etc., its deviation is significant. The time relationships are unaltered. 4. 4. The magnitude of the distortion is proportional to the duration and amplitude of the wave being recorded and is also, in a simple circuit (string galvanometer), inversely proportional to the product of the esistance and capacity. 5. 5. This product is known as the time constant. An amplifier circuit (which is a series of simple circuits) has an equivalent time constant to which the distortion is likewise inversely proportional. A simple method is given for determining this constant. 6. 6. Formulas are given for determining the magnitude of the distortion. 7. 7. If the time constant of the circuit is 2.0 seconds or more, the distortion is not usually significant in clinical practice.