Methods for Recording Electrocardiograms
Sometimes the electrical currents generated by the cardiac muscle during each beat of the heart change electrical potentials and polarities on the respective sides of the heart in less than 0.01 second. Therefore, it is essential that any apparatus for recording electro-cardiograms be capable of responding rapidly to these changes in potentials.
Many modern clinical electrocardiographs use com-puter-based systems and electronic display, while others use a direct pen recorder that writes the elec-trocardiogram with a pen directly on a moving sheet of paper. Sometimes the pen is a thin tube connected at one end to an inkwell, and its recording end is con-nected to a powerful electromagnet system that is capable of moving the pen back and forth at high speed. As the paper moves forward, the pen records the electrocardiogram.The movement of the pen is con-trolled by appropriate electronic amplifiers connected to electrocardiographic electrodes on the patient.
Other pen recording systems use special paper that does not require ink in the recording stylus. One such paper turns black when it is exposed to heat; the stylus itself is made very hot by electrical current flowing through its tip. Another type turns black when electri-cal current flows from the tip of the stylus through the paper to an electrode at its back. This leaves a black line on the paper where the stylus touches.
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