Description
Electrocardiographs (ECGs) are medical instruments used to measure the rhythm at which the heart contracts and the relative strength of different parts of the heart muscle. Electrical impulses in the heart are created at the sinoatrial node – a ‘pacemaker’ tissue in the right atrium – and travel to the heart muscle. On receiving this impulse, a contraction of the muscle fibres is induced and blood is pumped. Electrodes placed on the skin of a patient measure the voltage at different sides of the heart muscle and the ECG subsequently measures the difference in voltage between pairs of electrodes. The product of these measurements is a cardiogram – a record that displays an interpretation of the electrical activity of the heart over time. ECG’s are particularly useful for the diagnosis of irregular heartbeat rhythms caused by damage to the conductive tissue in the heart or by an inadequacy or abundance of electrolytes, such as Potassium and other dissolved salts. However, it is not capable of measuring all aspects of muscle activity in the heart and is ineffective in measuring pumping ability in comparison to echocardiographic methods.

Although technologies that recorded electrical traces of the heartbeat had been developed at the end of the nineteenth-century, Willem Eithoven’s String Galvanometer was found to be capable of more sensitive measurements than its predecessors. Eithoven characterised several ECG measurements, described electrocardiographic features of several cardiovascular disorders, and was later awarded the Nobel Prize in Medicine for his discovery.

The Cambridge Scientific Instrument Company developed their first ECG in 1912 based on Eithoven’s design. However, the instrument covered a floor space of 6ft by 3ft and weighed 336lb. It was far from portable and one of the most astonishing elements of the history of the ECG is the shift from a cumbersome piece of equipment used by the hospital specialist to the portable instrument of the general clinician. The CSI manufactured its first ECG with a valve amplifier in 1952. Named the ‘Electrite’, it had a heated stylus that recorded heart activity on wax paper by evaporating wax on the recording paper to reveal a dark line where the hot stylus had travelled, thus tracing its movement. However an instrument that utilised the same heated stylus, but replaced the valve with a transistor-based amplifier, superseded the ‘Electrite’ and was dubbed the ‘Transrite’. This particular ECG was produced in England in 1957 and, at some point, belonged to the War Memorial Hospital in Scunthorpe, Lincolnshire.
18/09/2009
Created by: M.A. Coxhead on 18/09/2009