The Electrocardiogram (ECG) – The Electrical Activity of the Heart

Bioelectricity is about the electrical phenomena of life processes, and is a parallel to the subject electrophysiology. The numerous elegant and ingenious experimental studies of many investigators, provided insights into electrophysiological activity. It emerged that several functions of life could be explained by bioelectricity. The electrocardiogram reflects the electrical events that controls the heart function. The heart exhibits an electrical system that includes the sinoatrial node, the atrioventricular node, the bundle of His, the right and left branches and the Purkinje fibres. This cardiac electrical system not only controls the rhythmical contractions of the heart, but also coordinates and ensures that atria and ventricles contract at the right time in order to maximise the efficiency in pumping blood.

The electrocardiogram, commonly known as ECG or EKG, was invented by the Dutch scientist Willem Einthoven in 1903, and received the Nobel Prize in medicine in 1924. Each heartbeat results from an electrical current that causes the heart to contract, such electrical current spreads over the surrounding tissues, and a small amount reaches the surface of the body (the skin). The ECG is a recording of that electrical activity. During an ECG recording an array of skin electrodes are placed in the chest and limbs of a person, and as the heart undergoes depolarisation and repolarisation during each heartbeat, it generates a low voltage current, which is detected by the electrodes and recorded by an external device, called electrocardiograph. The ECG is composed of different waves corresponding to the spreading of the electrical current throughout the heart. The relative timing, size and direction of these waves provide information about the heart rate, the heart rhythm and health. The ECG is used in medicine for diagnosing a number of heart conditions, such as cardiac arrhythmias acute or prior to myocardial infarction, cardiac hypertrophy, as well as determine if bradycardia is physiological or is caused by heart block. Furthermore, the ECG is used during an exercise stress test, in which the patient performs a standardised exercise protocol to assess the presence of coronary heart diseases, and blood supply to the heart.

Heart problems may result in altered heart rhythm. Generally in these cases the heart beats too slowly and the volume of blood pumped is insufficient to meet the metabolic demand. Implantable cardiac pacemakers are devices that control the heart rhythm, and have allowed millions of people to return to normal life. The Cardiac pacemaker is just an example demonstrating how bioelectronic devices play a key role in medicine.