Short answers, pulled from the story.
Alexander Muirhead attached wires to a patient with fever to obtain an electronic record of their heartbeat in 1872. This early attempt laid the groundwork for future discoveries in cardiac monitoring.
Willem Einthoven received the Nobel Prize in Medicine in 1924 for his pioneering work using the string galvanometer. He revolutionized the field when he used this device in 1901 while working in Leiden, the Netherlands.
The three main components to an ECG are the P wave which represents depolarization of the atria, the QRS complex representing depolarization of the ventricles, and the T wave showing repolarization of the ventricles. These components form the theoretical waveform created by Einthoven.
Electrode V1 sits in the fourth intercostal space just to the right of the sternum. The precordial electrodes lie in the transverse horizontal plane perpendicular to the other six leads.
Portable devices have existed since the Holter monitor was introduced in 1962. Traditional monitors use electrodes with patches on the skin to record the ECG but new devices can stick to the chest as a single patch without need for wires.