Short answers, pulled from the story.
An electrocardiogram is a line graph of the heart's electrical activity recorded over time, typically ten seconds, using electrodes placed on the skin. It shows voltage versus time across multiple perspectives called leads, and is used to detect arrhythmias, heart attacks, and other cardiac conditions.
Willem Einthoven built the first practical electrocardiograph in 1901 using a string galvanometer while working in Leiden, the Netherlands. He received the Nobel Prize in Medicine in 1924 for this work. The string galvanometer itself was invented by French engineer Clement Ader in 1897.
A standard 12-lead ECG uses ten electrodes placed on the limbs and chest to produce twelve leads, each recording the heart's electrical activity from a different angle. Four electrodes are placed on the limbs and six are placed across the chest in standardized anatomical positions.
The P wave represents depolarization of the atria and should last less than 80 milliseconds. The QRS complex represents depolarization of the ventricles and normally runs 80-100 milliseconds. The T wave represents repolarization of the ventricles and typically lasts around 160 milliseconds.
Yes. The fourth-generation Apple Watch released in 2018 and the Samsung Galaxy Watch 4 released in 2021 are capable of recording an ECG signal. These devices typically use only two electrodes and deliver a single lead I recording, compared to the ten electrodes of a clinical 12-lead ECG.
The Holter monitor is a portable device that records continuous ECG signals and was introduced in 1962. It enables detection of arrhythmias that would be missed by a standard ten-second ECG. Its development later led to the implantable loop recorder, a subcutaneous device with batteries that last for years.