12 Facts About ECG

Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances .

Traditionally, "ECG" usually means a 12-lead ECG taken while lying down as discussed below.

Early ECG machines were constructed with analog electronics, where the signal drove a motor to print out the signal onto paper.

Many ECG machines are now portable and commonly include a screen, keyboard, and printer on a small wheeled cart.

Commonly, 10 electrodes attached to the body are used to form 12 ECG leads, with each lead measuring a specific electrical potential difference .

The 12-lead ECG has a total of three limb leads and three augmented limb leads arranged like spokes of a wheel in the coronal plane, and six precordial leads or chest leads that lie on the perpendicular transverse plane .

The former are typically used in a single ECG recording while the latter are for continuous recordings as they stick longer.

Each of the 12 ECG leads records the electrical activity of the heart from a different angle, and therefore align with different anatomical areas of the heart.

Interpretation of the ECG is fundamentally about understanding the electrical conduction system of the heart.

Ventricular fibrillation produces an ECG but is too dysfunctional to produce a life-sustaining cardiac output.

All of the waves on an ECG tracing and the intervals between them have a predictable time duration, a range of acceptable amplitudes, and a typical morphology.

ST elevation myocardial infarctions have different characteristic ECG findings based on the amount of time elapsed since the MI first occurred.