Introduction

Cardiac contraction is associated with electricity, discovered by Italian physicist Carlo Matteucci in 1842, subsequently captured as a tracing in 1878 by British physiologists John Burdon Sanderson and Frederick Page, using a ‘capillary electrometer’ on frog hearts. Less than a decade later, Augustus Waller at St Mary's Medical School, London, demonstrated in humans that each heartbeat was preceded by electrical activity. Willem Einthoven, now recognised as the inventor of the Electrocardiograph, was present at his lecture, and frustrated by limitations of the capillary electrometer, he developed the ‘string galvanometer’ which could record miniscule deflections in current. In 1895, he published drawings of the heart's deflections, which he termed P, Q, R, S and T.1 The first paediatric ECG was recorded in 1908, and it was soon recognised that age-related changes in anatomy and physiology impact on the normal electrocardiographic features.2

The purpose of this article is to not to provide the reader with skills to become an expert in paediatric ECG interpretation: the basics are assumed. Rather, the aim is to review basic physiology and technology and to address the value of the ECG in three general paediatric clinical scenarios.

Physiology

During the normal cardiac cycle, electricity is produced by ions moving across myocyte membranes, changing the membrane potential from negative to positive and back again (the action potential). The ECG records this electrical activity via the skin surface. Detailed physiology can be found elsewhere,3 but box 1 provides some salient reminders about the heart's electricity in relation to the ECG.