The electrocardiogram (ECG), introduced into clinical practice more than 100 years ago by Einthoven, constitutes a lineal recording of the heart’s electrical activity that occurs successively over time. An atrial depolarisation wave (P wave), a ventricular depolarisation wave (QRS complex) and a ventricular repolarisation wave (T wave) are successively recorded for each cardiac cycle (Figures 1A–C). As these different waves are recorded from different sites (leads) the morphology varies (Figure 2).Nevertheless, the sequence is always P–QRS–T. An ECG curve recorded from an electrode facing the left ventricle is shown in Figure 1D. Depending on the heart rate, the interval between waves of one cycle and another is variable
