After reading this chapter you should be able to:

draw, label and scale a typical ECG trace, stating the chosen lead (5.1–5.3);

state the origin of the P, QRS and T waves, and the PR and ST intervals (5.2);

explain what a cardiac dipole is (5.4);

sketch out how the cardiac dipole changes with time in the frontal plane during ventricular depolarization (5.5);

explain why different leads record different QRS patterns during the same systole (5.6);

outline the ECG changes caused by ischaemic heart disease (5.9);

state the roles of triggers and substrate in initiating and maintaining arrhythmias (5.10, 3.11);

give the meaning, mechanism and significance of:

heart block;

sinus arrhythmia;

ectopic beat;

atrial tachycardia;

atrioventricular nodal re-entrant tachycardia;

atrioventricular re-entrant tachycardia;

atrial flutter;

atrial fibrillation;

ventricular tachycardia;

ventricular fibrillation.