Heart symbol
This article is part of a series.
Physical examination
Imaging techniques
Stress testing
Tilt testing
Cardiac catherization
Cardiac arrhythmias
Congenital heart disease
Endocardial disease
Heart failure
Ischaemic heart disease
Pericardial diasease
Valvular heart disease
Vascular disease
Cardiology portal

An electrocardiogram (ECG or EKG) is a noninvasive procedure used to investigate the electrical activity of the heart.

Reading an ECGEdit

Rate and rhythm Normal resting heart rate is between 60 and 100 s. Below 60 s suggests bradycardia, above 100 s is tachycardia.
Axis 4 .
P waves Amplitude is normally less than 0.2mV (2mm), with a duration of < 0.12 s. Broad, bifid P waves indicate left ventricular hypertrophy.
PR interval Normally between 0.12 and 0.2 s. A short PR interval can occur in the presence of an acessory pathway.
QRS duration Normally less than 0.2 s duration. Broad QRS complexes denote a delay in conduction through the bundle brances.
QRS amplitude Affected by ventricular muscle mass Patients with left ventricular hypertrophy have large QRS complexes.
ST segment Measured with reference to ECG baseline. ST segment elevation occurs in acute MI, left ventricular aneurysm, pericarditis and Prinzmetal's angina. Occaisionally occurs with severe hyperkalaemia, hypothermia, pulmonary embolism and stroke. Normal finding in some individuals.
ST segment depression occurs in cardiomyopathy, infiltrative cardiac disease, myocardial ischaemia and infarction and with many drugs and metabolic disturbances.
QT interval QT interval reflects duration of ventricular repolarisation. Varies with heart rate so calculate empirical corrected interval (QTC), Bazzett's formula. Normally between 0.38 and 0.46 s.
T and U waves T waves are normally upright in all leads except aVR and V1. Isolated T wave inversion in lead III may be normal. T wave inversion is a common abnormality. It is caused by the pathologies that cause ST segment depression and many additional conditions, e.g. hyperventilation, exercise, stroke and allergic reactions.