This article is part of a series.
| Physical examination |
| Cardiac arrhythmias |
Congenital heart disease
Ischaemic heart disease
Valvular heart disease
|v • d • e|
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.|
|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.|