Cardiology | |
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This article is part of a series. | |
Investigations | |
Physical examination Electrocardiography Imaging techniques Stress testing Tilt testing Cardiac catherization | |
Conditions | |
Cardiac arrhythmias Congenital heart disease Endocardial disease Heart failure Ischaemic heart disease Pericardial diasease Valvular heart disease Vascular disease | |
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An electrocardiogram (ECG or EKG) is a noninvasive procedure used to investigate the electrical activity of the heart.
Reading an ECG[]
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. |