Glossary
A
- Aberration
{aberrancy, aberrant ventricular conduction} A reversible conduction abnormality resulting in wide QRS complexes with a bundle branch block appearance. - Accessory conduction pathway
An extra conduction pathway between the atria and ventricles. An accessory pathway may be seen on the EKG as a delta wave in Wolff Parkinson White syndrome. - Atrial fibrillation
{AF} The most common arrhythmia. The atria fibrillate at a frequency of 350-600 beats per minute. It is seen on the EKG as an oscillating, irregular baseline and the absence of p waves. See also the article atrial fibrillation. - Atrioventricular block
{AV blocks, heart blocks} A group of conduction blocks causing varying degree of impaired conduction between the atria and the ventricles of the heart. They are divided into first, second and third degree AV blocks. - Atrioventricular junction
{AV junction} The junction between the atria and the ventricles. The AV junction consists of the atrioventricular node and the bundle of His. See also the article electrical conduction system of the heart. - Atrioventricular node
{AV node} The electrical connection between the atria and the ventricles of the heart. It is located in the septum between the atria and capable of slowing down rapid atrial impulses, thus preventing rapid conduction to the ventricles (decremental conduction). See also the article electrical conduction system of the heart.
B
- Bifascicular block
The combination of right bundle branch block and block of either the left anterior fascicle or the left posterior fascicle of the left bundle branch. See also the article bifascicular block. - Bradycardia
A rhythm less than 60 beats per minute. - Bundle branch block
A conduction block of either the right or left bundle branch of the electrical conduction system of the heart. See also the article beat the bundle branch blocks. - Bundle of His
The part of the electrical conduction system originating from the AV node and ending in the bundle branches.
C
D
- Delta wave
A slurred, early upstroke of the QRS complex seen in Wolff Parkinson White (WPW) syndrome due to an accessory conduction pathway between the atria and ventricles.
E
- Electrocardiogram
{EKG, ECG} A recording of the electrical activity of the heart. Invented by Willem Einthoven, who in 1924 was awarded the Nobel Price in Medicine for the discovery. - Escape beat
A beat that occurs when the sinus node fails to fire or a conduction block is present. An escape beat originates from other parts of the conduction system. It may be supraventricular or ventricular in origin.
F
G
H
I
J
K
L
M
N
O
P
- P wave
Represents the depolarisation of the atria. The P wave precedes the QRS complex on the EKG. - PQ interval
Represents the atrioventricular conduction and is measured from the beginning of the P wave to the beginning of the QRS complex. Normal duration: 0.12-0.22 seconds.
Q
- QRS complex
Succeeds the P wave and represents the depolarization of the ventricles beginning with the septum and ending with the ventricular walls. Normally the QRS is less than 0.12 seconds in duration. - QT interval
Represents the duration of the ventricular systole. The QT interval varies with the heart rate so a corrected QT interval (QTc) should be calculated. Long QT interval may result in torsades de pointes. Normally the QTc is less than 0.44 seconds in duration. - QT interval – corrected
{QTc} See QT interval above.
R
- R wave
The first positive deflection in the QRS complex. Any succeeding positive deflections in the QRS complex is called R’.
S
- ST segment
Starts from the end of the QRS complex and ends at the beginning of the T wave. The ventricles are fully depolarized. - Supraventricular
Refers to rhythms or beats originating above (supra) the ventricles. For example a supraventricular tachycardia.
T
- T wave
Succeeds the QRS complex and represents ventricular repolarization.
U
- U wave
Succeeds the T wave and represents late ventricular repolarization. The U wave may not be visible.
V
- Ventricular
Refers to rhythms or beats originating in the ventricles. For example a ventricular escape beat.
