Conduction: Difference between revisions

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'''The normal PQ interval is between 0.12 and 0.20 seconds'''.
'''The normal PQ interval is between 0.12 and 0.20 seconds'''.


A prolonged PQ interval is a sign of a degradation of the conduction system, increased vagal tone (Bezold-Jarisch reflex), or it can be pharmacologically induced.  
A prolonged PQ interval is a sign of a degradation of the conduction system or increased vagal tone (Bezold-Jarisch reflex), or it can be pharmacologically induced.  


This is called [[Arrhythmias#Atrioventricular_block|1st, 2nd or 3rd degree AV block]].
This is called [[Arrhythmias#Atrioventricular_block|1st, 2nd or 3rd degree AV block]].


A short PQ interval can be seen in the [[Arrhythmias#WPW_syndrome|WPW syndrome]] in which a faster connection exists between the atria and the ventricles.
A short PQ interval can be seen in the [[Arrhythmias#WPW_syndrome|WPW syndrome]] in which faster-than-normal conduction exists between the atria and the ventricles.


==The QRS duration==
==The QRS duration==
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==The QT interval==
==The QT interval==
[[File:Tangent QT.png|thumb|400px| The QT interval start at the onset of the Q wave and ends where the tangent line for the steepest part of the T wave intersects with the baseline of the ECG. ]]
[[File:Tangent QT.png|thumb|400px| The QT interval starts at the onset of the Q wave and ends where the tangent line for the steepest part of the T wave intersects with the baseline of the ECG. ]]
'''The normal QTc interval'''
'''The normal QTc interval'''
The QT interval indicates how fast the ventricles are repolarized and how fast they are ready for a new heart cycle.
The QT interval indicates how fast the ventricles are repolarized and how fast they are ready for a new heart cycle.
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If QTc is < 340ms [[Short_QT_Syndrome|short QT syndrome]] can be considered.
If QTc is < 340ms [[Short_QT_Syndrome|short QT syndrome]] can be considered.


The QT interval comprises the QRS-complex, the ST-segment, and the T-wave. One difficultly of QT interpretation is that the QT interval gets shorter if the heart rate increases. This can be solved by correcting the QT time for heart rate using the Bazett formula: [[Image:Formule_QTc.png]]
The QT interval comprises the QRS-complex, the ST-segment, and the T-wave. One difficultly of QT interpretation is that the QT interval gets shorter as the heart rate increases. This problem can be solved by correcting the QT time for heart rate using the Bazett formula: [[Image:Formule_QTc.png]]


Thus at a heart rate of 60 bpm, the RR interval is 1 second and the QTc equals QT/1. The '''[[QTc calculator]]''' can be used to easily calculate QTc from the QT and the heart rate or RR interval.
Thus at a heart rate of 60 bpm, the RR interval is 1 second and the QTc equals QT/1. The '''[[QTc calculator]]''' can be used to easily calculate QTc from the QT and the heart rate or RR interval.
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