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→‎The QT interval
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The QT interval indicates how fast the ventricles are repolarized and how fast they are ready for a new heart cycle. The normal value for QTc(orrected) is: '''440-450ms for men and 450-470ms for women'''. <cite>Moss</cite>
The QT interval indicates how fast the ventricles are repolarized and how fast they are ready for a new heart cycle. The normal value for QTc(orrected) is: '''440-450ms for men and 450-470ms for women'''. <cite>Moss</cite>


A prolonged QT interval can lead to arrhythmias such as [[Torsades de Pointes]] and subsequent [[Ventricular fibrillation]]. The QT interval is prolonged in congenital [[long QT syndrome]], but QT prolongation can also occur as a consequence of (a.o.) medication, electrolyte imbalances and ischemia. QT prolongation is often treated with beta blockers.
A prolonged QT interval can lead to arrhythmias such as [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]]. The QT interval is prolonged in congenital [[long QT syndrome]], but QT prolongation can also occur as a consequence of (a.o.):
* medication (anti-arrhythmics, tricyclic antidepressants, phenothiazedes, for a complete list look on [http://www.torsades.org Torsades.org]
* electrolyte imbalances
* ischemia.  
QT prolongation is often treated with beta blockers.


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::
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::
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In  a (serious) prolonged QT time, is takes longer for the myocardial cells to be ready for a new cardiac cycle. There is a possibility that some cells are not yet repolarized, but that a new cardiac cycle is already initiated. These cells are at risk for uncontrolled depolarization and induce a [[Arrhythmias#Torsade_de_pointes|torsade de pointes]], a ventricular tachycardia.
In  a (serious) prolonged QT time, is takes longer for the myocardial cells to be ready for a new cardiac cycle. There is a possibility that some cells are not yet repolarized, but that a new cardiac cycle is already initiated. These cells are at risk for uncontrolled depolarization and induce a [[Arrhythmias#Torsade_de_pointes|torsade de pointes]], a ventricular tachycardia.
{{clr}}
===Difficult QT intervals===
In some examples of the QT interval it can be difficult to measure a correct QT time. We have made a separate chapter: [[Difficult_QT| Measurement of difficult QT intervals]].
===Causes of a prolonged QT interval===
*Medication (i.e. anti-arrhythmics, tricyclic antidepressants, phenothiazedes, for a complete list look on [http://www.torsades.org Torsades.org]
*Inherited [[Long QT syndrome|long QT syndrome]] (LQTS)
*Cerebral (subarachnoid haemorrhage, stroke,  trauma)
*Post infarct


===Short QT syndrome===
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.
{{clr}}


== References ==
== References ==
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