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[[Image:Surawicz.jpg|120px|thumb|right|Dr Surawicz, founder of the tangent method, still active in November 2006, at age 89.]]
[[Image:Surawicz.jpg|120px|thumb|right|Dr Surawicz, founder of the tangent method, still active in November 2006, at age 89.]]
Although QT prolongation is potentially lethal, measurement of the QT interval by physicians is not standardized, sine different definitions of the end of the T wave exist.<cite>Viskin</cite> Most QT experts define the end of the T wave as the intersection of the steepest tangent line from the end of the T-wave with the base line of the ECG.<cite>Lepeschkin</cite> This leads to the following stepwise approach:
Although QT prolongation is potentially lethal, measurement of the QT interval by physicians is not standardized, since different definitions of the end of the T wave exist.<cite>Viskin</cite> Most QT experts define the end of the T wave as the intersection of the steepest tangent line from the end of the T-wave with the base line of the ECG.<cite>Lepeschkin</cite> This leads to the following stepwise approach:


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In a (serious) prolonged QT time, it takes longer than the normal amount of time for the myocardial cells to be ready for a new cycle. There is a possibility that some cells are not yet repolarized, but that a new cycle is already initiated. These cells are at risk for uncontrolled depolarization, induction of  [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]].
In a pathological prolonged QT time, it takes longer than the normal amount of time for the myocardial cells to be ready for a new cycle. There is a possibility that some cells are not yet repolarized, but that a new cycle is already initiated. These cells are at risk for uncontrolled depolarization, induction of  [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]].


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The QT interval is prolonged in congenital [[long QT syndrome]], but QT prolongation can also occur as a consequence of (a.o.):
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]  
* Medication (anti-arrhythmics, tricyclic antidepressants, phenothiazedes, for a complete list look on [http://www.torsades.org Torsades.org]  
* electrolyte imbalances
* Electrolyte imbalances
* ischemia.  
* Ischemia.  
QT prolongation is often treated with beta blockers.
QT prolongation is often treated with beta blockers.
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