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Conduction: Difference between revisions
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→The QT interval
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==The QT interval== | ==The QT interval== | ||
[[Image:QRSinterval.jpg|thumb| | [[Image:QRSinterval.jpg|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. Click on the image for a larger image]] | ||
'''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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Although QT prolongation is potentially lethal, measurement of the QT interval by physicians is poor as 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 poor as 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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!Stepwise approach to correct measurement of the QT interval | !Stepwise approach to correct measurement of the QT interval | ||
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In a (serious) prolonged QT time, it 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 [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]]. | In a (serious) prolonged QT time, it 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 [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]]. | ||
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! Causes of QT prolongation | ! Causes of QT prolongation | ||
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