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→The QT interval
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QT prolongation is often treated with beta blockers. | 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 | <flash>file=QTc.swf|width=300|height=200|quality=best|align=right|salign=R||bgcolor=#FFF5F5</flash> | ||
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]] | [[Image:Formule_QTc.png]] | ||
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On modern ECG machines, the QTc is given. However, the machines are not always capable of recognizing the correct QT time. Therefore, it is important to check this manually. | On modern ECG machines, the QTc is given. However, the machines are not always capable of recognizing the correct QT time. Therefore, it is important to check this manually. | ||
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. 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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#Calculate QTc according to Bazett: [[Image:Formule_QTc.png]] | #Calculate QTc according to Bazett: [[Image:Formule_QTc.png]] | ||
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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. | ||