Difficult QT: Difference between revisions
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* The QT interval ends where the tangent and the baseline cross. | * The QT interval ends where the tangent and the baseline cross. | ||
* The QT interval is the time in milliseconds between the start and end of the QT interval. | * The QT interval is the time in milliseconds between the start and end of the QT interval. | ||
* If the QRS interval exceeds 120 millisseconds, than some specialists advice to deduct the amount of milliseconds that exceeds 120 | * If the QRS interval exceeds 120 millisseconds, than some specialists advice to deduct the amount of milliseconds that exceeds 120 ms from the QT interval (i.e. if QRS is 140 ms and QT is 480, then 140-120ms=20ms should be deducted from the QT interval, yielding 460ms). | ||
=== | ===QTc is the heart rate corrected QT interval=== | ||
* | * The QT interval should be corrected for the heart rate, as the QT interval shortens with increasing heartrate. | ||
* | * Bazetts formula: [[Image:Formule QTc.png]], can be used to calculate the QTc: the heart rate corrected QT. When entering the formula the RR interval should be entered in seconds. The preceding RR interval should be used. You can also use this [[QTc calculator]] | ||
* Preferably one uses the average of three QTc | |||
* | |||
{{clr}} | {{clr}} | ||
=== | ===Examples=== | ||
[[Image:lastigeQT1.png|thumb| | [[Image:lastigeQT1.png|thumb| The T wave is broad, but the tangent crosses the baseline before the T wave joins the baseline. The QT interval would be overestimated when this last definition of the end of the T wave would be used.]] | ||
[[Image:lastigeQT2.png|thumb| | [[Image:lastigeQT2.png|thumb| The ECG does not meet the baseline after the end of the T wave. Still, the crossing of the tangent and baseline should be used for measurements.]] | ||
[[Image:lastigeQT3.png|thumb| | [[Image:lastigeQT3.png|thumb| A bifasic T wave. The tangent to the 'hump' with the largest amplitude is chosen. This can change from beat to beat, making it more important to average several measurements.]] | ||
==References== | |||
== | |||
<biblio> | <biblio> | ||
#Lepeschkin pmid=14954534 | #Lepeschkin pmid=14954534 | ||